The ingredient of brick earth enabling the brick to retain their shape is

Composition of good brick earth:

1) Silica

A good brick earth should contain 50 – 60% of silica.

It prevents cracking, shrinking and wrapping of raw bricks.

Silica imparts uniform shape to the bricks.

Excess of silica make the bricks brittle.

2) Alumina

A good brick earth should contain 20 – 30% of Alumina.

Alumina imparts plasticity to the earth, so that it can be moulded.

If it is excess raw bricks shrink and wrap during drying and burning.

3) Lime

It should not be greater than 5% for good bricks

4) Iron oxides

It should be in the range of 5 – 6% for the good bricks.

5) Magnesia

It imparts colour to the brick.

It also deceases shrinkage in the bricks.