Following are the ingredients which are undesirable in the brick material-- Lime
- Alkalies
- Pebbles
- Iron pyrites
- Vegetation and Organic matter
1. LIME
- If lime in brick earth present in excess, it causes the brick to melt and hence brick looses 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.
2. ALKALIES
- Alkalies exist in the brick in the form of soda and potash
- Alkalies present in the brick earth lower the fusion temperature abnormally as a result of which the brick deforms and twist.
- Alkalies remaining in bricks will absorb water from the atmosphere. When the moisture gets evaporated leaving grey or white deposits on wall surface (efflorescence) which affects the appearance of the building structure.
3. PEBBLES
- It prevents mixing of clay thoroughly and uniformly, which results in weak and porous bricks.
- Bricks containing pebbles will not break into shapes as per requirements.
4. IRON PYRITES
- If the iron pyrites present in brick earth causes the brick to get crystallized and disintegrated during burning, because of the oxidation of the iron pyrites.
5. 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.
