3. Types of building blocks
The 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
215mm
440mm
4. 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
5. 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
6. Load bearing blocks
These 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
7. Non-load bearing blocks
These 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
8. Lightweight Blocks
These 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.
9. 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.
12. Special blocks
Many 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.
13. Special / Coursing Blocks
To 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.
14. Delivery and storage
Blocks are delivered on site as banded packs or on
pallets.
The blocks must be stacked on a hard level base, or on
battens on drained even ground.
Loose blocks should be stacked
as they are used, i.e. on edge,
and the height of the stack
should be limited to two metres.
15. Delivery and storage
Blocks may be delivered with or without a shrink-wrap
covering, but all blocks should be covered from the elements
until required for use.
The packs should be placed on pallets if possible for ease of
handling and delivery around the site by a forklift truck.
17. Different finishes to Blockwork.
• Rendering
• External cladding
• Plaster dab method
• Timber batten method
• Metal firring systems
18. 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
19. 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.
20. Blockwork below ground level
The following typical details illustrate the proper use
of blocks below DPC level.
Render Coating
Painted wall
DPC
Trench block
Plaster
Ground floor
Foundation
Typical solid
foundation in
blockwork
21. 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.
22. 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.
23. Solid Blockwork foundation with
an insulated cavity wall
Facing
Brickwork
DPC
Plaster
Partial fill cavity insulation
Ground floor
Foundation
Trench Blockwork
24. 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.
25. Block cavity wall foundation
Facing
Brickwork
DPC
Plaster
Partial fill cavity insulation
Ground floor
Foundation
Cavity blockwork
Cement aggregate
mix
26. 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
27. 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.
28. 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.
29. 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
30. Junctions to walls
The diagram shows a typical method of constructing
junction walls.
Brick outer leaf Inner leaf walls 100mm
Separating wall 100mm
Nominal 8mm internal render scratch finish
Partial fill
cavity wall 12.5mm gypsum board
mounted on dabs
Tied junction
100mm partition
75mm / 275mm min
31. 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.)
32. 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.
33. 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.
34. Internal Blockwork External Brickwork
Cavity
insulation
and wall
ties
Typical cavity wall construction
using facing bricks and blocks
35. 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.
36. Cavity wall closers
Another 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.
37. 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.
