Constituents of Good Brick Earth

Bricks are the most normally used construction material. Bricks are prepared by moulding clay in rectangular blocks of uniform size and then drying and burning these blocks. In order to get a good quality brick, the brick earth should contain the following materials so lets know about “Constituents of Good Brick Earth

  • Silica
  • Alumina
  • Lime
  • Iron oxide
  • Magnesia

Constituents of Good Brick Earth


  • Brick earth should contain about 50 to 60% of silica.
  • It is responsible for preventing cracking, shrinking and warping of raw bricks.
  • It also affects the durability of bricks.
  • If present in excess, then it destroys the cohesion between particles and the brick becomes brittle.


  • Good brick earth should contain about 20% to 30% of alumina.
  • It is responsible for plasticity characteristic of earth, which is important in moulding operation.
  • If present in excess, then the raw brick shrink and warp during drying.


  • The percentage of lime should be in the range of 5% to 10% in good brick earth.
  • It prevents shrinkage of bricks on drying.
  • It causes silica in clay to melt on burning and thus helps to bind it.
  • Excess of lime causes the brick to melt and brick loses its shape.

Iron oxide

  • Good brick earth should contain about 5% to 7% of iron oxide.
  • It gives a red colour to the bricks.
  • It improves impermeability and durability.
  • It gives strength and hardness.
  • If present in excess, then the colour of brick becomes dark blue or blackish.
  • If the quantity of iron oxide is comparatively less, the brick becomes yellowish in


  • Good brick earth should contain less a small quantity of magnesia about1%)
  • Magnesium in brick earth imparts a yellow tint to the brick.
  • It is responsible for reducing shrinkage
  • Excess of magnesia leads to the decay of bricks.

Harmful Ingredients in Brick

Harmful Ingredients in Brick


Below mentioned are some of the ingredients which are undesired in brick earth.


  • A small quantity of lime is required in brick earth. But if present in excess, it causes the brick to melt and hence brick loses its shape.
  • If lime is present in the form of lumps, then it is converted into quick lime after burning. This quick lime slakes and expands in presence of moisture, causing splitting of bricks into pieces.

Iron pyrites

  • The presence of iron pyrites in brick earth causes the brick to get crystallized and disintegrated during burning, because of the oxidation of the iron pyrites.
  • Pyrites discolourise the bricks.


  • These exist in the brick-earth in the form of soda and potash. It acts as a flux in the kiln during burning and it causes bricks to fuse, twist and warp. Because of this, bricks are melted and they lose their shape.
  • The alkalis remaining in bricks will absorb moisture from the atmosphere when bricks are used in masonry. With the passage of time, the moisture gets evaporated leaving grey or white deposits on the wall surface (known as efflorescence). This white patch affects the appearance of the building structure.


  • Pebbles in brick earth create a problem during mixing operation of the earth. It prevents uniform and thorough mixing of clay, which results in weak and porous bricks
  • Bricks containing pebbles will not break into shapes as per requirements.

Vegetation and Organic Matter

  • The presence of vegetation and organic matter in brick earth assists in burning. But if such matter is not completely burnt, the bricks become porous. This is due to the fact that the gasses will be evolved during the burning of the carbonaceous matter and it will result in the formation of small pores.


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