Construction Guidelines for Clay Masonry

Acrobat Edition

CLAY MASONRYCONSTRUCTION GUIDELINES FOR

C o n s t r u c t i o n G u i d e l i n e s f o r C l a y M a s o n r y

This publication, its contents and format are copyright of the Clay Brick and Paver Institute. This Acrobat editionmay be stored and reproduced for individual reference and study without alteration or amendment. The ClayBrick and Paver Institute is wholly sponsored by the Australian clay brick, block and paver industry. Local orstate regulations may require variation from the practices and recommendations contained in this publication.While the contents of this publication are believed to be accurate and complete, the information given is intendedfor general guidance and does not replace the services of professional advisers on specific projects. The authorand the Clay Brick and Paver Institute cannot accept any liability whatsoever regarding the contents of thispublication. Copyright © Clay Brick and Paver Institute 2001. ABN 30 003 873 309

Clay Brick and Paver Institute

PO Box 6567, Baulkham Hills BC, NSW 2153, AustraliaTel (02) 9629 4922Fax (02) 9629 [email protected]

Clay masonry has a long and illustrious record of providing durable andattractive buildings that sustain their performance with minimal maintenance.This manual draws together a wealth of industry good practicerecommendations to provide general guidance for the construction of claymasonry in buildings. Reference is made throughout to the Building Code ofAustralia and relevant Australian standards including AS 3700 MasonryStructures and its commentary.Also discussed are material requirements (as they relate to construction),workmanship, tolerances, temporary bracing, cleaning, site control testing, andcompliance assessment.Typical details for masonry construction are set out in Manual 9, Detailing ofClay Masonry Walls, available from the Clay Brick and Paver Institute. Also inthis series are Manual 4, Design of Clay Masonry for Wind & Earthquake andManual 5, Fire Resistance Levels for Clay Brick Walls.Cover: On a 2.65 ha site in Sydney’s East Redfern, Moore Park Gardens offers 560 residentialunits in 14 buildings including a brick-clad 24-storey tower and a series of lower apartmentbuildings. Architect: Allen, Jack + Cottier. Photograph by Jackie Dean, Dean Photographics.

First published April 2001ISBN 0-947160-05-1

Prepared by:Dr Stephen LawrenceSPL Consulting Pty Ltd

http://www.claybrick.com.au

mailto:[email protected]

1 Introduction .................................................................................. 4

2 AS 3700 construction requirements ................................................ 5

3 Materials .......................................................................................63.1 General ............................................................................................... 63.2 Units .................................................................................................. 63.3 Mortar ................................................................................................ 7

3.3.1 General .................................................................................... 73.3.2 Bond between mortar and units ................................................. 83.3.3 Composition ............................................................................. 93.3.4 Sand ......................................................................................103.3.5 Cement .................................................................................. 123.3.6 Lime ......................................................................................123.3.7 Water ..................................................................................... 133.3.8 Admixtures ............................................................................. 133.3.9 Curing ....................................................................................163.3.10 Mixing ....................................................................................16

3.4 Grout ................................................................................................ 17

4 Workmanship ...............................................................................184.1 General ............................................................................................. 184.2 Joints ................................................................................................18

4.2.1 Mortar joints ...........................................................................184.2.2 Control joints .......................................................................... 19

4.3 Flashing and damp-proof courses .........................................................194.4 Wall ties & connectors ..................................................................... 20

4.4.1 General .................................................................................. 204.4.2 Installation ..............................................................................214.4.3 Spacing ..................................................................................224.4.4 Common abuses ..................................................................... 22

4.5 Lintels ...............................................................................................234.6 Grouting ............................................................................................23

5 Tolerances ................................................................................... 245.1 General ............................................................................................. 245.2 Structural tolerances ........................................................................... 245.3 Appearance ....................................................................................... 24

6 Temporary bracing ....................................................................... 25

7 Cleaning of clay masonry .............................................................. 267.1 Introduction ....................................................................................... 267.2 Cleaning mortar smears from masonry ................................................. 26

7.2.1 General .................................................................................. 267.2.2 Cleaning with hydrochloric acid ................................................ 267.2.3 Cleaning external masonry ....................................................... 277.2.4 Cleaning internal masonry ........................................................ 287.2.5 Other acids .............................................................................287.2.6 Proprietary cleaning compounds ............................................... 287.2.7 High pressure water cleaning ....................................................29

7.3 Identifying & cleaning stains on masonry ................................................... 297.3.1 Efflorescence ...........................................................................297.3.2 Vanadium stains ......................................................................307.3.3 Manganese stains ................................................................... 317.3.4 Stains from mortar ingredients .................................................. 31

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Ta b l e o f C o n t e n t s

CBPI Manual 10 : Construction Guidelines for Clay Masonry, published April 2001

8 Testing of masonry ....................................................................... 328.1 General ............................................................................................. 328.2 Quality control testing of special masonry ..............................................328.3 Compressive strength testing ................................................................338.4 Flexural strength testing ...................................................................... 348.5 Assessment of compliance .................................................................. 348.6 When masonry does not comply .......................................................... 35

9 References .................................................................................. 36

Figures1. Staining from ground water ........................................................................... 62. Typical sand grading envelope for mortar .......................................................113. Typical effect on bond strength by using clay as a plasticiser ........................... 154. Typical effect of overdosing air entrainer ........................................................ 155. Effects of bulking on shovels of cement (top) and sand (bottom) ......................166. Varieties of joint finishes ..............................................................................187. Temporary gap filler inserted in a control joint

(remove before sealing the joint) .................................................................. 198. Methods of sealing control joints .................................................................. 199. Control gap sealant squeezed out by joint contraction .....................................1910. Incorrect installation of ties at more than the rated cavity width ....................... 2111. Structural tolerances for out of plumb (within each storey) .............................. 2412. Example of perpend thickness variation .........................................................2413. Damage to mortar joints by high-pressure cleaning ........................................ 2914. Efflorescence from calcium being released from mortar ................................... 3015. Example quality control chart .......................................................................3316. Schematic arrangement of bond wrench test ................................................. 3417. Example compliance assessment chart ......................................................... 35

Tables1. Limiting heights for masonry under construction

(walls with vertical supports at 4 m centres, age 3 to 7 days) .........................25

2. Limiting heights for freestanding masonry walls (sheltered suburban environments, building height up to 4 m) ........................ 25

3CBPI Manual 10 : Construction Guidelines for Clay Masonry, published April 2001

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1 . I n t r o d u c t i o n

This manual provides guidance forthe construction of clay masonry inbuildings. The guidance is of ageneral nature and representsindustry recommendations for goodpractice. It should always berecognised that alternative methodsexist, and that they might bepreferred in some situations forarchitectural, geographical or otherreasons.In conjunction with this manual,appropriate reference should bemade to the Building Code ofAustralia (BCA)1 and the variousrelevant Australian standards,including Masonry Structures (AS 3700)2 with its Commentary3.

Because masonry is assembled onsite, correct construction practices areprobably more critical forperformance than is the case withsome other materials. This manualdiscusses the important requirementsfor materials (as they relate toconstruction), workmanship,tolerances, temporary bracing,cleaning, site control testing, andcompliance assessment.Typical details for masonryconstruction are presented in Manual94 of this series.


2 . AS 3700 c on s t r u c t i o n r e qu i r emen t s

The masonry structures code AS 3700 contains requirements forconstruction, including materials,workmanship, tolerances, sitecontrol, grouting, cleaning andtesting of in situ masonry. Because ofthe performance nature of the code,these are mostly expressed in non-prescriptive terms. For example, themasonry must be constructed insuch a way that the requirements ofthe code for strength, durability, etcare satisfied. The purpose of thismanual is to recommend ways inwhich these requirements of AS 3700 can be fulfilled.Masonry can be nominated asSpecial Masonry as a part of thedesign, and this brings with it certainrequirements for construction andtesting. Masonry nominated in thisway is assumed to have higher thanusual strength, and this must beverified by site control testing.

To date, there has been no attempt inAustralia to base partial safety factorson the level of on-site supervision asis done in some parts of the world,but the code might incorporate this infuture. If it does, designers will beable to benefit from the specificationand execution of a higher level of sitesupervision and control, leading togreater efficiency in the design.The main purpose of the constructionsection in AS 3700 is to ensure thatthe masonry is built in accordancewith the design, as specified in thejob documents. So, for example, it isnecessary to use the bonding patternspecified, to minimise cutting ofunits, to only cut holes and chaseswhere specified, and to properlybuild-in all wall ties and accessories.Specific requirements of AS 3700 arediscussed in the following sections.

5CBPI Manual 10 : Construction Guidelines for Clay Masonry, published April 2001

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3 . Ma t e r i a l s

3.1 GeneralIt is important to ensure that thematerials used in construction meetthe specification in every respect.This requires that all relevantproperties must be checked, ifnecessary by obtaining theappropriate test certificates from themanufacturer or supplier. Thischecking process should encompassthe masonry units, cement, wall tiesand accessories.

The job documents should show thefollowing information:

• Category (for example, solid), type(for example, clay) and work size(for example, 230 x 110 x 76mm) of the masonry units.

• Compressive strength (for example,10 MPa) of the masonry units.

• Proportions or classification of themortar (for example, 1:1:6 or M3).

• Joint finish, depth of raking (if any)and bond pattern.

• Salt attack resistance grade for theunits.

• Wall tie classification and strengthand stiffness of accessories (whenused).

• Any special properties orrequirements, such as site controltesting.

• Other necessary properties such aslateral modulus of rupture of theunits, grout strength, reinforcementgrade, etc.

Correct attention to the specificationboth prior to and during constructionwill ensure that the masonry isproperly constructed to meet thedesign requirements and remainsserviceable and free of faults duringits lifetime.

All materials, especially cement, limeand masonry units, must be properlystored on site and adequatelyprotected against water damage.

3.2 UnitsUnits should be blended from thepacks during laying to eliminatebanding and excessive colourvariation and ensure a satisfactoryappearance in the finished masonry.Especially in the case of two-storeyconstruction, all units should bedelivered at the start of the job andstacked on site to facilitate blendingfrom the packs.

Second-hand units should not beused unless specified. After theyhave been bedded in mortar – evensoft lime mortar – units will have amortar residue clogging the beddingsurface pores, making it difficult forthem to bond properly with mortarupon re-use.

Masonry units of all types must beprotected on site from moisture andcontaminants from the ground, thatcan cause problems withefflorescence and salt attack in thecompleted masonry. Entry of saltsfrom the ground into the units willlead to unsightly efflorescence later,as the salts are mobilised bymoisture from rain and theatmosphere. High moisture contentat the time of laying can causeproblems such as poor bondstrength, efflorescence andshrinkage. It is stronglyrecommended that the masonry unitsshould be stacked clear of theground, for example on pallets, andcovered to give protection from therain (see Figure 1).

Figure 1. Staining from ground water


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Units should not be wetted prior tolaying except as a last resort, in therare circumstance when it is knownto be necessary to ensure satisfactorybond. It is far preferable to adjustcompatibility of mortar and units bythe appropriate use of sands andmortar admixtures (see Section 3.3)than to indiscriminately wet the unitsto lower their suction.

Cutting of units should be minimised.While it is permissible to cut unitswith a bolster, the preferred methodis with a masonry saw. Roughly cutor broken ends should never beallowed to protrude into the wallcavity. For loadbearing masonry thatis classified as Special Masonry, anyhorizontal cutting of units must bedone with a masonry saw.

3.3 Mortar3.3.1 General

The Masonry Code is generallywritten in performance terms. Itrequires that mortar provide adequateworkability, appropriate durability andthe ability to impart to the masonrythe required compressive and tensilestrengths. It is written in this way tofree specifiers and bricklayers fromthe rigidity of past traditional mortarmix proportions and to facilitate thedevelopment and use of new mortartypes that will better match particulartypes of masonry units.

AS 3700 is based on an expectationthat all masonry will have acharacteristic flexural tensile strengthof not less than 0.20 MPa. This is toencourage the proper matching ofmortar to the characteristics of themasonry units in each particularcase. With some care this can beachieved, but if this matching is notcarried out, the appropriate level ofstrength might not be reached, evenwith high standards of workmanship.

Joint mortar determines the overallsoundness of masonry. It bonds theunits together in such a way that theapplied loads can be resisted, whileproviding a construction method thatmakes possible the wide variety ofshapes characteristic of masonry. Itperforms the following functions:

• Accommodates variations in unitsize and shape – a nominal jointthickness of 10 mm is usuallyadequate for this purpose.

• Provides adhesive bond strengthsufficient to resist lateral loads andto provide overall robustness.

• Encourages even bedding of theunits and sufficient strength toresist compressive loads.

• Provides a weather-tight anddurable wall by sealing the jointsbetween units.

• Provides aesthetic effects byvarious joint treatments,pigmentation, bonding patternsand so on.

The most important functionalproperties of mortar are itsconsistency, its durability and itsability to bond with the masonryunits. All of these can be significantlyaffected by workmanship and site practices.

It is important that the mortaringredients and mix compositionshould be exactly as specified.Correct matching of mortar tomasonry units involves many factorsand departures from the specificationduring construction can lead toserious problems. A particular risk isthat the cement used might not bethe same as that specified. Blendedcements are not considered by AS 3700 to be exactly equivalent toPortland cement and can thereforenot be directly substituted in thesame mix proportions (see Section 3.3.3).

There are no clear guidelines forconsistency of mortar. Consistencycan be defined as the ability of themortar to be spread to form a jointwithout undue segregation of theingredients. A flow table is thetraditional laboratory method formeasurement of this property but inrecent years a cone penetrometer hasbecome the preferred method.


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However, testing of fresh mortar inthis way is usually only useful forresearch purposes and experienceshows that the amount of water to beadded for workability is best left tothe bricklayer.

It is difficult to use a mortar that istoo wet or too dry and, apart fromthe possible adverse effects ofadmixtures (see later), the mostsuitable mortar for the bricklayer willusually impart the best properties tothe masonry.

When wet mortar and masonry unitscome into contact, a certain amountof water is sucked into the units.This movement is beneficial to bond,but should not be so great as toleave the mortar with insufficientmoisture for proper setting. Theability of the mortar to retainsufficient water against the suction ofthe unit is called water retentivity andis thus one of the important factorsin promoting tensile bond strength. Itis defined as the ability of the mortarto retain moisture against a standardsuction applied for one minute (tosimulate the suction effect producedby the masonry unit).

Water retentivity is particularlyimportant for mortars used with high-suction semi-dry-pressed bricks.Good water retentivity provides threebenefits:

• Limiting the bleeding of water fromthe mortar.

• Preventing rapid stiffening of themortar bed before units are laid forthe next course.

• Retaining sufficient water in thejoint for hydration of the cement.

Water retentivity can be controlled bythe choice of an appropriate sandgrading (see Section 3.3.4) and tosome extent by the choice of mortarcomposition. Mixes with a higherproportion of lime (such as 1:2:9)will usually exhibit a higher waterretentivity than others (such as1:1/4:3).

Durability of masonry mortar is asimportant as strength and isgoverned by the mortar classificationsystem of AS 3700 (see Section3.3.3). While it is also stronglyinfluenced by joint finishing, it hasbeen found that durability of mortarincreases markedly as the cementcontent increases.

There are no requirements for routinetesting of masonry mortar for sitecontrol purposes. Only in exceptionalcircumstances – if problems areevident and investigation is required– should testing of the mortar becontemplated. Even then, the bestcourse of action is to test theassembled masonry wheneverpossible, rather than the mortaralone. Testing procedures formasonry are described in Section 8.3.3.2 Bond between mortar

and units

Bond strength between mortar andmasonry units is a more importantproperty than compressive strengthbecause it determines the strength ofa wall against wind and earthquake,as well as its general serviceability. Inmasonry buildings, failure is morelikely to occur from lateral loads,particularly wind, than from verticalloads. Tensile bond strength isstrongly affected by mortar type. It isusually enhanced by the presence oflime and may be markedly reducedby workability admixtures. It is notalways the case that tensile bondstrength increases with cementcontent.

The formation of bond involvescomplex mechanisms but thefollowing are known to be majorfactors:

• Sand grading – an excess of clayparticles passing the 75-micronsieve will reduce bond strength. Itis common for bricklayers to use a‘brickies sand’ with high claycontent that improves workability.This type of sand may besatisfactory with some clay unitsbut is certainly not for all. If theclay content is too high the bondstrength will be reduced as aconsequence.



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• AS 3700 permits the use ofplasticisers and workability agents.However, the use of admixturessuch as air entraining chemicals –many of which are virtuallyindistinguishable from soaps ordetergents – always has the effectof reducing the bond strength.When accurately batched, theimprovement in workability canoffset the reduction in strength, butover-dosing or over-mixingproduces large reductions instrength.

3.3.3 Composition

Mortar has traditionally beenspecified in a prescriptive way bygiving the proportions of cement,lime and sand. More recently,durability and strength of mortar arecontrolled by a classification systemgiven in AS 3700, comprising gradesM1, M2, M3 and M4. Typical mixproportions to achieve these gradesare given in the code. The masonrydesigner should choose anappropriate grade for the mortar andspecify either this grade or theproportions on the documents.

The conventional notation for mortarsis cement, lime and sand in thatorder, with proportions (by volume)indicated by C, L and S respectively,each followed by a number. Themain cementing agent is alwaysgiven as unity and the traditionalproportion of cementitious agent tosand is one to three. Common mixesare C1:L1/2:S41/2 and C1:L1:S6. Theletters are often omitted and only thenumbers are shown, for example1:1:6. Only cement and sand areshown if there is no lime. With theincreased prevalence of blendedcements in recent years it is vital tospecify the type of cement unless itis Portland. A mix where the type ofcement is not specified shouldalways be assumed to requirePortland (type GP) cement.

AS 3700 gives the mortar gradesrequired in order to ensuresatisfactory durability in variousexposure environments. By far thecommonest mortar grades are M2

and M3. Most masonry in housingand small-scale structures wherethe environment is interior or mildexposure uses an M2 mortar, whilefor general work and loadbearingwalls an M3 mortar is moresuitable. Occasionally an M4mortar is used for applicationswhere high compressive strength orhigh durability is required. M1mortar can only be used in heritageor restoration work.

In the AS 3700 table of deemed-to-satisfy proportions (Table 10.1) themixes classified as M3 include thefollowing:

• 1:1:6 with Portland cement

• 1:5 with Portland cement (andwater thickener)

• 1:1:5 with blended cement

• 1:4 with blended cement (andwater thickener)

• 1:4 with masonry cement

The table also shows for whichtype of units each mortar issuitable. The table clearlyemphasises the importance ofcement type, for example an M3mortar requires the followingproportions with the differentcement types:

• 1:1:6 with Portland cement

• 1:1:5 with blended cement

• 1:4 with masonry cement

The requirements of AS 3700 areall expressed by reference to themortar classification rather than the precise mix composition. It istherefore preferable, at least formajor jobs, for the documents tospecify the mortar classification and leave the actual mixproportions to be determined onsite, based on the available cementand sand types.


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One of the most commonmisconceptions about masonry isthat increasing the cement content inthe mortar will increase the tensilebond strength. While an increase incement content will generally causean increase in durability andcompressive strength of mortar (andtherefore the masonry made with it)the same is not necessarily true fortensile bond strength.

The formation of bond betweenmasonry units and mortar relies oncomplex mechanisms that are not yetfully understood.

These are partly dependent oncement hydration, but they alsodepend on the transport of moistureand fine particles in the interfacialzone and on the degree of matchingbetween the properties of the fluidmortar and the suction and surfacecharacteristics of the unit. In thiscontext, simply increasing the cementcontent in the mix will not guaranteean increase in tensile strength.

In addition to the main ingredients, arange of mortar admixtures isavailable including those forworkability, bond enhancement,colouring and retardation of setting.Thin-bed mortars are speciallyformulated and should be used onlyin accordance with themanufacturer’s instructions.

The following general points shouldbe noted and are discussed in detaillater:

• Sand should be free of salts andorganic matter. The particle sizegrading and clay content are themost important properties thatrequire controlling.

• Cement type is important becausenot all cements are equal. Portlandcement, blended cement andmasonry cement should be used indifferent proportions, as requiredby AS 3700.

• Lime is beneficial to masonrymortar. It adds workability,increases water retentivity andenhances bond strength anddurability.

• Water should be clean and free ofimpurities.

• Admixtures should be used withcare as over-dosing can causesevere problems.

The following sections discuss theconstituents in turn, along withvarious other aspects of masonrymortars.3.3.4 Sand

As well as the need for sand to beclean and free of salts and organicmatter it must have a suitablegrading and should not contain toomuch clay. The grading of sand hasan influence on the properties ofmortar in both the plastic andhardened conditions, howeverquantifying this influence is difficult.Sand grading is given in terms ofpercentage passing a standard set ofsieves and specifications sometimesinclude a grading envelope. However,this approach of specifying a gradingenvelope is not recommended formasonry mortars, becausesatisfactory performance can also beachieved with sands whose gradingcurves fall outside the acceptedenvelopes.



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Figure 2 shows a set of grading limitsthat was previously recommended inthe commentary to AS 3700. Thecurves are similar to grading limitsthat have been recommended inother parts of the world.

However, they should be taken as aguide only and should not be used ina specification for building works.Experience is the best guide to thesuitability of any particular sand.

A generally accepted limit for goodmasonry mortar to be used with clayunits is that the sand should notcontain more than 10 per centpassing the 75-micron sieve and notmore than 1 per cent retained on the2.36 mm sieve. However, sandsoutside these limits can give quiteadequate strength and durabilityperformance. The most importantrequirement is that the sand shouldproduce a mortar compatible withthe units and the best guide for thisis experience. In difficult situations, itcan be useful to carry out a trial mixand test the required properties withthe units to be used on the job.

Material below 75 microns in size isusually clay and can produce thefollowing problems:

• Smears and stains on the finishedsurface of the masonry caused bythe clay particles. These smearscan be difficult to remove.

• Reduction in mortar strength andparticularly tensile bond strength ofthe masonry.

• A ‘sticky’ mortar mix thatencourages the mason to overdosewith air entraining admixtures.

• Durability problems caused by thebreaking down of clay particlesunder cycles of wetting and drying.

• The mortar will have goodworkability without the addition oflime, tempting the mason to omitlime from the mix and therebyinvite adverse effects.

On the other hand, small amounts of clay can be quite useful as aplasticiser and can produce aworkable mix without the need forproprietary plasticisers that are sosusceptible to overdosing. Whenproblems arise they are not becauseof the presence of clay but thepresence of too much. In manycases, the best course of action is toblend sand from equal parts of ‘fatty’sand and washed sand to give a mixthat provides a suitable workabilityand adequate strength. Good sandsuppliers will do this at the source of supply.

When sand for use with clay unitscontains very fine material that issilica rather than clay, experiencesuggests that the use of a cellulose-type water thickener can improvetensile bond strength.

Figure 2. Typical sand grading envelope for mortar


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3.3.6 Lime

Lime is an important ingredient inmasonry mortar and confers manybenefits, including plasticity duringsetting, self-healing of minor cracksthroughout the life of the masonry andpromotion of good bond with clayunits. For at least 2000 years,extending into the twentieth century,lime was the primary cementitiousmaterial in mortar and our citiescontain many functional buildingsconstructed with L1:S3 mortars. Now that Portland cement is the mainagent, the benefits of lime can easilybe overlooked. The self-healingproperty of lime repairs micro-cracksthat can form because of atmosphericconditions, long-term expansion orshrinkage. Lime also reduces thespeed of hardening, allowing masonryto take up minor movementsincidental to construction.

Some work done in recent years onthe conditions at the brick/mortarinterface has improved ourunderstanding of the mechanism ofbonding and in particular hasprovided evidence in support of thebenefits of using lime. As well asimparting plasticity to the mix duringsetting, the presence of lime canproduce an initial coating on thesurface of clay bricks, that appears to promote bonding as the cement hydrates.

Lime can be used as dry hydratedlime, added to the mortar duringmixing, or as lime putty. The latter hasthe advantage of imparting to the mixa higher plasticity, with attendantadvantages for workability, tensilebond strength and water permeability.However, the use of lime puttyrequires care to ensure that mixes areconsistent and that the desired mixproportions are achieved. Lime puttycan be prepared by mixing dryhydrated lime with water to a creamyconsistency and letting it stand for 16 hours or more to ‘fatten up’ before use.


3.3.5 Cement

Three types of cement are commonlyused for masonry in Australia.

General-purpose (Type GP) cement isprobably the most common and ispreferred for high quality work andstructures carrying high levels of load.It consists primarily of Portlandcement.

Blended cements (Type GB),sometimes known as ‘Builders’cements, are becoming increasinglycommon, especially for smaller-scalework. They consist primarily ofPortland cement mixed with fly ash or blast furnace slag. Portland andblended cements must comply withAS 39725.

The third type is masonry cement,which is available in some parts ofAustralia and contains additions ofinert materials in various proportions.Masonry cements are usually blendsof Portland cement with variousingredients such as fly ash, blastfurnace slag, finely ground limestone,building lime, plasticisers and airentrainer. Their constituents andquality can vary widely betweendifferent regions. The onus is on themanufacturer of such cements todemonstrate that their use will resultin masonry meeting the requirementsof AS 3700 and, in particular, that itwill not result in strengths belowthose required.

It is important to realise that blendedcements and masonry cementscannot replace Type GP cement inthe same proportions. They generallygive slower strength development andlower final strength. The deemed-to-satisfy mix compositions given in AS3700 allow for this fact, as discussedin Section 3.3.3. It follows that thetype of cement required for a jobshould be specified along with themix proportions; otherwise it shouldbe assumed that Type GP cement isintended.


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Because of the potential benefits, theuse of lime is widely encouraged forclay masonry. Admixtures shouldnever be used to replace lime withouttest data to show that strength andother properties will not be adversely affected.

3.3.7 Water

Water is the lubricant that allows theother constituents to be brought to aworkable consistency. It must be freefrom harmful quantities of anythingdeleterious to the masonry, thereinforcement or any embeddeditems. In particular it should be freeof suspended fine particles anddissolved salts or other compounds.The usual test for satisfactory wateris that it be potable (drinkable).

Water also brings about hydration ofthe cement, that is ultimatelyresponsible for the tensile andcompressive strengths and thedurability of the masonry. Withmasonry there is not the samerelationship between water/cementratio and strength as there is withconcrete. This is because, in the caseof masonry, large amounts of waterare removed from the wet mortar bythe suction of the units. It is thenpossible that there will not besufficient water remaining to ensurefull hydration of the cement. Inaddition, masonry is not given thebenefits of good curing that are oftenavailable with concrete.

Experience has shown that it is bestnot to control the amount of wateradded to a mortar – it should usuallybe mixed as wet as possible to allowit to flow into the surfaceirregularities of the units. Thebricklayer will generally add sufficientwater for good workability and thiswill result in the best strength underthe circumstances.

3.3.8 Admixtures

Inappropriate use of admixtures inmasonry mortar is a very commonsource of problems. AS 3700restricts mortar admixtures to certaintypes and these must satisfy therelevant standards. The following arepermitted:

• Plasticisers and air entrainingagents – designed to improvemortar workability.

• Methylcellulose water thickeners –designed to enhance waterretentivity for use with concreteand calcium silicate units.

• Colouring pigments.

• Set-retarding agents – usuallyadded at the batching plant anddesigned to provide up to threedays setting time.

• Bonding polymers – designed toenhance bond strength (these arelittle used in Australia).

The admixtures should only be of atype specifically designed for usewith masonry mortars. Anyadmixture not of the types listedabove must have its performanceverified by testing with the masonryunits to be used on the job, andthese tests must show that thestrength and durability properties arenot adversely affected by the use ofthe admixture.

Chemical admixtures such asplasticisers and workability agentsshould never be used as substitutesfor lime. Most proprietary airentraining agents are chemicallysimilar to detergents and they alwaysreduce the strength of the mortar.This reduction might not be seriousbut it should be recognised that theuse of these agents is prone tooverdosing and excessive mixingtime, both of which have a markedeffect in reducing strength, especiallytensile bond.


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It should be borne in mind that thepigment adds to the total finescontent of the mix and will thereforeaffect the workability and waterretention properties (and hence thebond strength). Liquid suspensionsare the most convenient but careshould be taken if the liquid mediumis an air-entraining agent. Apparentfading of pigmented mortars can becaused by too little cement in themix, over-use of air entrainingagents, degradation due to aggressiveatmosphere or moisture, and lightcoloured staining due to efflorescenceor chemical deposits.

Set-retarding admixtures should only be used in pre-mixed mortarsbatched in a factory and must beused within their retardation period or discarded. They are usually onlypractical for large construction jobsand can offer the advantage ofimproved quality control. However, it is essential that the adequateperformance of masonry built withthese mortars is demonstrated and itis advisable to carry out routine sitetesting to confirm adequate strength.Experience has shown the possibilityof drastic reductions in tensile bond strength and durability whenretarded mortars are used with high suction units.

In addition to the admixtures referred to above there are variousproprietary permeability-reducing(‘waterproofing’) additives. It isrecommended they should not berelied upon as a substitute formembrane damp-proof coursesunless there is strong local evidencethat foundation movements are verysmall and that the admixtures have aproven history of reliableperformance. Any crack in a mortarcourse containing one of theseadmixtures will destroy the water-resisting effect and the use ofexcessive quantities of admixture willseriously weaken the mortar. Wherethese admixtures are employed (forexample in copings) this should onlybe in conjunction with C1:S3 mortar.

It is well established that theoptimum tensile bond strength withconcrete and calcium silicate units isachieved by using a cellulose-typewater thickener and appropriate sand.The effect of this admixture is toprovide workability to the mix whilereducing the rate at which water canbe removed by the relatively highlong-term suction of the units. Thereis also some evidence that this type of additive can be beneficial withhigh-suction clay units and certaintypes of sand.

When a water thickener is used, itshould be one that is specificallydesigned for masonry mortars andmust only be used at the dosage andin a manner recommended by themanufacturer. Some bricklayers findthese mixes a little too sticky andadding a small quantity of lime (up toone-quarter of the volume of cement)in addition to the water thickener canalleviate this.

The most common admixtures forcolouring mortar are synthetic metaloxides. These mix with the cement toform a pigmented slurry that coats the sand grains. It is generallyrecommended that no more than 10 per cent of pigment (by weight ofcement) should be added, becausethere will be no further increase incolouring. Carbon black should not beadded in proportions greater than 3per cent by weight of cement.


15

Finely powdered clay is sometimesmarketed as an admixture formasonry mortars, to enhanceworkability. While bricklayers find itproduces a readily workable mix, thistype of admixture can have severeeffects on bond strength. As the doseof clay increases, the bond strengthreduces markedly, as illustrated inFigure 3. Lime as a plasticiser doesnot suffer from these adverse effectsand, as explained above, also bringspositive benefits.

Probably the most commonconstruction error in masonry is over-dosing of air entrainer, leading toextremely low bond strength. Whenair is entrained in masonry mortarthe air bubbles behave like ballbearings and increase the workability.However, the entrained air reducesthe contact area between themasonry unit and the mortar andlowers the efficiency of the cementpaste in the mortar. The results canbe a drastic reduction in bondstrength, particularly if the airentrainer is used at more than therecommended dose.

AS 3700 does not have prescribedlimits on entrained air, such as existin some countries, and it is thereforeimperative that builders exercisecaution in the use of theseadmixtures.

Figure 4 illustrates the typical effecton bond strength of increasing thedosage of air entrainer. Much toooften on site the dose used is up to40 times the recommended dose,leading to a drastic reduction in strength.

Figure 3. Typical effect on bond strength by using clay as a plasticiser

Figure 4. Typical effect of overdosing air entrainer


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3.3.9 Curing

It is well established that the strengthof hardened mortar in masonry jointsis considerably greater than would beobtained by testing mouldedspecimens such as cubes. Thisresults from the removal of waterfrom the mortar by the suction of thebricks, lowering the water/cementratio from its initial very high value.However, if all the water that passesinto the units evaporates, the cementin the mortar will not achieve fullhydration. Curing of the masonry willpermit some of the moisture to returnto the joints over time and enhancecement hydration, leading to highercompressive and tensile strengths.

Unlike the case with reinforcedconcrete construction, curing ofmasonry is not common on site. Atthe very least, masonry should beprotected from drying out too rapidlyin hot conditions. The strength valuesused in design are based on an ageof seven days, assuming normalrates of strength development, and ifdrying out interrupts thisdevelopment the required strengthmight not be achieved.

For masonry constructed in a wall,the mass of construction, combinedwith the effect of the cavity (ifpresent), is sufficient to ensure adegree of curing except in very dryconditions. By contrast, site controland laboratory specimens are moreexposed to drying effects. This,together with the fact that they areintended to indicate the full potentialstrength of the masonry, explains therequirement in AS 3700 for thesespecimens to be wrapped in vapour-proof sheet for curing.

3.3.10 Mixing

Specification of an appropriate mortarcomposition is only half the story;achieving it on site is the other half.It is essential that batching methodsshould be such as to ensure that thespecified composition is achieved.While shovel batching is the mostconvenient (and common) it isusually the least accurate and isoften the cause of durabilityproblems resulting from the cementcontent being lower than intended.Mortars with too low a cementcontent can be soft and susceptibleto damage by abrasion and saltcrystallisation.

The lack of accuracy with shovelbatching arises mainly from thedifferent bulking properties of sand,cement and lime. Figure 5 illustratesthe large difference that can occur inthe volume of a shovel of cementand a shovel of sand. Due to thenatural bulking of moist sand thevolume will be much greater, leadingto a mortar with much less than theintended cement content. Volumebatching with buckets or gauge boxeswill avoid this problem.

Figure 5. Effects of bulking onshovels of cement (top)

and sand (bottom)



17

The best method of batching is toadd bagged cement and lime in thecorrect quantities to a mixer ofknown volume and then to fill themixer with sand. The volumecalculations are straightforward andonce they are carried out for aparticular mixer they will not change.

For example, most mixes have avolume of cementitious material(cement and lime) equal to one thirdthe volume of sand. Since thecementitious material fills theinterstices between the sand grains itdoes not add to the overall volume.The volume of cement and limecombined should therefore be one-third of the volume of the mixer. Inthe case of a 1:1:6 mix thiscementitious component would bemade up of half cement and halflime. Once this is added, the mixercan be completely filled with sand(and the required amount of waterfor good workability) and theresulting mix will have the correct proportions.

Mixing time for masonry mortarshould be controlled. A minimum ofsix minutes is recommended becauseshorter times can produce strengthand colour variations in the mortar.While there is no recommendedmaximum time, it is particularlyimportant that mortars with air-entraining admixtures should not beover-mixed. Extended mixing of thesemortars will entrain too much air andlead to very low bond strength.

Mortar must not be used once settinghas commenced but it can be re-tempered to replace water lost byevaporation up to this time. This re-tempering should not extend beyondthe time of initial set of the mortar,which is usually from one to twohours after mixing, depending on the conditions.

3.4 GroutIn reinforced clay masonry, whetherconstructed with steel bars in pocketsor in cores through the blocks, groutmust be incorporated to protect thesteel reinforcement from corrosion. Toachieve this, grout must completelysurround the bars and must containsufficient cement to provide aprotective alkaline environment.

To ensure that the bars are fullysurrounded, the grout must be mixedto a pouring consistency such that allpockets, cores and cavities within themasonry units are filled. Traditionalconcrete technology would suggestthat a high water-cement ratio wouldgive a lower strength for the grout.However three factors should beborne in mind:

• Complete filling of the cores is moreimportant than having a higherstrength grout.

• The units absorb much of the waterout of the grout, reducing the water-cement ratio and at the same timeimproving the bond between thegrout and the unit.

• An increase in the strength of thegrout beyond the strength of theblocks gives a relatively smallerincrease in the strength of themasonry. Because of this, even if ahigh strength grout is used, thestandard places an upper limit onthe value that can be assumed fordesign.

AS 3700 requires that the grout havea cylinder compressive strength of atleast 12 MPa. The ideal mix designfor grout depends on the strengthrequirement and on the size of thecores to be filled. It is usual to use amixture of 50 per cent to 75 per centof sand, with 50 per cent to 25 percent of 5 mm aggregate (roundedriver gravel or pea gravel). Additivessuch as fly ash, silica fume andchemical admixtures can be used,provided they comply with therelevant standards. However, the mostimportant requirement concerning thegrout is for corrosion protection to thereinforcement, and AS 3700 requiresthe cement content to be at least 300kg/m3 to ensure adequate durability.


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4 Wo r kman sh i p

4.1 GeneralIt is important that the type ofbedding (full or face-shell) specifiedin the documents should be followedin the construction. This is becausethe strength of masonry depends onthe type of bedding. Joint thicknessinfluences strength as well asappearance and must therefore beconstructed as specified. Tolerances(see Section 5) are prescribed for anyvariations in joint thickness. Thevertical joints (perpends) must befilled with mortar unless thedocuments indicate otherwise; fillingof these joints has an effect onhorizontal bending strength, waterpenetration resistance, and otherproperties such as soundtransmission. The base course shouldalways be laid on a freshly prepared,horizontal bed of mortar, applied to aclean surface.Various general construction detailsalso require attention. The bonding ofthe masonry units, in particular theunit overlap and the use of headerunits, must be as specified by thedesigner. Toothing must not be usedwhere one wall intersects anotherand they are built at different times.Rather, the wall built first should beracked back or metal ties should beembedded during construction of thefirst wall and incorporated into the

second wall when it is built. Ingeneral, the use of cut units and thecutting of holes and chases shouldbe minimised as far as possible.Chases can have serious adverseeffects on strength, fire resistanceand sound transmission and shouldonly be used within the limitspermitted by the design.The rate of construction of masonryshould match the conditions.Construction that is too rapid canlead to slumping of the work, andexcessively hot and dry or freezingconditions should be avoided. Onceconstructed, the masonry should beallowed to set without disturbance.Initial bond between a masonry unitand mortar is formed quite rapidly,due to suction of water from themortar into the unit, and it is mostimportant that the unit should not bemoved after being tapped intoposition.During wet weather the tops of wallsshould be covered to preventrainwater entering the units, thatcould lead to damage, excessiveshrinkage and efflorescence.Weepholes and cavities betweenmasonry leaves should be kept freeof mortar and other materials.Cavities can be kept clean by using acavity batten that is pulled up as thework proceeds. It is also goodpractice to hose out cavities at theend of each days work. Weepholescan be formed by inserting a duct orother insert, or by using a rod that isremoved once the mortar hasstiffened sufficiently.

4.2 Joints4.2.1 Mortar jointsMortar joints (both bed and perpend)are usually specified as 10 mm inthickness. Any raking, if specified,should not exceed 10 mm depth andshould not penetrate closer than 5mm to any core or perforation incored units or to within 20 mm ofthe cores in hollow units. Tooling ofjoints is particularly beneficial inimproving durability and must alwaysbe carried out as specified. Varioustypes of joint finishes are illustratedin Figure 6.Figure 6. Varieties of joint finishes

ShallowIroned

DeepIroned

StruckFlush

WeatherStruck Raked


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4.2.2 Control jointsControl joints are used in claymasonry to accommodatemovements within the masonry orbetween the masonry and other partsof the building. Such movements canarise from various sources includingfoundation movements, expansion ofthe clay masonry units, thermalmovements and shrinkage ofconcrete elements. When foundationmovement is the cause, the joints arereferred to as articulation joints.Control joints must be kept clear ofmortar droppings and other materialsand properly back-filled with sealantas specified. Figure 7 shows the useof a temporary gap-filling material ina control joint to ensure that it is keptfree of mortar. It is essential that thistemporary filler is removed and thejoint properly filled when constructionof the wall is complete.To ensure proper functioning, it isparticularly important that expansionjoints in clay masonry should befilled only with specifiedcompressible material.

Figure 8 shows two methods of fillingcontrol joints. Flexible sealant shouldbe left well back from the surface toavoid unsightly squeezing out as thejoint contracts (see Figure 9).Control joints should haveappropriate flexible ties (not cavityties) installed across the joint.

4.3 Flashing and damp-proof courses

Correct installation of damp-proofcourses and flashings is one of themost important constructionconsiderations for masonry. AS 3700requires damp-proof courses andflashings to be provided for thefollowing purposes:

• To prevent moisture from movingupward or downward through themasonry.

• To prevent moisture passing fromthe exterior to the interior of abuilding, including passing acrossa cavity.

• To shed moisture from a cavity tothe outer face of a masonry wall.

While chemical parging of damp-proof courses has proven successfulin some areas (for example, WesternAustralia) the use of membranedamp-proof course materials is by farthe most common. Recommendedlocations for flashings and damp-proof courses are given in CBPIManual 9.

Traditionally, membrane damp-proofcourses (DPC) and flashings havebeen embedded in joints with mortarabove and below, not directly laid onthe units.

Figure 8. Methods of sealingcontrol joints

Figure 9. Control gap sealant squeezed out by joint contraction

Figure 7. Temporary gap fillerinserted in a control joint (removebefore sealing the joint)

Impregnatedfoam seal

Closed cell Polyethylenerod backing

Caulking compound


20

4 Wo r kmansh i p

However, there is evidence to suggestthat slip joints, that are oftenimplemented with two layers of DPCmaterial, are more effective if theyare laid directly on the units. Thespecification should be carefullyfollowed in this regard. AS 3700requires the bed joint on which theDPC is laid to be flushed up withmortar, but this does not mean thatcore holes should be filled or that theDPC should necessarily besandwiched within the mortar joint.Joints at the ends of DPC andflashing material should be lapped toa length at least as great as thethickness of the masonry leaf, toguard against moisture migratingalong the lap and penetrating thewall. Care should be taken in storageand handling to avoid puncturingDPC and flashing materials, therebyallowing moisture to pass through.The materials for damp-proofcourses, copings, flashings andweatherings must comply withAS/NZS 29046 and must becorrosion resistant and compatiblewith all materials they will contact inservice. The following are commonmaterials used for this purpose:

• Aluminium

• Copper and copper alloys

• Lead

• Zinc

• Zinc-coated steel

• Bituminous-coated metal

• Bituminous materials withoutmetal centres

• Polyethylene sheet

A membrane DPC should be visibleat the front surface of the wall afterconstruction. This is best achieved byallowing the material to project whilethe masonry is under construction,followed by cutting it off flush orturning the edge down whenconstruction is complete. The mostcommon cause of dampness inmasonry buildings is bridging of theDPC, either because of insufficientprojection from the surface of thejoint or by the application of a rendercoating after construction of the wall.

Any external landscaping orrendering of the wall must not beallowed to bridge the DPC and forma path for moisture to pass above theDPC level.

4.4 Wall ties & connectors4.4.1 GeneralWall ties that interconnect the leavesof a cavity wall or connect a masonrywall to a backup frame of timber orsteel stud are essential structuralcomponents of the building. If theirintegrity fails, there is a significantrisk of the masonry skin falling offthe building in high wind orearthquake. This was one of themost significant causes of failure inthe Newcastle earthquake of 1989.The wall tie standard AS/NZS2699–Part 17 specifies the requiredcharacteristics of ties and AS 3700specifies how they should bedesigned and installed. It is essentialthat these standards should becomplied with.An important feature of AS/NZS2699 is the labelling requirements.These require each package of ties toshow the strength rating (light,medium or heavy duty), the ratedcavity width, the durability category(R0 to R5) and the fasteningrequirements (for veneer ties). Theindividual ties must be colour codedor stamped to indicate the durabilityrating. If colour coding is used itshould be as follows, in order ofincreasing durability (there is nocolour coding for R5, which must bedesigned specifically for eachsituation):

• Green R0 or R1

• Yellow R2

• Red R3

• Blue R4

The builder must ensure that the tiesinstalled into the building complywith the specification in all theserespects. It is particularly importantthat ties should not be used at cavitywidths greater than the rated widthshown on the packaging, becausethe strength rating no longer appliesat any greater width.


21

Figure 10 shows an example ofincorrect installation of a tie atgreater than the rated cavity width(50 mm).

Figure 10. Incorrect installation ofties at more than the rated cavitywidthConnectors used in masonry, forexample across control joints and totie the tops of walls must complywith the appropriate standardAS/NZS 2699–Part 28. Theseconnectors must also have adurability rating (R0 to R5) and mustbe selected and installed inaccordance with the specification.The same colour-coding schemeused for wall ties (see above) orother form of stamping or labellingmust be used to indicate thedurability rating of connectors.Manufacturers test these productsand provide strength values, that areused for the design of criticalconnections such as the tops ofwalls. It is therefore essential that theappropriate types, at the specifiedspacings, should be used in theconstruction.

4.4.2 InstallationAll ties and connectors must be builtinto the masonry as the workproceeds, to ensure that they areproperly embedded in fresh mortar.AS/NZS 2699–Part 1 requires the tiemanufacturer to supply the fastenerfor use with veneer ties. This is animportant requirement, necessary toguard against the risk of electrolyticcorrosion caused by dissimilar metalsbeing in contact. Any such corrosion,leading to disintegration of thefastening, would quickly render theties useless. For this reason veneerties must always be installed usingthe fastener supplied with them.

While veneer ties have traditionallybeen attached to timber framing withnails, there is an increasing tendencyin Australia to require screw fixingsfor strength purposes and this isalready the common practice in NewZealand.All ties must be installed to preventwater transfer across the cavity fromthe outer masonry leaf to the insideof the building. Ties are tested toensure that they will not permit watertransfer if installed level, but anadditional safeguard is provided bygiving them a slight slope towardsthe outside of the wall. However, thisslope should not be too great, or thestrength of the tie connection will beaffected. AS 3700 limits the outwardslope of the ties to not greater than10 mm. Careful planning and settingout should be used to avoid anygreater coursing differences betweenthe leaves of a cavity wall.The strength of embedment of theties in the masonry affects theirability to transfer forces. Themasonry code AS 3700 requires allties to be embedded at least 50 mminto the mortar joint and to have atleast 15 mm remaining cover to theouter surface of the mortar joint. Inthe case of hollow masonry units,laid in face shell bedding, the coresshould be filled with grout or mortar(at least where the ties are located)to provide sufficient embedment forthe ties.Particular care must be taken if theties are bent up or down duringconstruction of a masonry leaf, toensure that they are properlyembedded when the second leaf isconstructed and that they have thecorrect water-shedding slope. Two-part ties can be useful to avoid thetendency to bend ties duringconstruction.

As the wall construction proceeds, it is important to keep mortardroppings out of the cavity (or cleanthem out at the end of each day)because an accumulation ofdroppings adhered to the ties is likely to cause problems of waterpenetration during the life of the building.


22

4 Wo r kmansh i p

Bolts and anchors for attachments(for example roof trusses) can beadded later, in accordance with thespecification.

4.4.3 SpacingTies must be installed at the correctspacings, as specified on thedocuments for the job. It is importantto remember that these spacings canvary from one job to the next andeven for different areas within thesame building. The spacing shouldnever exceed 600 mm in the verticalor horizontal direction. There willgenerally be an overall spacing of tiesfor the wall, for example 450 mm by450 mm, and a requirement foradditional ties to be installed in some locations.Alongside openings, control jointsand edges of a wall, the first row ofties should be within 300 mm of theedge of the masonry. This is toensure that all parts of the masonryare adequately supported. Thisrequirement also applies oppositeintersecting walls and at other pointsof support for the wall.Where a two-storey masonry veneeris continuous past a floor level, thereshould be a row of ties within 300mm below the floor and a separaterow within 300 mm above the levelof the floor. This is to ensure that themasonry in both the upper and lowerstoreys is adequately supported,considering that the floor membraneacts as a very stiff supporting point.These rows are also each required tocontain additional ties (see below).AS 3700 requires fewer additionalties than it has in the past. Doublethe usual number must be installedin rows in the following locations:

• At the top of a single storey veneer.

• Opposite vertical lateral supports(for example intersecting walls) inboth veneer and cavity walls.

• For a continuous multistoreyveneer, in the row immediatelyabove and the row immediatelybelow the intermediate floor level.

As an alternative to using double thenumber of ties, ties of a higherstrength rating could be used but thiswill not usually be practicable.Additional ties are no longer requiredaround edges of door and windowopenings or at control joints. Ingeneral, the requirements should bespecified on the drawings.

4.4.4 Common abusesThere are some common abuses inthe use of wall ties that came to lightin the Newcastle earthquake andhave also been observed at othertimes. These all detract from theperformance of the masonry in termsof either its integrity or its durability.The more common ones are:• Not engaging the ties (bending

down). This can be avoided byusing two-part ties or polymer ties.

• Not embedding the ties for asufficient distance (often due to aninappropriate cavity width).

• Not embedding the ties properly inmortar, resulting in low pulloutstrength.

• Use of sub-standard ties (in termsof strength or corrosion resistance).

• Misalignments of ties across thecavity, resulting in water transferinto the building and reducedstrength.

• Mortar dags in the cavity, leadingto water penetration.

• The cavity cluttered with cables,debris and so on, leading to waterpenetration.

The proper performance of amasonry structure depends on theties being properly designed,specified and installed. AS 3700provides the rules for achieving thisbut lack of compliance is a recurringproblem.


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4.5 LintelsLintels are used to support masonryover openings such as doors andwindows. A lintel should havesufficient strength and stiffness andbe made of a material that iscompatible with the masonry itsupports. Lintels are commonly madefrom the following materials:

• Galvanised or stainless steel

• Reinforced or prestressed concrete(precast or in situ)

• Reinforced or prestressed masonry

• Stone

All lintels must comply with thedurability requirements in AS/NZS2699–Part 39. This standardprovides for durability ratings usingthe same classification system (R0 to R5) as that used for ties andconnectors. The standard requireslintels to have identifying markingsand, in particular, to be colour coded to indicate the durabilityclassification, using the samescheme as for wall ties andconnectors (see Section 4.4.1). This colour coding and theidentifying marks should be visiblewhen the lintel is embedded in the wall.

Lintels, especially those of steel withgalvanised or duplex coatings, mustbe handled carefully to preventdamage before they are installed.Any damage to the coating arisingfrom dropping the lintel or otherimpact, will compromise thecorrosion protection and shorten the life of the lintel.

Correct installation is also vital iflintels are to perform satisfactorily.The specified bearing distances ateach end of the lintel must becomplied with and any specifiedpropping procedure must befollowed. To ensure proper compositeaction with the supported masonry,some lintels should be proppedduring construction.

Where they are used, the propsshould not be removed until themasonry has hardened sufficiently,usually seven days after the masonryis built above the lintel. Steel anglelintels should be installed with thelonger leg vertical and should alwayshave any space between the verticalleg and the masonry packed withmortar to prevent twisting.

4.6 GroutingWhen masonry is grouted, it is mostimportant that the grout should flowinto all cavities and fully surround allreinforcement. Vibration or roddingshould always be used to ensurecomplete filling. Beforecommencement of grouting, thecores and cavities should be free ofany debris and excessive mortarprotuberances. During the groutingprocess, care must be taken to keepthe reinforcement in its specifiedposition – AS 3700 providestolerances on the reinforcementposition that must be maintained atall times.The height of individual grout liftsdepends on the type of units and thestrength of the mortar joints. If toohigh a lift is attempted or the jointshave not hardened sufficiently, thereis a risk of joints blowing out underpressure of the fluid grout. This willbe less of a risk if the units are ofhigh suction so that the grout stiffensquickly as a result of water beingdrawn into the units.After the cores are filled with groutthey must be topped up tocompensate for shrinkage. This isusually best done approximately 30minutes after initial filling. This top-up should be rodded to ensure that itmerges with the previous grout filling.The most important requirement forthe grout is that it should have atleast 300 kg of cement per cubicmetre, to ensure adequate corrosionprotection for the reinforcement. It isonly necessary to sample and testthe strength of grout if this isspecifically called for in thespecification. (Additional informationon grout is given in Section 3.4.)


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5.1 GeneralTolerances are necessary to allow forinevitable variations in the size ofmasonry products and inaccuraciesin construction techniques. Althoughthere may be situations that requiretighter tolerances, masonry mustgenerally be built to the specifieddimensions within the tolerancesprovided by AS 3700. Two sets oftolerances are provided: for face-workor aesthetic reasons and for structuralperformance. The latter are tighterthan the former.Tolerances are given to cover allaspects of construction:

• Location of elements in plan andelevation.

• Deviation from plumb.

• Bow of surfaces.

• Deviation from horizontal.

• Thickness of bed and perpendjoints.

• Width of cavities.

• Location of reinforcing bars duringgrouting.

5.2 Structural tolerancesThe limits on position in plan andrelative displacement between storeysare necessary to ensure proper loadtransfer through the building.Limitation of the bow in any wall isnecessary to ensure that the wall hasits correct vertical load capacity asdesigned. A method of measuringbow is specified in AS 3700.The deviation from plumb, forstructural considerations, is not toexceed plus or minus 10 mm per 3 m height or 0.05 times thethickness of the leaf, within anystorey. The latter limit will usuallygovern. The limit of 0.05 times thethickness of the leaf corresponds tothe nominal eccentricity that isalways assumed by the verticalloading design rules. These limits ondeviation from plumb are illustratedin Figure 11 for the common wallthicknesses and a range of storeyheights. It can be seen that the limitof 0.05 times the thickness governsin all cases except the 230 mm leaf.The maximum deviation within theheight of the building is limited toplus or minus 25 mm.Limits on joint thickness andalignment are to ensure correctflexural and compressive loadcapacity and the limit on deviationfrom the specified cavity width isprimarily to ensure properperformance of the ties.

5 To l e r a n c e s

5.3 AppearanceQuestions of aesthetics are usually acontractual matter between theparties. However, the followingtolerances should be applied overand above the structural tolerances,for the purpose of ensuring agenerally satisfactory appearance:

• 10 mm maximum deviation fromplumb in any member.

• 3 mm maximum bow in the planesurface of any member.

• 2 mm maximum step between anytwo masonry surfaces that are bothvisible.

• 5 mm maximum deviation of theaverage perpend thickness fromthat specified. (See Figure 12 foran example of perpend thicknessvariation.)

• 8 mm maximum differencebetween the thicknesses of anytwo perpends in a wall.

Other aspects of appearance, such as colour variation, should beresolved where necessary by the useof test panels.

Figure 11. Structural tolerances for out of plumb (within each storey)

Figure 12. Example of perpendthickness variation


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6 Tempo r a r y b r a c i n g

The masonry code AS 3700 gives norules for temporary bracing duringconstruction and there is no generallyaccepted guidance available. Thecode imposes the overall requirementthat masonry under constructionmust be braced or otherwisestabilised as necessary to resist windand other lateral forces, withoutimpairing the structural integrity. It isleft to the builder or designer todetermine how this should be donein each particular case.Once mortar joints have hardened,masonry develops a certain level ofbond strength quite quickly and AS3700 assumes it has reached fullstrength in seven days. It is probablyreasonable (and conservative) toassume that masonry has no bondstrength for the first three days, then50 per cent of its full strength up toan age of seven days. On this basis itis possible to calculate safe workingheights for unbraced masonry, takinginto account wind loading for theheight of building, region,topography, etc.Wind loadings differ widelydepending on the circumstances, and it is therefore not possible to givefigures applicable to all situations.

As a guide, the limiting heights inTable 1 have been calculated using f ’ mt equal to 0.1 MPa (half the coderequirement), for various wallthicknesses and the windclassification scheme in AS 4055(wind loads for housing code). Thisindicates typical figures that might bederived for walls with verticalsupports at 4 m centres and no topsupport (for example, prior toinstallation of a top plate and rooftrusses). Walls of any greater heightshould be propped with temporarybraces until the masonry has gained sufficient strength to be self-supporting.The wind loading code AS 1170.211

requires freestanding walls to bedesigned to resist a pressure of 1.8kPa. Freestanding walls will usuallyhave a membrane or non-masonrymaterial at their base, requiring anassumption of zero tensile strength atthis point. Using these values, Table2 shows height limits calculated for asheltered suburban environment withbuilding heights up to 4 m. Theseheights are for freestanding wallswith no means of support.It should be emphasised that bothTable 1 and Table 2 are intended

Wind classification N2 (W33) Wind classification N3 (W41)

Wall thickness Single leaf Cavity wall Single leaf Cavity wall (mm) height (mm) height (mm) height (mm) height (mm)

90 880 2050 525 1360

110 1050 2600 620 1580

140 2400 N/A 1580 N/A

150 2700 N/A 1700 N/A

190 3050 N/A 1840 N/A

230 8000 N/A 2600 N/A

as guidance. No reliance should beplaced on these figures withoutindependent engineering advice to suit the particular circumstances. It should also be noted that these figures are based on wind loading only and no account is taken of otherpossible loads arising eitheraccidentally or from constructionactivities.The limiting heights shown in Table 2are impractical for most constructionsituations but are quoted here tohighlight the need of walls underconstruction for support against wind loading. Any masonry wall builtto greater heights than those shown in Table 2, with no support fromreturns, intersecting walls or othermeans, should be propped withtemporary braces until it is connectedto the supporting structure as requiredby the design. The values shown inTable 1 can be used as a guide forprops at 4 m centres.For all masonry less than seven days of age, to ensure safety duringperiods of high winds, the vicinity ofany unsupported wall should beevacuated on either side for a distance of the height of the wall plus 1.2 m.

Table 2. Limiting heights for freestanding masonry walls (sheltered suburban environments, building height up to 4 m)

Wall thickness (mm) Limiting height (mm)

90 124

110 186

140 301

150 345

190 554

230 812

Table 1. Limiting heights for masonry under construction (walls with vertical supports at 4 m centres, age 3 to 7 days)


26

7.1 IntroductionIt is essential to identify the type ofstain or deposit before commencingany cleaning operation and tocomplete all the steps of the cleaningprocedure. The appearance of amasonry building can be spoiled bybad cleaning techniques or by theuse of the wrong cleaning agent andit is often difficult to remove thedisfiguring marks left by poorcleaning practices. If there is any doubt about correctcleaning procedures for particularunits, the brick manufacturer shouldbe consulted. For advice on removalof stains other than those covered inthis manual, contact your local ClayBrick and Paver Association orInstitute (for a listing referwww.claybrick.com.au/links).

7.2 Cleaning mortarsmears from masonry

7.2.1 GeneralSkilled bricklayers try to finish theirwork free from blemishes, particularlyon internal face brickwork where acidcleaning methods may be difficult tocarry out late in the job. However,brickwork usually requires somecleaning down.The preferred method is thetraditional one – allow the mortar tojust dry on the surface of the bricksand then wash with water. Thelength of time needed for drying tooccur depends on the type of brickand the temperature – it may take afew hours or a day at most. Once themortar adhering to the surface is dryto the touch it can be scraped orbrushed off. This action will leave athin mortar smear on the surface,that can be removed with the aid ofwater and a stiff brush. All that isrequired is to set aside the first andlast parts of the day for this cleaningtask. Should some of the cleanedbrickwork become soiled again, spotcleaning on the following day willtake care of it. For all brickwork, and particularly for light-coloured orwhite bricks, this is the safestmethod of cleaning.Once the mortar has set and becomehard, the use of water is no longerpractical. In spite of the undesirabilityof having to use acids, either in theirdiluted form or as a component ofone of the many proprietary cleaners,they are then the only practicalcleaning agents. Nearly all damageduring cleaning arises from using toolittle water and too much acid. The colour of most fired clay bodiesis permanent and they themselvesare inert to most chemicals.However, some of them containminute amounts of impurities thatcould react with cleaning chemicals,particularly acids, producingdiscolouration.

7 C l e an i n g o f c l a y ma s on r y

7.2.2 Cleaning with hydrochloricacid

The cheapest and most commonagent for removing mortar that hasbeen allowed to harden is a solutionof hydrochloric acid diluted withwater. It should be noted that somelight coloured cream, grey and brownmasonry units can be moresusceptible than others to ‘burning’by contact with acid. Even thedilutions referred to below might betoo strong for some units and, ifthere is any doubt at all, the productmanufacturer’s advice on a suitablecleaning chemical and methodshould be obtained before using ahydrochloric acid/water solution.The generally recommended dilutionof hydrochloric acid is 1:10 (one partacid to ten parts water) but evenweaker dilutions should be tried first.The acid acts by dissolving both thecement and the lime from the mortar,thus causing it to disintegrate so thatit can be washed away. This action ismore rapid when the acid is stronger,but, with increased concentrations,there is an increased risk of excessiveattack on mortar joints, and ofstaining or ‘burning’ the bricks.Mortars with high cement content arevery difficult to remove once theyhave set and the temptation is toincrease the strength of the acid; thistemptation should be resisted.

Warning: Care is necessary whendiluting concentrated hydrochloricacid to working strength. Select awell-ventilated area, always add theconcentrated acid to the water anduse only earthenware, glass orheavy-duty plastic containers. It isadvisable to wear goggles and rubbergloves when using hydrochloric acidsolutions. Avoid splashing acid ontomaterials adjacent to the brickwork.Polished stone and metal surfacesare likely to be permanently defacedby acid attack and should beprotected by physical shielding or aprotective coating. It is a wiseprecaution to keep such materialsdrenched with water during and aftercleaning in order to minimise the riskof accidental etching by the acid.


http://www.claybrick.com.au/links

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7.2.3 Cleaning external masonryCommence cleaning by rubbingdown the brickwork with a stiff brushassisted by a scraper to remove largelumps of mortar.Whenever possible, avoid cleaning inthe direct sun. Drench the face of thebrickwork with clean water to washoff loose dirt and to reduceabsorption of the cleaning agent intothe bricks. Allow the wall to becomesurface dry.Keep the wall wet ahead of thecleaning operation and apply thecleaning solution to about 4 m2 ofthe thoroughly wet wall. Whenapplying acid to the wall, use a nylonor two-knot brush, not a bristle orwire brush. Scrub the face of thebricks with a brush, or use a mildwater jet to loosen the stain. It isimportant to scrub only the face ofthe bricks and not the mortar joints,in order to minimise acid attack onthe joints. Keep the bricks wet duringcleaning so that neither the cleaningsolution nor the products of itsreaction with mortar droppings aredrawn into the wall. If this precautionis not observed, streaks may be lefton the surface of the brickwork.Wash down each section with a hoseor mild water jet immediately aftercleaning. A water jet is particularlyuseful for removing mortar remnantsfrom highly textured bricks.Repeat the cleaning operation overthe remaining area. Work down fromthe top of the wall and mop offexcess water with a rag or sponge toimprove the job, especially withtextured bricks or raked joints.When the wall has dried, any areathat has been missed should becleaned with the same acid solutionafter being re-wetted. On areas thathave resisted cleaning, the use ofmore vigorous scrubbing is preferableto the use of a stronger acid solution.A second general hydrochloric acidwash rarely improves the quality ofthe brick cleaning and in theseinstances the use of a proprietarycleaning solution is likely to provemore fruitful.

Mortar pigments, and the clay in‘bush’ or ‘fatty’ sands and loams, areboth composed of very smallparticles. Both can leave obstinatemarks on the surface of brickworkeither after absorption from mortarleft in contact with brickwork, or afterseparation from the mortar during thecleaning process. If these marks arenot removed by cleaning withhydrochloric acid, a secondapplication of even stronger acid isnot likely to be effective. Scrubbingthe previously wetted surface with asolution of a commercial detergent issometimes effective in removing claystains and proprietary cleaners willoften remove stains caused by mortarpigments. These stains can be veryresistant to any treatment short ofsandblasting; if nothing is done theywill eventually fade.Where it is practical to do so, theapplication of a neutralising solutionof sodium bicarbonate (as describedin Section 7.2.4 for internalmasonry) is also useful for externalmasonry to minimise the risk ofvanadium staining.

Five Golden Rules For Acid Cleaning1. Wet the wall thoroughly before

any cleaning agent is applied andkeep the wall wet ahead ofcleaning.

2. Select a cleaning agentappropriate to the stain to beremoved and test it on a smallinconspicuous area.

3. Never use hydrochloric acidstronger than 1:10 and preferablyweaker.

4. Scrub the bricks and not thejoints. Vigorous scrubbing is betterthan more acid.

5. Wash down with clean water asthe work proceeds. For a firstclass job mop off surplus waterwith a clean sponge.


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7.2.4 Cleaning internal masonryFor internal masonry the proceduresare essentially the same as thoseoutlined above, but some veryimportant extra precautions need tobe taken for several reasons:(a) Despite pre-wetting the bricks

before using acid solutions, asignificant quantity of thesesolutions will be absorbed intothe body of the bricks. Beingvolatile, hydrochloric acid thenevaporates and the acidic vapourin a closed space will attackmetallic objects and othersusceptible materials.

(b) Excessive pre-wetting increasesthe moisture content of thebrickwork and this can lead topersistent efflorescence.

These problems can be avoided byusing the preferred method ofcleaning brickwork outlined above –scrape off the just-dry mortar andremove the mortar smear using waterand a stiff brush. Acid cleaning willonly be necessary if the mortar isallowed to set.If acid is used, then clean thebrickwork as soon as possible usinga weak solution. Pre-wetting thebrickwork is recommended, but donot soak the bricks – a light sprayjust ahead of the work in progressshould be sufficient.Once the bricks have become surfacedry after the acid clean, apply aliberal coat of a neutralising solutionsuch as 50 g of bicarbonate of sodaper litre of water. Apply this solutionwith a paint-brush or by sprayingand leave it on the wall. Oneapplication is usually sufficient toneutralise the acid left in thebrickwork and a check with a strip ofblue litmus paper should confirm this(see below). If the brickwork is stillacidic, a follow-up bicarbonate ofsoda application is advisable. Thissecond application of the neutralisingsolution should take place not lessthan seven days after the first one.Maintain good ventilation of the areauntil the brickwork has dried outcompletely. Poor ventilation, togetherwith acidic residues in the brickwork,

can cause discolouration on thesurface of susceptible bricks andheavy efflorescence on most bricks or on the mortar joints.The acidity of the brickwork can bechecked with blue litmus paperobtained from chemical suppliers. It stays blue when dipped into aneutral or alkaline solution, but willturn red in contact with an acidicmedium such as brickwork freshlycleaned with acid. Sweat will alsoturn it red because of the acidity ofthe skin, so use clean hands. Dip thelitmus paper into a cup of tap water(it should stay blue but, if it turnsred, use distilled water), spray someof the same water on the surface ofthe brick to be tested and stick thelitmus paper on this wet patch. If it stays blue the brickwork is not acidic.

7.2.5 Other acidsOther mineral acids such assulphuric acid and phosphoric acidshould not be used to clean mortarsmears. Unlike hydrochloric acid,these compounds are not volatile andremain in the brickwork after beingabsorbed. Here they can causeunwanted reactions with both bricksand mortar. In some bricks the saltsproduced from the acids can lead todestruction of the bricks and in othercases the salts cause persistentefflorescence on the surface of the brickwork and can attack themortar joints.

7.2.6 Proprietary cleaningcompounds

There are various proprietarycompounds available for cleaningnew clay masonry or for removingstains. Manufacturers might changethe composition of these products at any time and the user shouldevaluate the cost and suitability ofthose currently available. Themanufacturer’s instructions shouldalways be followed when using these solutions.Some proprietary compounds mightcontain bisulphate, that forms weaksulphuric acid when the dry powderis dissolved in water. The acidity isrelatively low, therefore contact with



29

the skin is less dangerous than withhydrochloric acid, and the solutionacts more slowly on mortardroppings. The disadvantage of thesepowders is that the sulphatesintroduced into the wall may lead toharmful efflorescence.The cleaning solutions that containhydrochloric acid are modified by theaddition of various other chemicals.These additions generally reduce theacidity of the solution so that it actsless vigorously on mortar droppingsthan does an equally strong solutionof hydrochloric acid with noadditives. At the same time, themodifiers make the solutions effectivein preventing or removing variousstains and disfigurements that arenot removed by hydrochloric acidacting alone.

7.2.7 High-pressure water cleaningHigh-pressure water can be used inthe final cleanup after chemicalagents have first dissolved orsoftened the substance to beremoved. However, if the pressure ofthe water is too high and an incorrectjet is used there is considerable riskof damage, particularly to poorquality mortar joints. Figure 13shows an example of mortar jointsdamaged by inappropriate use ofhigh-pressure water cleaning.The following precautions should be observed with high-pressurecleaning:

• Use a maximum pressure of 7000kPa (1000 psi).

• Use a wide fan spray nozzle (15 to20 degrees).

• Keep the nozzle about 500 mmfrom the wall and never closer than300 mm.

• Test the procedure first on asection of wall that is out of view.

Figure 13. Damage to mortar joints by high-pressure cleaning

7.3 Identifying & cleaningstains on masonry

7.3.1 EfflorescenceThe problem: The term efflorescenceis given to a powdery deposit of saltsthat forms on the surfaces of porousbuilding materials such as bricks,mortar and concrete. It is usuallywhite but it may be yellow, green or brown.A temporary efflorescence isparticularly common on newbrickwork as soluble salts aretransported to the surface of the brickby water. The amount ofefflorescence that occurs is directlyrelated to the amount of water in thebricks and their drying time – themore water there is in the bricks andthe longer it is there, the morechance salts will have to dissolve init and be transported to the surfaceduring the drying process.The salts that appear as efflorescenceenter the wall from various sources.Extensive experience in Australiashows that new bricks seldomcontain soluble salts, however suchmay not be the case with brickssalvaged from demolished structures.Ground waters that are naturally saltbearing, or that pick up gardenfertilisers, can be drawn into bricksbelow damp-proof courses. If damp-proof membranes are faulty, thesesalts pass into higher levels in the wall.


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Efflorescence on new brickwork maybe unsightly (see Figure 14), but itwill not cause damage unless itpersists for a long time. Persistentefflorescence should be taken as awarning that water is entering thewall through faulty copings, flashingsor pipes. If allowed to continueunchecked, the salts carried to theface of the wall may eventuallyattack and cause deterioration ofsome bricks.

The remedy: Efflorescence can beminimised by laying dry bricks andby providing good ventilation tospeed up the drying process after thebricks have been laid. The salts thatcause efflorescence are soluble inwater and will be washed fromexternal walls by rain, howeverhosing down affected surfaces atintervals will speed this process. Oninternal walls, follow a sequence ofbrushing and washing down withfresh water. Forced ventilation andheating of the premises may benecessary to ensure drying duringcold winter months.Acid or alkaline treatments do moreharm than good because they add tothe total salt content of the wall. Theapplication of kerosene or oil doeslittle or nothing to hide theefflorescent salts and prevents theirsubsequent removal by brushing andwashing.

7.3.2 Vanadium stainsThe problem: Light-coloured bricksoften contain traces of vanadiumsalts that can appear as a yellow,green or reddish-brown discolourationon the bricks. Hydrochloric acid candarken this discolouration, making itmore difficult to remove. The stainstake the form of a thin film on thesurface of the brick and are notharmful. Most often the vanadiumsalts weather away, however theirremoval can be hastened bychemical treatments.It is essential that deposits ofvanadium salt be removed beforeusing hydrochloric acid on mortarresidues and that the acid used inthese circumstances be as weak aspossible. Some of the proprietarymortar-cleaning solutions claim to beeffective in combating this problembut the best procedure remains touse the water-wash technique onjust-dried mortar rather than to useacid cleaners. Bricks that are liable tovanadium staining usually give awarning by showing the stain ontheir surface after they have becomewet and been allowed to dry out.This commonly occurs before thebricks are laid.Keeping the total moisture content ofthe brickwork low, together withencouraging quick drying, will reducethe amount of salt that comes to thesurface.The remedy: The most effectivechemical treatment must be found bytrial. Oxalic acid, hypochloritebleaching agents, caustic soda orcaustic potash and some of theproprietary cleaners are effective indifferent cases. These stain-removingchemicals should always be appliedto dry bricks.Alkaline treatments are to bepreferred, when they work, becausealkaline vanadium salts are whiteand relatively soluble in water. Bycontrast, acidic salts of vanadium arecoloured and thus more visible.When the acid cleaning procedure isused to dissolve the vanadium salts,the salts are drawn back into thebody of the brick and made invisible.


Figure 14. Efflorescence from calcium being released from mortar


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However, subsequent wetting anddrying might bring the coloured saltsback to the surface. The alkaline wash after the acidtreatment is intended to change thecoloured acidic salts to white alkalinesalts. The wash should alsoneutralise the surface of the brickand thus prevent any further saltsthat are drawn to the surface frombecoming acidic. Quick drying of thetreated surfaces usually helps thesuccess of this procedure.Details of the various techniques fordealing with vanadium stains are asfollows:(a) Oxalic acid. For the oxalic acid

treatment, brush the affectedsurface with a solution containing20 to 40 g of oxalic acid per litreof water. The action is more rapidif the solution is applied hot.When the stain has beenremoved from the surface,complete the treatment byapplying a solution of 10 g ofwashing soda per litre of waterand allow this solution to remainon the wall. This neutralisationstep is most important – itprevents unwanted further actionby the oxalic acid.

Warning: Oxalic acid is a poison – it should be stored and used with care.

(b) Hypochlorite treatment. For thehypochlorite treatment, applyeither household bleach based onsodium hypochlorite or a solutionof pool chlorine (100 g per litre ofwater) to the wall.

(c) Alkaline treatment. For thealkaline treatment, wash the wallwith a solution of caustic soda orwashing soda (100 g per litre ofwater). Use the correspondingpotassium salts if available, asthey are less likely to causevisible secondary efflorescence. If such efflorescence appears,wash it off with clean water.

Warning: These alkalis arehighly corrosive if in contactwith the skin or eyes. Thewearing of protective clothes,including eye protection, is strongly recommended.

(d) Poultice techniques. Very heavyvanadium stains, or ones thatpersistently recur, can usually beremoved by a poultice technique.Use a proprietary product ormake a paste using a 10 per centsolution of sulphuric acid as theactive agent. The paste can bemade from fine-grained,chemically inert filler such askaolin, bentonite, diatomaceousearth or talc mixed with thecleaning agent.

(e) Proprietary cleaners. Someproprietary products have beenfound to prevent the appearanceof vanadium stains or reduce theirseverity when they are used forremoving mortar. However, thesuppliers do not usuallyguarantee the success of theirproducts. These cleaners can also be used to remove vanadiumstains that appear after mortarhas been removed using otherprocedures. In this case, a follow-up neutralising treatmentwith a solution of 15 g of causticsoda per litre of water isrecommended.

7.3.3 Manganese stainsThe problem: A dark-brown to violetdiscolouration can occur on bricksthat have been coloured grey orbrown either by an addition ofmanganese dioxide or by havingmanganese naturally present in theraw materials. The stain occurs alongthe edges of the bricks, or in thecentre of the face of lighter-firedproducts. It can also appear aroundmortar droppings on bricks.

The remedy: Manganese stains can be quickly removed by using anappropriate proprietary cleaningproduct. The solution should be applied to the dry surface and allowed to react until the staindissolves. It should then be washed off with water. Do not neutralise with alkalis as their reaction with the dissolved stain could produce further staining.

7.3.4 Stains from mortar ingredientsThe problem: The danger of stainingfrom clay in the mortar sand, and from colouring materials added tomortar, has been discussed in Section 7.2.3.The remedy: Vigorous scrubbing with a solution of a commercial detergent,followed by a thorough wash downwith fresh water can be tried, but isseldom fully effective against either type of stain. Prevention of such stains by the careful selection and use of mortar materials is the bestcourse of action. Weathering over aperiod of time, or the use of aproprietary cleaner, will fade the stains appreciably.


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8 Te s t i n g o f ma s on r y

8.1 GeneralAS 3700 provides two methods ofassessing the strength of masonry –compressive strength and flexuralstrength. Their use depends on thetype of masonry structure and thecircumstances surrounding thetesting. Apart from researchapplications, tests may be carried out to:

• Assess the quality or compliance ofmasonry during construction. Thisis only required when designstrengths higher than the defaultare used and the masonry isdeclared as Special Masonry.

• Determine design characteristicstrengths for masonry constructedwith new or unfamiliarcomponents. This application israre and is outside the scope ofthis manual.

• Assess the adequacy of a structurethat has failed or where there issome doubt about its strength. This situation is outside the scopeof AS 3700, although theprocedures given there can beused if appropriate.

When tests are carried out, thematerials and bricklayers should bethe same as those used on the job,so that in every respect the testspecimens represent the masonryactually being constructed on site. AS 3700 defines the layingprocedure for test specimens in orderto simulate the normal laying ofmasonry. The bricklayer shouldpause for a time between stringingout the mortar and bedding the unitson it because the run of mortarstrung out in normal work would belonger than that required for a typicalsample of test specimens.

The timing of the operation isimportant, to allow water transferfrom the mortar to the lower courseof units before the upper course isbedded down. It is also important(particularly for flexural tensile tests)that the joint treatment for the testspecimens should be the same asthat used for the masonry in the job.

For both compressive and tensiletests, the testing is carried out at anage of seven days. When specimensare constructed specifically fortesting, wrapping them in polythenesheeting immediately afterconstruction promotes curing and isrequired by AS 3700.

8.2 Quality control testingof special masonry

Whenever a designer uses a higherdesign strength than the defaultvalue given in AS 3700, thecorresponding masonry is classifiedas Special Masonry. This means thatsite testing for quality controlbecomes mandatory for that masonryand must be carried out at theprescribed rate. This testing isusually for either flexural tensile bondstrength or compressive strength andwould rarely be required for both onthe same job. The number ofspecimens in a sample is at leastthree for compressive strength and atleast six for flexural tensile strength.The procedures for testing aredescribed in Sections 8.3 and 8.4.All assessment of test results isbased on the average strength of thetest sample.The sampling rate is the minimum of:

• one sample per storey height

• one sample per 400 m2

• two samples

Target strengths are given in AS3700 for compression and tension as follows:

• Compression 1.4 f ’m

• Tension 1.7 f ’mt

Where f ’m and f ’mt are the designcharacteristic compressive andflexural strengths respectively. Thereason why the multiplier for tensionis higher than for compression is thatthe inherent variability of tensilestrength is higher than forcompressive strength.

The test strength is the averagestrength of the specimens in asample. For control of SpecialMasonry the test strength for eachsample is calculated and if the


33

average of the last four samples fallsbelow 90 per cent of the target, thenaction must be taken to correct theproblem. Clearly, while normalvariation is expected, if successivesample strengths fall below the targetit would be prudent then to checkthe construction practices forcompliance with the specification,rather than waiting for the codecriterion to be violated.

The best way to monitor test resultsis to maintain a control chart on siteand, as each test strength becomesavailable, to plot it on the chart,along with the average of that testresult and the three preceding ones.Lines representing the target strengthand 90 per cent of the target shouldalso be drawn on the chart.

The sample chart in Figure 15 shows six separate test sampleresults (A to F) from a hypotheticaljob. The design characteristic tensilestrength (f ’mt) is 0.4 MPa, giving atarget strength of 0.68 MPa. Eachsample average is shown, as well asthe running average of four samples(or less in the case of the first three samples).

Although sample B has strength wellbelow the target, the average of Aand B is still above 90 per cent sothere is no immediate cause forconcern. However, when sample Ccomes in even lower and brings theaverage of A, B and C below the 90per cent line, then the causes shouldbe investigated and remedial actiontaken. Sample D gives a higherresult, trending in the right direction,but with an average (now of foursamples) still below the 90 per centline. In this hypothetical situation theimprovements are sustained,resulting in a high strength forsample E and leading to the runningaverage being restored to anacceptable level at sample F.

Note that every individual sampleaverage is above f ’mt and thereforenone of these samples fails thecriteria for compliance (see Section8.5). This is the purpose of qualitycontrol testing – to correct adversetrends such as that displayed bysamples A, B and C in this examplebefore they cause a situation wheremasonry is liable to rejection.

8.3 Compressive strengthtesting

For compressive strength testing thespecimens are stack-bonded prismsand are required to have a height-to-width ratio between two and five,with at least three courses in thespecimen. This latter requirement isto ensure that there are at least twomortar joints in the specimenbecause of the significant effect thatjoints have on compressive strength.It is also possible to derivecompressive test specimens fromundamaged portions of beams thathave been tested for flexural strengthand by cutting pieces from a wall.The last option would be used if thestrength of constructed masonry wereto be assessed and there were notest specimens made at the time ofconstruction with the same materials.Laboratory specimens must be curedby wrapping in plastic sheeting forseven days before testing. Testing iscarried out in a compression testmachine with plywood end caps onthe specimen to minimise platenrestraint and even out anyirregularities in the surface. Anaspect ratio factor is applied to themeasured strength to eliminate theeffects of platen restraint. AS 3700permits the rejection of abnormalresults, if they meet certain criteria,before calculation of the samplestrength.

Figure 15. Example quality control chart


34

8 Te s t i n g o f ma s on r y

8.4 Flexural strengthtesting

For flexural tensile strength thespecimens are stack-bonded prismswith between three and sevencourses. The same type of specimencan be used for both compressivestrength and tensile strength tests,thus simplifying the job of specifyingconstruction of test specimens.The bond wrench method of testing(see Figure 16) has almostcompletely superseded the bondbeam test method, although the latteris still permitted by AS 3700. Usingthe bond wrench, the strength ofeach joint in the specimen isindividually determined. The samplestrength is then the average of theindividual joint strengths.Again it is permitted to rejectabnormal test results and acharacteristic strength is onlycalculated when the aim is to derivea design strength, not for complianceor site control test purposes.Although it is possible to test beamspecimens and then use theremaining pieces for bond wrenchtests, this is not often done.

In principle, the bond wrench appliesa uniform moment to a bed joint,with negligible superimposedcompression. It therefore measuresthe modulus of rupture of the joint.This moment is converted to aflexural tensile stress at the extremefibre, using the section modulusbased on the manufacturingdimensions of the units. This stressis equivalent to the flexural tensilestrength property used in design.It is also possible, and useful whenthe strength of constructed masonryis to be assessed, to use a bondwrench to measure the strength ofjoints directly in a wall. Access to thetop of the wall is required and theperpend joints at both ends of thebed joint to be tested are cutthrough. The bond wrench is thenattached and used to 'peel' off thebrick. Subsequent tests can beapplied to adjacent joints, followedby those in the courses below.The specification of the bond wrenchapparatus was more closely definedin the 1998 edition of AS 3700 thanin the previous edition. It isimportant to check that any bondwrench used for testing actuallyconforms to the specification.

8.5 Assessment ofcompliance

The results of site tests are used forthe assessment of compliance ofSpecial Masonry, as well as forquality control. Each individual testsample represents a segment ofmasonry on the job and thisrelationship should be tracked andrecorded on site. Then if the result ofany sample falls below a specifiedstrength level the whole of themasonry represented by that sampleis deemed not to comply with AS 3700.If the test strength of any sample isbelow the design characteristic value(f ’m or f ’mt as appropriate) then themasonry represented by that sampleis deemed not to comply with thestandard. What happens then is acontractual matter, and variousoptions are discussed in Section 8.6.

Figure 16. Schematic arrangement of bond wrench test

Clamp

Applied load

Clamp

Support

Load read-out


35

At first it might appear strange (evengenerous) that the requirement is tocompare an average strength with acharacteristic value but the method isbased on an assessment of the risksinvolved and is designed to minimisethe chances of good masonry beingrejected and forcibly demolished.The sample chart in Figure 17 showssix separate test sample results (A to F) from a hypothetical job. Thedesign characteristic strength (f ’mt) for this job is 0.4 MPa. Each sampleaverage is shown, and also the targetstrength (0.68 MPa) for qualitycontrol.Both samples A and B pass thecriterion for compliance but, whereasA meets the target for quality control,B falls below and should be a causefor concern. The downward trendcontinues and sample C fails thecompliance criterion because itsstrength is below f ’mt.

Improvements are made and sampleD satisfies the compliance criterionbut is still well below the targetstrength, indicating that furtherimprovement in site practices ormaterials is necessary. The upwardtrend continues and sample Ecomplies but is still below target.Further improvements bring sample Fabove the target strength.As a result of this series of tests, onlysample C fails the compliance testand all the masonry associated withthis sample is deemed not to complywith AS 3700. The appropriateactions to deal with this failure aredescribed in the next section.

8.6 When masonry doesnot comply

When a test sample fails thecompliance assessment the whole ofthe masonry represented by thesample is deemed not to comply.What happens when masonry doesnot comply with the code is acontractual matter between thebuilder and his client and is thereforenot specified by AS 3700. Options tobe considered include the following:

• A design check to see if theparticular masonry element (withreduced strength) still has sufficientdesign resistance to withstand thedesign loads. Many masonryelements are over-designedbecause a uniform specification ofwall thickness and materials isused throughout the job.

• Carrying out further tests onspecimens constructed on site toassess their strength and identifyreasons for failure of the initial test sample.

• Carrying out tests of the masonrystrength within the wall (by in situbond wrench or by cuttingspecimens from the work) – see below.

• Strengthening the construction byretrofitting.

• Demolishing and rebuilding themasonry.

Where problems arise in masonryconstruction or where doubt existsthat the masonry strengths meetthose required by the design,guidance is given in AS 3700(Appendix J – see Amendment 2) forcarrying out tests on the constructedmasonry. This will usually involveobtaining test specimens directlyfrom the wall, which can be for

Figure 17. Example compliance assessment chart

flexural or compressive strengthtesting. Use of the bond wrench for testing in situ was discussed inSection 8.4.

It is also possible to sample mortarand carry out a test for cementcontent, with the relevant compliancecriterion provided by AS 3700.However, testing for cement contentshould be used with care because itoften bears little relationship to theflexural tensile strength of themasonry. It is much more relevant to durability, for which there are noestablished performance criteria. In many cases, it is preferable to test the required property (such astensile strength) rather than thecement content.


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1. Building Code of Australia Volume 2: Class 1 and Class 10 Buildings (HousingProvisions), Australian Building Codes Board, Canberra, 1996 (as amended 1-Jan-2000).

2. AS 3700, Masonry Structures, Standards Australia, Sydney, 1998.

3. AS 3700 Supplement 1, Masonry Structures – Commentary, Standards Australia,Sydney, 1999.

4. Manual 9, Detailing of Clay Masonry Walls, Clay Brick & Paver Institute, Sydney,May 2000.

5. AS 3972, Portland and Blended Cements, Standards Australia, Sydney, 1997.

6. AS/NZS 2904, Damp-proof Courses and Flashings, Standards Australia, Sydney, 1995.

7. AS/NZS 2699.1, Built-in Components for Masonry Construction, Part 1: Wall ties,Standards Australia, Sydney, 2000.

8. AS/NZS 2699.2, Built-in Components for Masonry construction, Part 2:Connectors and accessories, Standards Australia, Sydney, 2000.

9. AS/NZS 2699.3, Built-in Components for Masonry Construction, Part 3:Lintels and shelf angles (durability requirements), Standards Australia, Sydney, 2000.

10. AS 4055, Wind Loads for Housing, Standards Australia, Sydney, 1992.

11. AS 1170.2, SAA Loading Code, Part 2: Wind loads, Standards Australia, Sydney, 1989.

9 Re f e r e n c e s


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