Bricks: Types of Bricks, Qualities, Required Test of Bricks

Bricks Types, Qualities, Required Test

Brick is most generally used building material and used for constructing walls, floors, and so on. It is a durable product that has high compressive strength making it ideal for use in the construction of buildings as a structural element. The word brick is referred to a rectangular product made of clay, concrete, lime, fly ash, etc.

Types of Bricks

There are many ways in which brick can be classified. Firstly bricks are defined by the manufacturing procedure.

Burnt Clay Block

The most popular types of bricks used in construction are clay bricks. These are generally referred to as common brick.
Burnt clay brick is molded from clay and then mostly dried in the sunlight and fired in a kiln. These types of bricks are further categorized by first class, second class, third class, and over burnt clay brick, which relate not just to look but also strength.

First-class Brick

They are more durable and have more strength. These bricks are well burnt, have a uniform color, water absorption of less than 15%, and minimum compressive strength of 10.5 N/mm2. They have a plane, rectangular faces with equal sides, and right-angled edges.


 Second class Brick

These bricks are rough and the shape is slightly irregular surface with water absorption below 20 % and minimum compressive strength of 7 N/mm2.

Third class Brick

They are not uniform in shape and are slightly under burnt should not have water absorption of more than 25%. Mostly used for temporary structures.

Over burnt bricks

They are over-burnt, irregular in shape, tough, and strong. These bricks are used in foundation, road material, and flooring.

Unburnt Bricks

Unburnt bricks are less durable. These bricks are used for temporary structures. Unburnt bricks are prepared by molding clay and after that dried in sunlight. They are not strong and also they have less water and less fire resistance. These bricks are not ideal for rainy areas.

Fly Ash Brick

Fly ash brick, also called fly ash clay brick is made from a combination of fly ash and clay fired at very high temperatures. The mix of fly ash produces brick that has higher levels of calcium oxide. They are less permeable so, they have lower amounts of water penetration, and also they are self-cementing. They also have higher density, endure freeze-thaw cycles better than clay brick. They have high fire insulation and high strength qualities.

Fire Brick

Fire brick is also called refractory brick. It is a type of brick that is built from fire clay. Fire clay has a very high melting temperature level of more than 1500 degrees Celsius as a result of its high alumina material. These bricks are designed to have high-temperature resistance, low thermal conductivity.

Fire bricks are mainly used in kilns, fireplaces, and various other similar places where there is directly facing to high-temperature conditions.

Concrete Bricks

Concrete bricks are made by a blend of Portland cement, water, and aggregate.

Concrete bricks are made by concrete into a mold to cast a properly sized brick product. The mold can be designed as per the required size and design. It can be made on architectural and aesthetic requirements. The finishes might be smooth or may look like natural stone. Different colors as pigments can be added to the concrete during the manufacturing of the brick. Concrete bricks are used for the construction of masonry and frame structure buildings, boundary walls.

If compared with clay bricks, clay bricks have much more compressive strength than concrete bricks. Concrete bricks are also more absorbent than clay bricks.

Sand Lime Brick

Sand lime bricks are also called calcium silicate bricks. It is constructed from a mixer made up of sand, lime, and water. A pigment is often added to the mix to obtain different colors for the brick. The color is mostly grey. It is used as a load-bearing member as it is very strong in compressive strength.

Engineering Brick

These bricks are recognized for many factors. They have high compressive strength and low absorption capacity. They are extremely strong and dense. They have a good bearing capacity and have a smooth red shade.

They are categorized into many Classes like A class, B Class, C Class. A class is the best however Class B is most utilized. They are used for most civil engineering projects like sewers, manholes and etc.

Qualities of Good Brick

Some basic things should be considered before utilizing the bricks and also check the quality of bricks hence they are most important for structure. Some of the features are mentioned below:

  • Brick soil should be free from stones, any organic component, and free from any chemicals as it affects brick quality.
  • They should be well burned.
  • The color of the bricks should be bright.
  • Bricks should be free from cracks and other flaws with sharp and square edges.
  • When the brick is struck with another brick, it should give a ringing sound.
  • They should not absorb water more than 20% by weight.
  • Bricks should be sufficiently hard. There should be no impression on the surface of a brick when it is scratched with fingernails.
  • The shape of a brick should be uniform. The edges of a good brick should be sharp, straight, and at a right angle.
  • Bricks should be soundproof.
  • Bricks should not be overburnt.
  • The thermal conductivity of bricks should be less because the building constructed with bricks should be cool in summer and warm in winter.
  • Bricks should be hard and should not break when dropped from an approximately one-meter height.

Tests & Procedure of brick

Before using bricks some of the tests must be carried out from the laboratory to check their quality as per standards.

Compressive strength test

The minimum number of samples needed for compressive strength is five. The sample brick is immersed in water for twenty-four hours. The frog of the brick is filled up flush with 1:3 mortars and brick is stored under wet jute bags for 24 hours followed by immersion in tidy water for three days.


The samples are placed between the plates of the compression testing machine. The load is applied axially at a uniform rate of 14 N/mm2 and the maximum load at which the sample fails is noted for the determination of compressive strength of brick given by

Compressive strength = Maximum load at failure/ Loaded area of brick

Water absorption test

Dry the samples in a ventilated oven at a temperature level of 105 to 115 degrees till it attains substantially constant mass. Cool the samples to room temperature and the weight is (M1).

The sampling is totally dried as in preconditioning after that Immerse in clean water at a temperature level of 27 ± 2 degrees for 24 hours. After that take out the samples and clean out any traces of water with a wet cloth and evaluate the specimen. Complete the evaluation 3 minutes after the samples have been removed from the water and record the weight (M2).

Water absorption = (M1-M2)/ M1 X 100%

Efflorescence test

Firstly, the end of the bricks is put in the dish, the depth of immersion in water being 25mm. The entire arrangement is put in a warm well-ventilated room up to the time all the water in the dish is soaked up by the samples and the surplus water evaporates. The dish including the brick is covered with an appropriate glass cylinder to avoid excessive vaporization from the dish that may not happen.

After water-absorbing is completed and bricks appear to be dry, place a similar quantity of water in the dish and permit it to vaporize like above. Analyze the bricks for efflorescence after the second evaporation and report the outcomes.


From the above test evaluation efflorescence shall be reported as ‘nil’, ‘minor’, ‘medium’, heavy’ or ‘serious’ according to the following explanations.

  • Nil: When there is no percentage deposit of efflorescence.
  • Minor: When there is less than 10 percent of the exposed area of the brick is covered with a thin deposit of salts.
  • Moderate: When there is a heavier deposit than under ‘minor’ and covering to half of the exposed area of the brick surface but unaccompanied by a powdering of flaking of the surfaces.
  • Heavy: If the deposit of salts covers half or more of the exposed area of the brick surface but is unaccompanied by powdering or flaking of the surfaces this is heavy efflorescent.
  • Serious: At the serious condition there is a heavy deposit of salts in the form of powdering and/ or flaking of the exposed surfaces.