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Harmful Ingredients in Bricks

1. Lime

  • If lime is present in excess, the colour of brick changes from Red to Yellow.
  • Lime is present in lumps (limestone, kankar) converted into quicklime after burning and this quicklime slakes and expands to 2 to 3 times its volume in presence of moisture, it absorbs moisture, swells, and causes disintegration of the bricks. Hence lime should be present in a finely divided state, and lumps should be removed at the beginning itself.
2. Alkalies
  • They are mainly present in form of soda and Potash, are of great value as fluxes.
  • Alkalies in excess lower the fusion temperature resulting in twisting and warping of bricks. Hence bricks lose their shape.
  • These causes Efflorescence i.e., When bricks come in contact with moisture, water is absorbed and the alkalies crystallise. On drying, the moisture evaporates, leaving behind grey or white deposits on the brick surface which spoil the appearance. This phenomenon is called efflorescence.
Efflorescence of Brick

3. Sulphur

  • If it is present in the brick earth and insufficient time is given (during burning) for oxidation of carbon and sulphur, then sulphur will cause the formation of a spongy, swollen structure in the brick and the brick will be decoloured by white blotches.

4. Water

  • A large amount of free water causes shrinkage of bricks on drying, whereas combined water causes shrinkage during burning.

5. Iron Pyrites

  • Iron pyrites if present in raw material, decompose, oxidize, and finally crystallize in the brick causing it to split. 
  • Pyrites discolourise the bricks.

6. Pebbles, Gravels, Grits

  • It does not allow the clay to be mixed uniformly and thoroughly which will result in weak and porous bricks.

7. Organic Matter

  • The presence of the organic matter in the raw material help in burning the brick but if not thoroughly burnt may result in porous bricks due to entrapping of gases evolved by the burning of carbonaceous matter present in the raw materials. Hence, thorough burning of brick is necessary.
  • It also absorbs water and reduces the strength of brick.

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