4 Bricks classes|Classifications,testing

Bricks wall

Bricks are the building material, obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning these blocks.

4 bricks classes classifications

Bricks wall
Bricks wall
The bricks  divided into two categories as given below:
1. Un-burnt or Sunburnt

Un-burnt or Sunburnt

The un-burn or sun-dried are dried with the help of heat received from the sun after the moulding process.
They can only be used in the construction of temporary and cheap buildings


Burnt ones are used in construction works and they classified into 4 classes.
  1. First-class
  2. Second class
  3. Third class
  4. Fourth class.


These first-class ones are of standard size and are table-moulded & burnt in kilns.
The colour of burnt bricks will be in deep red, cherry or copper colour.
The surface of the brick will be smooth with sharp and straight edges at corners.

Given below quality observations for first-class

1. First-class ones should be free from flaws, cracks and stones.
2.No impression should be on the done when a scratch is made by the fingernail.
3. There should not show any lumps on the fractured exterior of the brick
4. Water absorption should be 12 to 15% of its dry weight when immersed in cold water for 24 hours.
5. Crushing strength of first-class should not be smaller than 10.5 N/sq mm.
6. A ringing or metallic sound should occur when two blocks are stuck facing each other.

Uses of first-class

1.Pointing of block masonry
3.Exposed face work in a masonry structure
4.Reinforced brickwork.

2.Second class

These second class bricks are moulded on the ground and they are burnt in kilns.

Given below quality observations for second class

1. In Second class bricks, Small cracks and distortions allowed.
2.No impression should be on the bricks when a scratch-made by a fingernail.
3. Water absorption should be 16 to 30% of its dry weight when immersed in cold water for 24 hours.
4. Should not show any lumps on the fractured exterior of the brick.
5. A ringing or metallic sound should come when two blocks are stuck facing each other.
6. Crushing strength should not be smaller than 7 N/sq mm.


1. In all unimportant and important masonry works this type is utilised.

3.Third class

They are heated in clamps and these class ones are ground -moulded.
They are soft,un-burnt and of light colour giving dull sound.
 Approximately 25% of dry weight is Water absorption.


Used for building temporary structures.

4.Fourth class

These fourth class ones are burnt over and distorted badly in size, shape and they are brittle.


This fourth class bricks ballast is used in lime concrete floors, foundation and metal roads.


They are of uniform size & are of lightweight, they can be properly arranged and no lifting appliance is required.
Clay bricks are used in construction and they made of sand and lime.

Standard Size:

Standard size of  brick  =19cm x 9cm x 9cm (with our mortar)
Standard size of  brick =20cm x 10cm x 10cm (with mortar)
standard size of brick use at construction site
                                      =23cmx11.5cmx7.62cm or 9”x4.5”x3” size (with out mortar).
An indent of 1 to 2 mm deep formed on the top is called a frog.
The purpose of providing a frog is to form a key for holding mortar.

Composition of good brick earth:

The following are the good brick earth ingredients

a. Silica-50% to 60%
b.Alumina- 20% to 30%
c.Lime: <10% (5% desirable)
d.Magnesia: <1%
e.Ferric oxide :<7%
f.Alkalies :<10%

Functions of the various ingredient’s

a. Silica

Silica enables the brick to keep its shape and imparts durability.
Excess silica makes the brick brittle and weak on burning.


Alumina imparts plasticity to the earth so that it can be moulded.
Excess quantity produces cracks in brick on drying.


Lime prevents shrinkage of raw brick.
Excess lime causes the brick to melt and loses its shape.
Presence of excess lime in lumps absorb moisture, swells and causes disintegration of brick.

d. Oxides of Iron

It imparts red colour to the brick.
It improves impermeability and durability.
Presence of Iron pyrites makes the brick crystallized and disintegrate during burning.

e. Magnesia

Imparts yellowish tint and decreases shrinkage.
Excess of magnesia results in the decay of brick.
Harmful ingredients in brick earth

F. Alkalies

They are mainly in this form of Soda and Potash.
Excessive alkalies make the clay unsuitable.
Causes efflorescence i.e white powder deposits on a brick which spoil the appearance.


Presence of pebbles in brick earth will result in the week and porous brick.
The brick containing pebbles will not break as desired.

Vegetation and organic matter

The occupancy of organic matter and vegetation present in brick earth assists in burning.
They increase water absorption, make the brick porous and it decreases its strength.

Manufacturer of bricks :

1.Preparation of clay

The clay is made in the following order.
 Un-soiling of earth, Digging of earth, cleaning of clay, clay Weathering , Blending of clay and Tempering
i. Un-soiling 
The soil present in the top layer at a depth of 200mm is extracted and thrown away.


From the ground, the clay is then dug out and it is spread on the levelled ground surface.


 Cleaning is done to remove pebbles, stones and vegetable matter etc if any.


The clay is then exposed to an atmosphere for softening or mellowing.

v. Blending

Some ingredients are added by loosening the clay. This is termed as blending of clay.


Water is added to the clay in the required quantity and the whole mass is pressed or kneaded under the feet of cattle or man.
To obtain a homogeneous mass of clay of consistent character itis performed.
In the plug mill Tempering can also be performed.

2. Moulding

Moulding is the process of giving the required shape to brick from the prepared brick earth.
The following are the two ways of moulding:
1.Hand moulding
a. Ground moulding
b. Table moulding
2. Machine moulding


bricks drying
bricks drying
The drying is done to eliminate the moisture and to restrain the shrinkage, time, fuel during burning.
Within 3 to 4 days approximately 3%  of moisture content is brought down when it is kept underexposed conditions


bricks yard
bricks yard
 In this manufacture burning is a very critical operation.
This burning is achieved in a kiln or clamp.
It imparts strength and hardness to the brick and makes them durable and dense.

Strength of brick :

The following factors affect its strength

  • Composition of brick earth
  • Preparation of clay and blending of ingredients
  • Nature of moulding adopted
  • Care was taken in drying and stacking of raw or green bricks.
  • Type of kiln used including type of fuel and it’s feeding.
  • Burning and cooling process
  • Care to be taken during unloading.
The average crushing and tensile strength of hand moulded are 60000 KN/m2 and 2000 KN/m2 respectively.

Testing of brick as per IS:3495-1966 :

The following test preferred for testing:

1.Water absorption test.
2.Compression strength  test
3. Efflorescence test
4.Warping test

1.Water absorption test.

a. 24 hours immersion cold water test

The strength of brick also depends upon its water absorption capacity.
It the brick have more absorption capacity, it will lose its strength earlier.
The specimens must be cooled to room temperature and weighed. Let it be W1 units.
The dry and cooled specimens shall be completely immersed in clean water at 27 (+/-) 2 for 24 hours.
By removing each specimen the surface water is cleared off with a damp cloth and then weighed.
Within three minutes weighing should be completed  after separating the specimen from water
Let the weight be W2 units
The water absorption capacity of the specimen is obtained using
weight of the specimen =W1
After soaking in water obtained weight =W2
% of Water absorption =100 x ((W2-W1)/W1 )

b.Five hours soiling water test

The brick specimens are immersed in water and boiled for five hours and the water absorption is obtained as % by weight of bricks.

2. Compressive strength test

This test is performed to know the crushing strength which should not be less than the specified limit.
With horizontal flat faces, the specimen is arranged in the compression testing machine for testing.
At a speed of 14 N/mm2 per minute, the load applied till collapse.
The compression strength is calculated by dividing the maximum load at the failure by the area of brick.

3. Efflorescence test

This test is done to know the presence of alkaline matter in the brick.
They are kept in a 150mm dia glass dish containing 25mm depth of water at room temperature.
On the brick exterior, white or grey patches appear on drying.

Presence of efflorescence is classified as:

a. Nil

When no visual deposit of efflorescence


When the brick surface is covered with a thin deposit of salts not more than 10% of area, then it is termed as slight efflorescence.


If the exposed area of brick is deposited salts between 10% to 15% of surface area, then it termed as the moderate Efflorescence.


Deposits are heavy and I the flakes or powder falling from the surface of the brick with heavy deposits of salts, then it is termed as serious Efflorescence.


Efflorescence is greater than 50% of the exposed area of brick.

4. Warping test

Using a glass-surface or flat stool warping test is performed and measure the largest distance between the straightness edges of the brick surface.
This test is of two types:
a.Concave warpage
b.Convex warpage

Refractory bricks :

Without becoming soft or melting, the clay which can tolerate high temperature is termed as
refractory or fire clay.
This clay is burnt at a very temperature in a special kiln.
Fire clay has grater % of alumina.
These clays are capable of resisting of high temperature up to 1700 degree Celsius without softening.
Presence of a small percentage of lime and magnesia help to melt the clay particles at high temperature.


Refractory brick is used in lining furnaces having acid slag, steel industries, coke oven and copper reverberatory furnaces.

Additives in the manufacture of Brick

The following are the additives used:

1.Fly ash
2.Sandy loam
3.Rice husk
4.Basalt stone dust.

1.Fly ash

 From thermal power plants, this Fly ash waste material is available.
This includes mullite, amorphous glassy material, magnetite, hematite etc.
In clay bodies, these silicates help to improve strength on firing.
By adding Fly ash chock drying losses and shrinkage on drying can be reduced.

2.Sandy loam

Sandy loam is effective in controlling the drying behaviour of highly plastic soil which contain an expanding group of clay.

3.Rice husk ash

Carbon content should be <3 % to 5 %
In plastic soils which shows excessive shrinkage’s this rice husk ash is utilised.

4.Basalt stone dust

 From blast stone crushing units basal stone dust is available as the waste product in extensive quantity.
This is utilised to improve the drying, shaping and firing performance of bricks.

How many bricks required for 3.7 m3 brickwork, size of brickwork 190mm x 90mm x 90mm?

Answer: Volume of one brick = 0.19m x 0.09m x 0.09m = 0.01539 Cum
For 1 m3 No. of bricks required =1/0.01539
                                    = 649.77,  approximately 650 bricks are required.
So, for 3.7 m3 Numbers required  = 3.7 x 650 =2405.
So, for 3.7 m3 brickwork, approximately 2405 numbers are required.
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About Ashwini Kumar

Ashwini Kumar is a graduate in civil engineering from NIT Warangal. He has 8+ years of experience in the construction field. He is the author, founder of the Easy Home Builds blog

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