CHAPTER 2: BRICKS
º A brick is defined in BS 3921 as a walling unit with
coordinating or format size of 225mm(L) x 112.5mm(W) x
75mm(H) including 10mm mortar joint.
º Actual dimension is 215mm x 102.5mm x 65mm
Factors that affecting the selection of bricks
º Size flexible for any type of construction
º Colour and texture - natural
º Shape ability to form different type of bonding
º Bricks may be classified by one or more of the following:
ü Varieties common- suitable for gen. work but
- Facing specially made or selected to have
an attractive appearance when used
without rendering or plaster.
- Engineering dense and strong semi-
vitreous apart from uniform and standard
size and texture.
ü Qualities internal, ordinary (durable externally),
special (conditions of extreme exposure)
ü Types solid, perforated (small holes exc. 25%
vol.), hollow (larger holes exc. 25%),
cellular (holes closed one end, exc. 20%)
ü Place of origin
ü Raw material clay, calcium silicate, concrete
ü Manufacture wire cut, pressed, soft mud process
ü Use foundation
ü Colour blue
ü Surface texture sand faced
References: Chudley, R (2005) Construction Technology 4th edition
º Made from surface or deep mined clays that have necessary
plasticity and tensile strength.
º BS 3291: 1985
º Contain silica and alumina with metallic oxides (iron oxide-
causing red colour), calcium carbonate (causing yellow after
burning), and feldspar.
º 3 categories common, facing, engineering. (Differentiate)
º Properties of clay bricks:
ü Compressive strength min. 5N/mm2
ü Durability the ability to resist damage
- Resulted from fusion of clays during
burning (higher temp, more durable)
ü Water absorption affected by the manufacturing
process and the burning temp
- gen. 0.02% of the weight ( low)
ü Efflorescence soluble salts (magnesium & sodium
sulphate) lose water and crystallise
MANUFACTURING CLAY BRICKS
- requires 6 steps
i. Winning & storage
Winning is the term used to describe the mining of the clay. Most
bricks are made from surface mined clays dug from open pits. The
clays are moved by truck or rail to the plant where they are crushed
and moved to storage piles.
ii. Processing the raw materials
Clays are removed from the various storage piles and bended to
produce the desired chemical composition and physical properties.
The blended clays are then moved to crushers where stones are
removed and the clay lumps are reduced to a max. of about 50mm
in diameter. This material is then moved by conveyor to grinders to
be ground to a fine powder and passed over vibrating screens. The
fine material is placed in storage.
iii. Forming the bricks
There are 3 major methods depend on the properties of clay;
machine pressed, wire cut and soft-mud process (sand-struck/water
The moisture content of green bricks (unfired, newly formed
bricks) varies depending on the clay and the process used. Once
formed, the bricks are placed in a low temperature drier kiln or
leave them in open air for 1 to 2 days.
v. Burning and cooling
Involves raising the temperature of the dried bricks to a
predetermined level. There are 2 two types of kilns in use, periodic
kiln and a tunnel kiln. The higher the burning temperature the more
shrinkage and the darker the colour of the brick. The burning
process takes 24 to 150 hours. After that the cooling period begins
for 48 to 72 hours.
vi. Drawing and storage
After the cooling stage is complete, the bricks are removed from
the kiln, sorted graded and moved to storage. Often they are
stacked on wood pallets for loading by a forklift. Each pallet is
wrapped in plastic to keep the bricks dry.
Reference: Richard T Kreh, Masonry Skills, 3rd edition
CALCIUM SILICATE BRICKS
º Also called sandlime bricks (BS 187).
º Standard size as clay bricks.
º Made from selected clean sand or crushed flint (hard grey stone)
mixed with lime and water. Colouring pigment can be added.
º The relatively dry mix is then fed into presses to form the
º Then hardened in sealed and steam-pressurised autoclaves.
º Takes 7 to 10 hours to causes reaction between sand and lime.
º Resulting in a strong homogeneous brick ready for delivery.
º Very accurate in size and shape but do not have individual
characteristics of clay bricks.
3. High compressive strength
4. Exceptional heat resistance
5. Good sound insulation
1. 215 x 102 x 65mm
2. 215 x 102 140mm
3. 240 x 115 x 71mm
4. 240 x 115 x 115mm
Reference: Richard T. Kreh, Sr, (1990) Masonry Skills 3rd Ed. Delmar Publisher Inc, pg.11.