Quality Requirements of Common Burnt Clay Timbers

1. General Quality

  • Bricks should be free from cracks and defects and free from lumps of lime.
  • Bricks will have smooth rectangular faces with sharp corners
  • bricks are of the same color
  • The frog shape of a hand cast brick with a height of 90 mm or 70 mm will be as shown in the figure below.
Frog Shape for Common Burnt Clay Building Bricks
Frog Shape for Common Burnt Clay Building Bricks

2. Dimensional Specification

Bricks can be of modular shape or non-modular shape. The size of the individual brick should correspond to the dimensions given in the following table.

Dimensions for Modular Bricks
Length (L), mm Width (W), mm Height (H), mm
190 90 90
190 90 40
Dimensions for non-modular bricks
Length (L), mm Width (W), mm Height (H), mm
230 110 70
230 110 30

3. Physiological Requirements

When tested for physical characteristics of ordinary clay building bricks, they must meet the following quality requirements, as set out in the table below.

pressure force The compressive strength of any one brick shall not be less than the minimum compressive strength for the class of brick concerned. (see Table below)
water absorption Not more than 20% by weight up to class 12.5 and 15% by weight for higher classes.
flourish The class should not exceed ‘Medium’ till 12.5 and ‘Moderate’ for the upper class.

4. Classes of Common Burnt Clay Bricks

On the basis of its average compressive strength, bricks are classified into the following classes as shown in the table below. When tested for a compressive strength test, the brick must fall into any of the following classes.

class designation average compressive strength
n/mm2 kg/cm2, (About)
35 35 350
30 30 300
25 25 250
20 20 200
17.5 17.5 175
15 15 150
12.5 12.5 125
10 10 100
7.5 7.5 75
5 5 50
3.5 3.5 35


IS: 1077-1992

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.