Defects In Bricks ,Brick Earth Composition:

Defects in bricks

Over burning of bricks:

Bricks should be burned at temperatures at which incipient complete and viscous verification occur. However, if the bricks are over burnt, a soft molten mass is produced and the bricks lose their shape. Such bricks are not used for construction works.

Under burning of bricks:

 When bricks are not burnt to cause complete verification, the clay is not softened because of insufficient heat and the pores are not closed. These results in higher degree of water absorption and less compressive strength  . Such bricks are not recommended for construction works.

Bloating:

 This defect observed as spongy swollen mass over the surface of burned bricks is Caused due to the presence of excess carbonaceous matter and sulphur in brick-clay

Black core:

 When brick-clay contains bituminous matter or carbon and they are not completely removed by oxidation, the brick results in black core mainly because of improper burning.

Efflorescence:

 This defect is caused because of alkalis present in bricks. When bricks come in contact with moisture, water is absorbed and the alkalis crystalize. On drying grey or white powder patches appear on the brick surface.

Chuffs:

 The deformation of the shape of bricks caused by the rain water falling on hot bricks is known as chuffs

Spots:

 Iron sulphide, if present in the brick clay, results in dark surface spots on the brick surfaces. Such bricks though not harmful are unsuitable for exposed masonry work.

Blisters:

 Broken blisters are generally caused on the surface of sewer pipes and drain tiles due to air imprisoned during their moulding.

Brick Earth Composition:

For the preparation of bricks, clay or other suitable earth is moulded to the desired shape after subjecting it to several processes. After drying, it should not shrink and no crack should develop. The clay used for brick making consists mainly of silica and alumina mixed in such a proportion that the clay becomes plastic when water is added to it. It also consists of small proportions of lime, iron, manganese, sulphur, etc

The proportions of various ingredients are as follows:

Silica	50 to 60%
Alumina	20  to 30%
Lime	10%
Magnesia	less than 1%
Ferric oxide	less than 7%
Alkalis	less than 10%