Arba Minch University Civil Engineering Department
Chapter IV
Bricks
2.1 Introduction
Building bricks may be defined as “structural units of rectangular shape and convenient size that are
made from suitable types of clays by mounding, drying and burning.”
It is now established that even in remotely ancient civilizations bricks were the common material for the
construction. Even at present, brick is the most basic and favoured material for common construction
throughout the world. This may be attributed to a number of advantages it offers over other available materials
of construction like stones and concrete.
These may be summarized as follows:
Availability: since clays are available almost universally, bricks can be made out of them in every region.
This is not true either for stone or for concrete.
Construction Methods: this is not so stones, where experienced hands are less easily available. With
concrete, only a very experienced and qualified person can handle the construction work.
Size, shape and handling: Bricks are made in “ready to use” sizes and shapes which are very convenient
to handle and use. For stones, a good deal of dressing is absolutely essential. In the case of concrete, an
elaborate form-work and shuttering are basic requirements, and its transport and lying requires great care
and caution.
Cost: because of the factors mentioned above, brickwork is cheaper compared to the two types of
constructions. Where bricks are not available locally, and have to be transported from far off distances, and
locally available stone may give a cheaper construction.
2.2 MANUFACTURE OF BRICKS
The process of manufacture of bricks is carried out in a number of stages. These are listed below. Each stage
has its own specific importance
Selection of suitable type of brick earth.
Preparation and Tempering of Mud.
Shaping or Molding of brick units
Drying of molded bricks
Firing or burning of units
Cooling of the units
2.3 Properties of Bricks
The essential properties of bricks may be conveniently discussed under four headings: physical
properties, mechanical characteristics, thermal characteristics and durability.
Lecture Note Instructor: Getasew M. Page 1 of 4
Arba Minch University Civil Engineering Department
2.3.1 Physical properties
These include shape, size, colour and density of a brick.
Shape: The standard shape of an ideal brick is truly rectangular. It has well defined and sharp edges. The
surface of the bricks is rectangular and even. For special purpose bricks may, however, be either cut or
manufactured in various other shapes.
Size: The size of the brick used in construction various from country to country and from place to place in
the same country.
Country Length Thickness Height
(cm) (cm) (cm)
United Kingdom 20 9.5 5.5
United States of America 20 10 10
(USA) 30 10 10
U.S.S.R 25 12 6.5
Ethiopia 25 12 6
Colour: The most common colour of building bricks falls under class RED.
Density: In the case of standard bricks, density various from 1600 to 1900 kg/cubic meter
2.3.2 Mechanical characteristics
Under this comprehensive strength and flexure strength are included.
Comprehensive strength: the comprehensive strength of a brick depends on the composition of the clay
and the degree of burning.
Flexure strength: they should possess sufficient strength against transverse loads. It is specified that the
flexural strength of a common building brick shall not be less than 1Mpa. Best grade bricks often possess
flexural strength over 2 Mpa
2.3.3 Insulation
Besides being hard and strong, an ideal bricks should also provide adequate insulation against heat,
cold and noise.
The heat and sound conductivity of bricks varies greatly with their density and porosity. Very dense and heavy
bricks conduct heat and sound at a greater rate. They have, therefore, poor thermal and sound insulation
qualities. For this reason, bricks should be so designed that they are light and strong and give adequate
insulation.
2.3.4 Durability
By durability of bricks is understood the length of time for which they remain unaltered and strong when used
in construction.
The durability of bricks depends on a number of factors such as: absorption value, frost resistance and
efflorescence.
Lecture Note Instructor: Getasew M. Page 2 of 4
Arba Minch University Civil Engineering Department
2.4 qualities of a good brick
It should have a rectangular shape, regular surfaces and red colored appearance.
It should confirm in size to the specified dimensions.
It should be properly burnt. This can be ascertained by holding two bricks freely, one in each
hand, and striking them. A sharp metallic sound indicates good burning whereas a dull thud
would indicate incomplete burning.
A good building brick should not absorb water more than 20 % of dry weight. Absorption not
more than 25% in any case.
A good building brick should possess requisite comprehensive strength, which in no case
should be less than 3.5 Mpa. A rough test for the strength of the brick is to let it fall freely from a
height of about one meter on to a hard floor. It should not break.
Bricks should be hard enough so that it is not scratched by finger nail.
A good brick has a uniform color and structure through its body. This can be checked by taking
a brick from the lot and breaking into two parts. The broken surface in both the half same
appearance and structure.
2.5 Types of Bricks
2.5.1 Types Based on Modification in Shape
In construction, there are positions where a perfect rectangular shape will not be suitable. It has to be
modified. Such bricks are required in the plinth, the corners of the walls and at the copings.
2.5.2 Types Based on perforations or cavities
Three types of bricks: perforated bricks, hollow bricks and channeled bricks.
2.5.2.1 Perforated Bricks
In perforated bricks, cylindrical, rounded or rectangular holes are made in the bricks after the moulding stage,
these holes are called perforations. They are properly spaced from the side of the brick; minimum distance
being 15 mm. further distances between any two perforations is not less than 10mm. the volume of the
perforation may be as much as 20 – 50% of the total volume of the brick.
The perforated brick may be larger in size than ordinary building brick which is a distinct advantage in that work
output of masonry will increase considerably with the use of perforated bricks.
The major advantage that perforated bricks offer over ordinary bricks is:
i. These bricks are light in weight
ii. Less quantity of clay is required for their manufacture
iii. Less time is required for drying and burning of perforated bricks
iv. These offer better resistance against rain penetration and better insulation against heat. As
such they are ideally suited for tropical countries
v. Efflorescence is least in perforated bricks
vi. These are especially suitable for construction of brick panels in multistory structures.
2.5.2.2 Hollow Bricks
A brick also called cavity brick or cellular brick has a few well defined sets of cavities with specified
dimensions made in the body of the brick. As a result, its net weight may be only one-third to one-half of the
solid brick. It is important that the thickness of brick wall near the cavity should not be less than 2cm.
They offer following advantages over the ordinary solid bricks
i. Being light in weight, they can be handled more conveniently and the output of the mason may be three
to four times compared with ordinary bricks.
ii. They offer better insulation against heat and sound.
iii. They are ideal and economical for non-load-bearing walls, e.g. partition walls
2.5.2.3 Channel or Gutter Brick
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Arba Minch University Civil Engineering Department
They are actually special purpose bricks having a continuous central semi-circular cavity or depression
running through their length. Very often they are glazed to make them impervious. These find use in the laying
of drains.
Lecture Note Instructor: Getasew M. Page 4 of 4
