HARMFUL INGREDIENTS IN BRICK EARTH

1- LIME

• If Lime is present in excess , colour of bricks changes from Red to Yellow 
• When lime is present in lumps, it absorbs moisture , swells and causes disintegration of the bricks. Hence lime should be present in finely divided state , and lumps should be removed in the beginning itself 

2- IRON PYRITES 

• IF IRON PYRITES ARE PRESENT IN BRICK earth , then bricks tend to oxidise and decompose during burning and may split into pieces 
• PYRITES discolourise the brick 

3 - PEBBLES , GRAVELS , GRITS 

• BRICKS containing pebbles will not break regularly as desired.
• It does not allows clay to be mixed uniformly and thoroughly which will result in weak and porous bricks .

4 - ALKALIES 

• Excess of alkalies causes brick to melt and loose their shape 
• These causes Efflorescence- When bricks comes in contact with moisture , water is absorbed and the alkalies crystallise. On drying , the moisture evaporates , leaving behind gray or white powder deposit on the brick which spoil the appearance and this phenomenon is called as efforescence . 

5 - ORGANIC MATTER 

• During burning of bricks, organic matter gets burnt completely , leaving behind pores and hence making bricks porous .
• It also absorbs water and therefore reduces strength of brick. 

6- WATER

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

7 SULPHUR 

• IF sulphur is present in 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