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The Brick Cleaning Manual 2014

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The Brick Cleaning Manual
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Page 1: The Brick Cleaning Manual 2014

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Published 2008

ISBN 0-947160-12-4

This publication, its contents and format are copyright of the Clay Brick and Paver Institute, trading as Think Brick Australiaand may not be reproduced, copied or stored in any medium without prior written authorization from the Institute.

Important DisclaimerThis may affect your legal rights:

The Clay Brick and Paver Institute Limited is a voluntary body whose charter is amongst other things the promulgationof educational information to assist persons undertaking the cleaning of bricks and pavers.

The information contained in this manual is for general guidance only and does not relieve any person reading the manual fromcarrying out their own due diligence to ensure that the methods they adopt and materials/chemicals they use for cleaning bricksand pavers are appropriate and safe. Further, all methods adopted and/or materials and chemicals used, whether containedin or referred to in this manual are required to comply with all laws, statutes and regulations in force from time to time.

While the content of this manual is based on information from sources which are considered reliable, the Clay Brickand Paver Institute, its officers, employees and consultants do not represent, warrant or guarantee expressly or implied,that the information contained in the manual is complete or accurate.

The manual is not designed, nor does it replace the service of professional advisers. Neither the Clay Brick and PaverInstitute, its officers, employees, and consultants shall be liable in any way for any loss or damage, howsoever arising(whether in negligence or otherwise) out of or in connection with the use of the contents of this manual.

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Table of contents

Introduction  2Section 1: Design and construction  3

Section 2: Cleaning mortar residues  5

  A clean start 5

  Acids – the basics 5

  Cleaning – the basics 7

  Procedure for hand cleaning 7

  High pressure water jet cleaning 8

  Cleaning internal brickwork 11

Section 3: Stain removal  12

  Acid burn (Iron oxide stains) 12

  Calcium stains 14

  Vanadium stains 16

  Efflorescence 18

  Graffiti and paint 20

  Iron and welding spatter 20

  Oil, bitumen and tar stains 21

  Organic growths 21

  Smoke stains 22

  Soil and grime 23

  Timber stains 23

  Manganese stains 24

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This manual covers the cleaning of clay masonry only andshould not be applied to other masonry materials.

In addition to detailing cleaning methods, guidanceis given on design and construction techniques tominimise staining and the need for subsequent cleaning.

Simple precautions will help avoid staining and

disfigurement and are always preferable to later cleaning.The methods detailed here are based on successful practicesimplemented over many years. However tests to determinethe most effective technique should always be conductedbefore undertaking any cleaning or stain removal process.

Introduction

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Bricklaying

Mortar extruded from masonry jointsduring laying should be cut off with atrowel. In this way a clean cut can be madewith little smearing of the unit face.

On completion of laying and joint tooling,

mortar smears on the work face should beremoved by dry brushing.

Wet sponging of the mortar joints is acommon practice with smooth face bricks.Although this creates a smoother jointfinish, it smears a cement-rich mortar filmover the brick face that often developsinto staining.

Cleaning cavities

Cavities can be cleaned by hosing at the endof a day’s work. Temporarily leave bricksout at the wall base to enable mortar to behosed clear of the cavity.

Take care to ensure that mortar does notset on masonry below the base of the cavity.This is best done by thoroughly hosing themasonry below.

Concrete droppingsMasonry supporting reinforced concreteslabs and beams is frequently disfigured bydroppings and spattering from the concretepour. If these deposits are allowed to setit is sometimes impossible to rectify thedamage. Protection is best achieved bycovering the walls with plastic sheeting.Where this is not done, any deposits on thewall must be thoroughly hosed off beforethey set.

Copings, sills, weathering

Stormwater should be shed so as to clearthe masonry immediately below. Copingsand sills should project at least 10 mmbeyond the wall face at the underside ofthe sill or coping. Sills should be angledto properly shed water.

Where downpipes have not been installedwater from the guttering should be divertedaway from the brickwork.

In-built elements

In-built elements should slope away frommasonry. The soffit of major elements suchas balconies should be provided with adrip mould. It is desirable for all roofs to be

provided with sufficient overhang to protectthe wall below.

Mortar additives

Some mortar additives if used incorrectlymay create problems during thebrick-cleaning process, examples being:

•  Air-entraining agents such as Bycol orsimilar used to improve the workability

of mortar. Its overuse creates a highlyporous mortar that is easily erodedduring cleaning.

•  Water modifying agents such as Dynexor similar, used to retard the absorptionof water from the mortar into the brick,is extremely difficult to remove from thebrick if left on for more than one totwo weeks.

Section 1: Design and construction

Consideration should be given during design and construction to thefollowing matters to avoid or minimise clay masonry cleaning problems.

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•  Up to ten percent of naturally-occurringclay in bush sand is useful in enhancingthe plasticity of the mortar. However claycontent around 15 percent is detrimentalto the mortar as excessive shrinkage willoccur, creating cracks within the mortarand at the mortar/brick interface.

•  Sugar used as a mortar retarder is notrecommended as it creates a hard mortarsurface that inhibits the absorption of

acid, thereby preventing the softeningand dissolution of the cement whencleaning mortar residue (the use of sugarin mortar does not comply with therelevant Codes and Standards).

Paint overspray and splashing

Extreme care is needed to avoid paint andtimber stains being splashed onto masonry.Dried paint is extremely difficult to remove,

therefore prevention is the best cure.

Rain interruption

When rain interrupts bricklaying – or isexpected overnight – protect the top of thenewly laid wall with plastic sheeting.

See also calcium stains in Section 3.

Retaining wallsThe rear face of retaining walls should bewaterproofed by such methods as cementrendering, coatings of Cemstick, use ofa plastic sheet membrane or bituminouscoating. This will prevent the migrationof soluble salts through the wall. Properdrainage should also be providedbehind the wall.

ScaffoldingScaffolding planks should be laid at least150 mm clear of the wall, allowing mortardroppings to fall clear instead of buildingup on the plank and disfiguring the wall.At the end of each day’s work – or whenrain interrupts work – the plank nearest thewall should be propped on edge to preventmortar which may have collected on itbeing splattered onto the wall.

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A clean startThe cleaner the bricklayer leaves the wallthe easier the cleaning task will be. Themajority of mortar residues and smearsshould be cleaned before they set. However,in most cases some additional cleaningwill be required to completely remove themortar residue.

Acids – the basicsSafety requirements

All acids and proprietary cleaners aredangerous. Users are required by law to:

•  Obtain a copy of the manufacturer’sMaterial Safety Data Sheet (MSDS) forevery chemical used in the conduct oftheir work and to only use the product inaccordance with the instructions in theMaterial Safety Data Sheet.

In particular you are reminded thathydrochloric acid is classified as a corrosiveS6 poison. All steps should be taken tocomply with the requirements for its usein the Material Safety Data Sheet.

To avoid personal injury users should always:

•  Wear all necessary safety equipmentdetailed in the Materials Safety Data

Sheet including but not limited togoggles or face mask, gloves, andprotective clothing as advised.

•  Pour acids into water – this avoidssplashes of highly concentrated acidonto the operator.

•  If an acid or proprietary cleaner issplashed onto the skin, it should beimmediately swabbed with clean wateror more effectively with a solution ofbicarbonate of soda and water that willneutralise the acid. Medical attentionshould be sought with respect to anyinjury arising from the use of chemicals.Chemical spills are required to be treatedin accordance with the advice containedin the Material Safety Data Sheet.

•  For transport and environmental care ofsuch chemicals, users should refer to theirState regulatory authorities.

Section 2: Cleaning mortar residues

Typical wall after brick laying

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Acid concentrations and cautions

The traditional masonry cleaning chemicalis hydrochloric acid, (also known asmuriatic acid or spirits of salts). Its mainfunction is to put portland cement intosolution, that is, dissolve the cement inthe mortar mix. It has few other uses andin many stain situations SHOULD NOTBE USED.

The recommended maximum strengthfor light coloured clay bricks is 1 part acidto 20 parts water, and the recommendedmaximum strength for all other clay bricksis 1 part acid to 10 parts water.

Note: This point must be strictly adheredto particularly for bricks manufactured inQueensland. Their raw materials naturallycontain large amounts of iron oxide,sometimes just below the surface. The useof acid solutions stronger than 1 part acid to

20 parts water can dissolve these particlesand create iron oxide staining. Removal ofthese stains is treated in Section 3.

Proprietary masonry cleaning solutionsare available. The manufacturer’srecommendations must be adheredto strictly.

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Cleaning – the basicsCleaning techniques may involvehigh-pressure water jet equipment orhand methods. Both are detailed later inthis section. Whatever technique is used,the following requirements mustbe observed to ensure that additionalstaining problems are avoided:

Saturate the wallThe brickwork must be thoroughly wettedby hosing before any acid solution is appliedand kept wet ahead of the acid application.The area to be cleaned must be saturatedas well as all brickwork areas below. Thehose should be trained upon the wall untilthe brick suction is exhausted.

If the wall appears to be drying on thesurface, reapply water until ready to apply

the cleaning solution.Failure to completely saturate the wall isa major cause of cleaning stains. Cleaningsolutions containing dissolved mortarparticles will be drawn into a dry masonrywall, causing further staining. Furthermoresaturating the wall keeps the acid solutionon the face of the masonry where themortar smears are present.

Recommended acid strengths are based

on application to a saturated wall and itis a myth to consider that pre-wetting‘weakens’ the acid.

Note: This point must be strictly adheredto for bricks manufactured in Queensland.Failure to saturate the wall allows acidsolutions to react with the iron oxide andcreate iron oxide staining. Removal of ironoxide stains is treated in Section 3.

Acid applicationApply the acid solution and leave to standon the wall to allow the chemical actionto take place, this could take up to 3 to 6minutes, however for bricks manufacturedin Queensland and Western Australia alesser time is advised or secondary stainingcan occur.

Hose off 

If the acid is left on the wall too long it canbe absorbed into the brickwork and maycause staining.

It is extremely important to thoroughlyhose off the wall as the work proceeds.The acid solution and debris cleaned offthe wall must not be allowed to dry on thewall. Weather conditions, location of themasonry, and the suction of the bricks will

affect the timing of the hosing off. Generallytwo to six square metres should betreated at a time.

Procedure forhand cleaningHand cleaning was the most widely usedmethod of cleaning clay masonry walls priorto the advent of the high pressure water jet

equipment. This method is very appropriatefor small jobs or where the use of highpressure water jet equipment may causefurther problems.

1.  Wait for mortar to harden. It is possibleto start cleaning 24 to 36 hours aftercompletion of masonry work, dependingon the type of brick and the weather(drying) conditions.

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2.  Remove all large mortar particles withhand tools – a wooden paddle, brickor chisel – before applying water orcleaning solutions. This ‘pre-cleaning’is an important part in cleaning newmasonry. Don’t expect acid and/orwater alone to remove large particlesof hardened mortar.

3.  Mask and otherwise protect adjacentmaterials such as metal, glass andwood, as recommended by product

manufacturers.

4.  Care should be taken to identify andremove any vanadium staining onthe brickwork prior to applying thesolution of hydrochloric acid, as it mayturn the vanadium black and make itmore difficult to remove. For furtherinformation regarding removal ofvanadium stains refer to Section 3.

5.  Thoroughly wet the face of the wall

with clean water. All areas to be cleanedmust be saturated as well as masonryareas below.

6.  Use a brush or spray to apply the acidsolution to the saturated wall. Startcleaning at the top of the wall. Covera small area.

7.  Allow the solution to remain on the wallfor sufficient time for the reaction to takeplace. This could take up to 3 to 6 minutes.

Then scrub vigorously with a scrubbingbrush. Scrub bricks not joints.

8.  Rinse thoroughly as small areas are beingcleaned. To slow evaporation, work aheadof sunshine. These ideal conditions allowwalls to dry soon after being washed,permitting the operator to observe if allstains are being removed before movingtoo far ahead.

High pressurewater jet cleaningHigh pressure water jet cleaning can be usedon clay masonry but the following simpleprecautions must be taken so that the bricksand the mortar joints are not damaged bythe process.

Caution: Turbo or rotary head attachmentsdamage brickwork and are not

recommended.Caution: Test clean a sample area todetermine the effectiveness of the cleaningcompound and the technique, and to checkthe wall for possible damage caused bythe system.

Allow mortar to harden. Cleaning withhigh water pressure should not start beforemortar is at least three days old.

1.  Remove all large mortar particles withhand tools – a wooden paddle, brickor chisel – before applying water orcleaning solutions. This ‘pre-cleaning’is an important part in cleaning newmasonry. Don’t expect acid and/orwater alone to remove large particlesof hardened mortar.

2.  Mask and otherwise protect adjacentmaterials such as metal, glass andwood, as recommended by product

manufacturers.3.  Care should be taken to identify and

remove any vanadium staining onthe brickwork prior to applying thesolution of hydrochloric acid as it mayturn the vanadium black and make itmore difficult to remove. For furtherinformation regarding removal ofvanadium stains refer to Section 3.

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4.  Thoroughly wet the face of the wallwith clean water. All areas to be cleanedmust be saturated as well as masonryareas below.

5. When the suction of brick is exhausted,apply the appropriate cleaning solution,starting at the top of the wall workingin small areas. The solution may beapplied to the wall with a masonrycleaning brush, soft broom or low

pressure (maximum 40 psi) sprayer.  Applying acid solutions under high

pressure is not recommended. Thepractice is harmful to the operator,to adjoining property and can drivethe cleaning solution further intothe masonry than is necessary forsurface cleaning, possibly causingfurther staining.

6.  Allow the cleaning solution to remain

on the wall to allow the chemicalreaction to take place, this couldtake up to 3 to 6 minutes, however forbricks manufactured in Queenslandand Western Australia a lesser time isadvised or secondary staining can occur.

Damage to bricks caused by incorrect

use of high pressure water jet cleaning

Damage to ironed mortar joint

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7.  Wash the wall with high pressure waterfrom top to bottom so all dissolvedmortar particles will be completelyflushed from wall surfaces.

  The maximum pressure at the pumpshould be kept low, around 7000 to8000 kPa (1000 to 1200 psi), to preventdamage to either the masonry units orthe mortar.

  The concentration of power with

which the water jet strikes the wall isa function of the flow in the hose, thepressure, the type of nozzle and thedistance from the nozzle to the wall.

  A straight or zero degree water jet shouldnever be used. A spray angle of 15 degrees,called a fan jet, will allow the operatorto concentrate the pressure on the bricksand not on the joints. The jet shouldgenerally be 500 mm from the wall

and never closer than 300 mm forlocalised patches.

  Pressure cleaning should be carried outin ‘runs’ from the top of the wall down,to rinse down debris during cleaning.The width of a run is usually 1 to 1.2metres, and should only be as wide asthe operator can clean while keepingfull control of the pressure gun. The gunmust be kept moving: surface abrasionwill occur if it pauses in one spot.

  Turbo head water jets are notrecommended as there is a highpotential for damaging the bricksand/or mortar by the concentratedforce of the water.

8.  Any lumps or smears remaining afterinitial treatment will require anotherscrape, followed by wetting, acidtreatment and pressure cleaning. Thepatience of double cleaning on difficultstains will be rewarded with a firstclass finish. It also eliminates the riskof eroding bricks or joints, the mainobjections to the water-blastcleaning method.

9.  When all cleaning is finished, go backand rinse loose sand and dirt from theeaves, walls and windows. Once thewalls begin to dry, check to see if anyfurther cleaning is required.

Caution: If the mortar joints or the bricksare being damaged, either the pressureis too high or the water jet is too closeto the wall.

Caution: Before cleaning dry pressed

bricks the manufacturers advice should beobtained as the use of high pressure watercleaning is not recommended.

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Cleaning internalbrickworkUsing hydrochloric acid to clean mortardeposits on internal masonry requiresspecial care. The work should be done beforethe building is enclosed to ensure maximumventilation and exhaustion of acid fumes.

Frequently this procedure is not followedand the masonry is cleaned at thecompletion of the building, making itimpractical to use large quantities ofwater. The result can be acid fumesflowing from the masonry for some timeafter occupation, attacking metal doorfurniture, light fittings, steel furniture,exposed metal grid ceilings and othermetal components.

In addition to early cleaning, the followingprocedures are recommended when

cleaning internal brickwork:

•  Use a proprietary cleaner containing anacid inhibitor that reduces fumes fromhydrochloric acid. OR

•  After washing down, apply a neutralisingwash consisting of 65 grams of SodiumBicarbonate per litre of water. Leave thison the wall. If acid fumes are suspectedto be coming from the wall, test usinglitmus paper. Moisten a strip and apply

it to the wall. If the blue paper turns red,acid is present and a neutralising washshould be applied.

Quite often stains occur on brickworkfrom the failure to follow correct cleaningprocedures when removing mortar residue.Stains are aesthetic blemishes and donot affect the structural adequacy of thebrickwork and are generally easily removed.

The correct identification of stainson brickwork is a first step in theremoval process.

Testing on one or more small areas isthe safest way to determine the correctchemical solution and technique to removea particular stain. This must take place wellahead of final cleaning as it will usually notbe possible to assess the effectiveness ofthe test clean until the masonry dries.

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Acid burn(Iron oxide stain)This is a yellow, orange to brown rust-likestain. It is most obvious on cream bricksbut can similarly occur on darker colouredbricks. Iron oxide stains frequently resultfrom the incorrect use of hydrochloricacid on clay masonry.

This stain is commonly called ‘acid-burn’because the reaction between hydrochloricacid and iron oxides in the brick and/ormortar sand causes the formation of ironoxide or rust on the face of the brick andcan also leach into the mortar joint.

The most common causes of incorrecthydrochloric acid cleaning leading to ironoxide staining are:

•  Failing to thoroughly pre-wet thewall and keep it wet ahead of thecleaning operation.

•  Failing to thoroughly hose downeach four to six square metres of thecleaned area.

•  Using a hydrochloric acid solutionstronger than 1 part acid to 20 partswater on light coloured bricks, orstronger than 1 part acid to 10 partswater on other bricks.

•  Too often the acid solution is not givensufficient time to act properly, usuallyresulting in the operator increasing theacid strength.

Pre-wetting and frequent washing off isdesigned to prevent undue penetration ofthe acid into the brick and mortar wherefurther reactions and staining often occur.Window sills and corners require particularattention with pre-wetting as the waterreadily runs off instead of being absorbed.

Acid burn on face brick work

Acid burn on light coloured bricks

Section 3: Stain removal

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Removal technique for acid burn

Phosphoric acid

1.  The application strength and durationwill vary. As a guide, use a mixture of1 part phosphoric acid to 6 parts water.

2.  Apply by brush or spray to the drywall and allow to stand until the staindisappears, usually within 30 minutes,but it can be up to 24 hours.

3.  More than one application maybe required.

Mortar containing iron oxide colouringpigment will be lightened by this treatment.To maintain a uniform appearance treat anentire wall or keep the phosphoric acidclear of the mortar.

Protection should be provided topowder-coated fixtures, paintedsurfaces and concrete coloured withoxides, such as paths and roof tiles,to prevent discolouration by thephosphoric acid solution.

Oxalic acid

1.  Use a solution strength of 20 to 40 gramsper litre of water.

2.  The method of application is the sameas for the phosphoric acid treatment.

3.  More than one applicationmay be required.

4.  Neutralise the oxalic acid by applyinga solution of 15 grams of SodiumBicarbonate per litre of water. Donot wash off.

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Calcium stainsCalcium stains appear as almost a milky filmon the brickwork. These hard white depositsare invisible when wet but insoluble inwater, unlike efflorescence which iswater soluble.

Most commonly these stains arise fromproducts of the setting reactions of portlandcement and bricklaying sand containing

clay. The combination of clay from themortar with calcium and silica residuesfrom the cement, form calcium silicate thatproduces the insoluble white scum. Calciumsilicate is highly insoluble in most acids.

Kaolin, a clay mineral present in mostbricklaying sands, can also form a harddeposit. It is insoluble in most acids excepthydrofluoric acid.

Staining can occur in any of the

following ways:• Incorrect hydrochloric acid cleaning.

When too much acid and too little waterare used, the products of the reactionbetween the acid and the mortar areabsorbed into the brick faces instead ofbeing washed clear of the wall.

•  When newly laid masonry is unprotectedand saturated by rain, lime is put intosolution either from the cement or

hydrated lime in the mortar.•  By the interaction of lime leached by

water from concrete elements orcement rendering.

•  By the wet sponging of mortar joints thatsmears a cement-rich mortar film overthe brick face.

Typical calcium stain from wetsponging mortar joints

Calcium stains leaching from

adjacent concrete balcony

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Removal techniquesfor calcium stains

The application of Noskum or an equivalentproduct at full strength will usually removethese stains. In some cases, the reactionis immediate and should be followed byvigorous scrubbing. In others, the cleaningsolution should be allowed to stand forsome four to six minutes prior to scrubbing.

A small test area should be used todetermine the appropriate treatmenttechnique. More than one chemicalapplication may be required. The wallshould be rinsed thoroughly aftereach treatment.

Note: The manufacturer’s instructions andsafety precautions must be followed whena proprietary cleaning product such asNoskum or its equivalent is used.

Cleaning of Clay Masonry – Code of Practice /  15

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Vanadium stainsLight-coloured clays often containvanadium salt that are generally colourless,but under certain conditions may appearas a yellow, green or reddish-browndiscolouration of the brick.

It is essential that any vanadium saltsevident prior to the removal of mortarresidue be removed, as the hydrochloric acid

may turn the salt black and become difficultto remove.

Vanadium stains are often generatedby the use of too strong a concentrationof hydrochloric acid during the initialcleaning process, or from excessivewater penetration.

Vanadium stains are neither permanentnor harmful and do not indicate a defect inthe brick. Vanadium stains in exposed areas

generally wash off in time but their removalcan be hastened by chemical treatment.

After the initial removal of vanadium stains,more water on the masonry – even thatused in the cleaning process – may inducefurther efflorescing of the salts to thesurface, depending on the amountwithin the brick.

Vanadium as a green stain onlight coloured bricks

Vanadium stain not removed prior tohydrochloric acid application

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Removal techniquesfor vanadium stains

A number of chemical treatments areavailable to remove vanadium stains. It isbest to test the efficiency of these chemicalson a test area to determine the mostsuitable treatment to use.

Sodium hypochlorite

This is the active ingredient in household

bleach and swimming pool chlorine. It isan inexpensive treatment for mild cases ofvanadium staining. Simply spray or brushsodium hypochlorite onto the stain withoutpre-wetting, allow it to stand until the staindisappears, and then rinse.

Oxalic acid

This is probably the best known chemicalfor removal of vanadium stains. However if

used it must be followed by a neutralisingwash. This action is commonly omittedand further staining of a serious nature canresult. The correct procedure is:

1. Mix 20 to 40 grams oxalic acid per litreof water (preferably hot).

2.  Apply to the stained brickswithout pre-wetting.

3.  Neutralise the oxalic acid by applyinga solution of 15 grams of Sodium

Bicarbonate per litre of water.Do not wash off.

Potassium hydroxide or sodiumhydroxide (caustic soda)

Mix 150 grams potassium or sodiumhydroxide per litre of water and apply tothe stained bricks. Leave on the wall untilthe stain disappears, then wash off. A whiteresidue may appear after this treatmentand this should also be hosed off. Extracare should be taken when using highlycorrosive solutions such as these.

Proprietary cleaners

These are general purpose cleanersthat rapidly remove the stain. Themanufacturer’s instructions and safetyprecautions must be followed whenusing a proprietary cleaning product.

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EfflorescenceEfflorescence is not a stain, it is a powderyand sometimes ‘fluffy’ deposit thatforms on the surfaces of porous buildingmaterials such as masonry units, mortarand concrete. The temporary appearance ofefflorescence is common on new masonry.

The formation of efflorescence requiresthree conditions:

•  The presence of soluble salts.

•  Excessive amounts of water enteringthe masonry.

•  The evaporation of water as the masonrydries out, depositing salts on the surface.

The soluble salts that appear asefflorescence can enter the wallfrom various sources:

•  Mortar components, particularly cement.

•  Soil or fill in contact with the wall.

•  Sea spray in coastal areas.

•  Masonry units, however this is not acommon source.

Any situation that allows excessiveamounts of water to enter the wall islikely to promote efflorescence. Themost common causes are:

•  Poor copings and flashings.

•  The failure to protect new brickworkwhen rain interrupts bricklaying.

•  Poor storage of masonry units on site.Before units are placed in the wall theycan absorb ground salts and excessivewater in the stockpiled masonry, and canmobilise latent salts if they are presentin the masonry.

Persistent efflorescence may be a warning

that water is entering the wall throughfaulty copings, flashings or pipes.

Efflorescence as seen on brick faces

Effloresence from ground salts

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Removal techniquesfor efflorescence

Most efflorescence will naturally disappearover time, however its removal can beaccelerated by brushing with a stiff drybrush. The use of a dust pan or vacuumcleaner to collect the salts after brushingis recommended as this will prevent saltsfrom re-entering the brickwork or anyporous paving materials below.

After brushing and cleaning up, anabsorbent cloth (wrung out until damponly) can be used to pick up any residue.Frequent rinsing of the cloth in freshwater is advisable. Rinsing brickworkwith water will only cause the salt tobe reabsorbed into the bricks andreappear when dry.

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Graffiti and paintThese are difficult stains to remove,particularly if they have aged. Oldpaint deposits will probably require acombination of removal techniques.

Removal techniquesfor graffiti and paint

Fresh aerosol paintUse a commercial paint removerin accordance with themanufacturers’ instructions.

Oil-based paints or enamels

Burn off and follow with scraping andwire brushing ensuring not to damagethe brickwork.

Dried paint

1.  Flood the stained area for a few minuteswith a paint remover of the methylenedichloride type.

2.  Scrub to loosen the paint film.

3.  Flush with water to wash away theloosened paint.

4.  Scrub with scouring powder until thestain is removed.

Poultice methodIf these methods do not remove all tracesof the paint, it will probably be necessaryto apply a poultice:

1.  Mix a strong solution of sodiumhydroxide (caustic soda) in an inertbase such as diatomaceous earth.

2.  Apply to a depth of about 5 mm, andleave on the wall for at least 24 hours

before hosing off.

Iron and welding spatterWhere unprotected steel is built intomasonry, unsightly rust stains may resulton both bricks and joints. Similar stainswill occur if welding is carried on too closeto masonry.

Removal techniquesfor iron and welding spatter 

Phosphoric acid

1.  The application strength and durationwill vary. As a general guide, use amixture of 1 part phosphoric acidto 6 parts water.

2.  Apply by brush or spray to the dry walland allow to stand until the staindisappears, usually within 30 minutes,but can be up to 24 hours.

3.  More than one application maybe required.

Oxalic acid

1.  Use a solution strength of 20 to 40 gramsper litre of water.

2.  The method of application is the sameas for the phosphoric acid treatment.

3.  More than one application maybe required.

Proprietary cleaners

These are general purpose cleanersthat rapidly remove the stain. Themanufacturer’s instructions and safetyprecautions must be followed when usinga proprietary cleaning product.

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Oil, bitumenand tar stainsThese stains generally arise from the actionsof other trades or due to a lack of care inprotecting materials in the structure.

Removal techniquesfor oil, bitumen and tar stains

1.  Treatment with a commercialemulsifying agent (degreasing solution).

2.  Mix an emulsifier with kerosene to movethe stain. Clean the kerosene off with theemulsifier only mixed with water.

  Hardened oil must first be scraped offor free oil mopped up immediately withan absorbent, such as paper towels.Wiping should be avoided as it spreadsthe stain and tends to force the oil into

the masonry.

  The area affected should then be coveredwith a dry absorbent material such asdiatomaceous earth, hydrated lime, orwhiting and the procedure repeated untilthere is no further improvement.

  (The selection of the absorbent materialwill be a function of the colour of theunit and the acceptability or otherwiseof materials being trapped within

interstices in the surface.)

3.  Steam cleaning with a hot 10 percentsodium hydroxide solution may also beused but there is a risk of bleaching.

4.  A further method is to apply a poulticeof naphtha or trichloroethylene to thestained area.

Organic growthsThese are common where masonry is incontact with damp soil, such as flowerboxes, retaining walls and in sunless spots.

Some control of organic growth can beachieved by the use of water repellents orclear sealers. Flower boxes and the rearof brick retaining walls should be cementrendered with waterproof mortar or covered

with heavy duty plastic sheeting to preventwater seepage into the wall.

It is also advisable to render the top of thesewalls or provide a brick coping, ensuringthat a good cross fall is provided toshed water rapidly.

Removal techniquesfor organic growths

As much growth as possible should beremoved by vigorous brushing with a bristlebrush. For heavy growth, scraping and wirebrushing may be necessary.

After this dry cleaning, apply a proprietaryweed killer or liquid chlorine that should beleft on the surface for several days. Brush offand clean with hot water and detergent.

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Smoke stainsThese stains vary from minor conditionsaround domestic open fireplaces to majorproblems of cleaning of face masonry infire-damaged buildings.

The following chemical treatments may besupplemented by high-pressure water jetcleaning to scour the many small creviceson the masonry surface.

Removal techniquesfor smoke stains

Minor stains

Minor stains can be removed readily withsugar soap that is a highly alkaline mixture.Mix about 500 grams into 2 litres of hotwater and apply liberally by brush. After thestains disappear scrub with a mixture of

detergent and a household scouring powdercontaining sodium hypochlorite.

Noskum or equivalent products are alsoeffective in smoke stain removal.

Smoke-damaged buildings

The problems in fire-damaged buildings areusually complex, with widespread smokestains and localised severe staining wherehighly-combustible materials have burnt.

An initial treatment with sugar soap willremove some of the deposits. This canbe followed by an application of sodiumhypochlorite. The full strength chemicalshould be left on the wall for about 10minutes before scrubbing and hosing.

General cleaning with Noskum or anequivalent product after these applicationsmay complete the cleaning.

Note: The manufacturer’s instructions andsafety precautions must be followed whena proprietary cleaning product such asNoskum or its equivalent is used.

Severely-affected areas

These may require a poultice treatment:

1.  Use an inert filler material such asdiatomaceous earth, mixed withsodium hypochlorite (bleach) to forma thick paste.

2.  Apply to the stained areas by trowel orsteel float to a depth of 5 mm.

3.  Leave on the wall 24 to 48 hours beforeremoval by hosing and scrubbing.

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Soil and grimeBase courses of masonry are frequentlydisfigured with splashing from adjacentsoil. These deposits should be removed assoon as possible.

These stains arise from long-term airbornedeposition. Grime is worst in industrialareas with heavy pollution problems.Special cases can arise, for example from

bird fouling or proximity to railway lines.Horizontal surfaces such as ledges, sillsand raked masonry joints are the worstaffected areas.

Removal techniquesfor soil and grime

Scrubbing with a fibre or soft bronze bristlebrush and a liquid detergent is usually

effective. Steel wire brushes should notbe used, to avoid rust staining frombroken bristles.

Large jobs are usually carried out byspecialist cleaners using high-pressurewater and dry or wet sandblasting. Testcleaning should be carried out before thefinal cleaning technique is adopted.

Timber stainsThese usually arise from waterspreading tannin or resin stains on thewall, particularly from hardwoods. Thestains are usually brown or grey and arepresent on both bricks and mortar.

Removal techniquesfor timber stains

Normally timber stains will be removed byscrubbing with a solution of 20-40 gramsoxalic acid per litre of hot water. Neutralisethe wall after this treatment.

Where the stain is not removed by thissolution, two other treatments can beused. One is to apply a bleaching solutioncontaining sodium hypochlorite and allowit to dry on the wall. The other treatmentis the same as that recommended for theremoval of acid burn given in this section.

Noskum or equivalent products have alsobeen found to be effective in removingthese stains.

Note: The manufacturer’s instructions andsafety precautions must be followed whena proprietary cleaning product such asNoskum or its equivalent.

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Manganese stainsA dark-blue brown discolouration mayoccur on bricks that have been colouredgrey or brown by the addition of manganeseduring manufacture. The stain occurs mostcharacteristically along the edges of thebrick and is generally caused by excessivewater penetration. In severe cases it mayshow as a stain across the face of the brick.

The problem with manganese staining isnot so much the removal of the stain, aspreventing its return in a short period by:

•  Minimising water penetration intobrickwork by ensuring all mortar jointsare filled.

•  Using ironed joints as they form a betterweather-shield than other types.

•  Ensuring copings at the top of the wallare effective.

•  Covering all brickwork under constructionduring periods of wet weather.

•  Insertion of effective damp proofmembranes as brickwork progresses.

Signs of manganese staining

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Removal techniquesfor manganese stains

Phosphoric acid

1.  Mix 1 part phosphoric acid to6 parts water.

2.  Apply with brush or spray to dry wall.

3.  Avoid splashing any adjoiningmetal surfaces.

4.  Reaction can take up to 24 hoursand more than one application maybe required.

Acetic acid

1.  Mix 1 part acetic acid (80% stronger)with 1 part hydrogen peroxide (30 to35% concentration) with 6 parts water.

2.  Apply with brush or spray to dry wall.

3.  Avoid splashing any adjoining

metal surfaces.

4.  Reaction should be almost immediatehowever more than one applicationmay be required.

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PO Box 751, Willoughby NSW 2068 Australia

Technical enquiries 1300 667 617


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