Basic Block Laying

Tutor Copy

Types of building blocksThe face side of a block usually measures

440mm x 215mm

The thickness can vary from 75mm up to 300mm

The weight from 9.9kg to more than 30kg.

75mm – 300mm

215m

m440mm

Blocks are manufactured to meet compressive strength

standards of between 2.8N/mm² and 7N/mm².

Blocks can be solid, hollow or cellular.

Some blocks have insulating material bonded to one

face or inserted in the voids

Blocks are available in a range of densities.

Blocks that are light in weight are usually less dense

because they are made from an aerated mix.

The heavier blocks are denser.

Aerated block

Load bearing blocksThese blocks are usually made of Portland cement

and a variety of aggregates. The blocks are precast in

moulds and compacted with the aid of vibration, or in

a moulding machine involving the use of compressed

air, or a combination of both.

Block making machine

Non-load bearing blocksThese blocks are usually made of Portland cement and a

variety of lightweight aggregates; therefore they are not as

dense or as strong as load-bearing blocks.

These blocks are pre-cast in moulds or they can be

produced in slab form and cut to size when set.

Two well known manufacturers are Thermalite and Celcon.Aerated block making

Lightweight BlocksThese blocks are made from lightweight or low

density materials such as fuel-ash, clinker, or

lightweight aggregates bonded together with cement.

They are easy to lift and handle and have good

thermal and sound properties

They can absorb water and are be easily broken

during handling and construction.

Lightweight blocks can be cut with a bolster chisel / hammer,

a hand saw or power saw.

It is good working practice to secure blocks when cutting

with hand or powered tools.

Alternative methods of bonding a

return quoin.

Special blocksMany manufacturers provide special blocks that assist in the

bonding and prevent wastage.

These blocks range from coursing blocks to half, quarter and three-

quarter blocks. Other special blocks include return and reveal blocks

which are used to close the cavity at door and window openings.

Special / Coursing BlocksTo maintain bond within a wall it may be necessary to use

either coursing bricks or blocks. These can be cut from a

whole block or special blocks manufactured to those sizes.

These blocks are built into the

walling at junctions and over

openings in the wall. Ordinary

facing or common bricks

should NEVER be used for this

purpose.

Plug and screw

This is a common type of fixing specially designed for fixing

to all blocks. It consists of a plastic plug which is driven into

a pre-drilled hole. A screw can then be driven into the

hollow centre of the fixing.

Fixings and finishes

Blockwork below ground level

Trench Blocks

These blocks are bigger in size than normal blocks with a face

dimension size of 440mm x 215mm and are available

in a range of thicknesses ranging from 255mm to 355mm.

One trench block is equivalent in size to 2 aggregate blocks,

or 12 bricks, plus wall ties and infill.

Blockwork below ground levelThe following typical details illustrate the proper use

of blocks below DPC level.

Render Coating

Painted wallDPC

Trench block

Plaster

Ground floor

Foundation

Typical solid foundation in

blockwork

Blocks used below ground level

Blocks are available in a weight less than 20kg with handholds and will comply with CDM Regulations which cover health and safety issues on site for repetitive handling.

Solid Blockwork Foundation with an Insulated Cavity Wall

This form of construction incorporates a blockwork

foundation below ground level with a traditional brick and

block cavity wall above. The cavity can be partially filled or

full filled as required.

This type of construction offers a structure with good sound

and thermal insulation qualities.

Solid Blockwork foundation with an insulated cavity wall

Facing Brickwork

DPC

Plaster

Partial fill cavity insulation

Ground floor

Foundation

Trench Blockwork

Block cavity wall foundation

This is an alternative solid block foundation construction. The blocks below ground level are laid to form a cavity which is then filled up to ground level with a cement / aggregate mix. The cavity can be partially filled or fully filled as required.

Block cavity wall foundation

Facing Brickwork

DPC

Plaster

Partial fill cavity insulation

Ground floor

Foundation

Cavity blockwork

Cement aggregate mix

Apart from the size of the blocks the building operations

used to erect walls are the same as for brickwork.

There are 10 blocks per square metre as opposed to 60

bricks per square metre

Never mix different types of blocks in the same run of walling,

and do not use common or facing bricks as closers as they

will reduce the thermal and sound insulation qualities of the

blockwork.

Always set out the first course dry so that the position of cut blocks can be found.

Any adjustment to the width of joints should be made to achieve and maintain a

bond within the wall.

This is called “Dry Bonding”

Blocks should be laid to a regular bond, usually half bond where possible.

Never lay blocks to a bond of less than quarter bond.

It is not always convenient to build a

junction wall at the same time as the

main wall.

Tee junctions are normally bonded, or

ties can be use with a straight joint.

Indents may be left to allow bonding to

occur at a later stage. Indents are gaps

where blocks will be inserted at a later

date.

Wall ties

Bonded

Junctions to walls

Junctions to wallsThe diagram shows a typical method of constructing

junction walls.

Brick outer leaf Inner leaf walls 100mm

Separating wall 100mmNominal 8mm internal render scratch finish

Partial fill cavity wall 12.5mm gypsum board

mounted on dabs

Tied junction

100mm partition

75mm / 275mm min

Bonding should be set out so that lintels bear preferably

on a whole block. If this is not possible, a minimum two-

thirds length block is acceptable but definitely not less.

(normally by at least 150mm.)

Some types of hollow and cellular blocks may need to be

filled under lintel ends to provide sufficient bearing

strength.

In windy weather, block walls should be restrained by

temporary propping.

In windy weather, the day work lift height may be reduced

as an alternative to propping.

Blocks should be kept dry before use.

Use only specified mortar mixes and ensure that bed and cross

joints are solidly filled.

Maintain gauge to correspond with brickwork gauge.

Building with blocks is quick and the weight of the blocks could

cause fresh soft mortar bed to be squeezed out. This could

result in collapse / loss of gauge / loss of plumb.

Internal Blockwork External Brickwork

Cavity insulation and wall

ties

Typical cavity wall construction using facing bricks and blocks

Closing cavities of external walling built with blocks

With all cavity walls it is essential that the cavity be closed at

reveals, such as door and window openings. This can be

achieved by using cut blocks or by using special reveal blocks

manufactured for the purpose.

Cavity wall closersAnother way of sealing the cavity at openings is to use

ready made cavity closers. These are usually made from

tough plastic and internally insulated to prevent cold

bridging. They also have provision for fixing clips to be

attached and built in as the brick / block work proceeds.

For bonding purposes, three courses of brickwork are equal

to one course of blockwork.

This makes bonding simple as long as both bricks and blocks

are kept accurately gauged.

Plaster or smooth faced finish

Solid internal wall

Cavity partition wall

Internal plasterSmooth faced blockwork