Composition of Brick Earth
the main constituents of Earth for brick making are
Silica or Sand
A good brick earth contains about 50% to 60% of silica.
Alumina or Clay
A good brick earth contains about 20% to 30% of alumina.
Lime
A good brick earth contains up to 5% of lime.
Magnesia
A good brick earth contains up to 3% of magnesia. It is used for decreasing the shrinkage of bricks.
Oxide of Iron
A good brick earth contains up to 6% of iron oxide. It helps lime to fuse is silica and gives red colour to the bricks.
it may be noted that
(a) The excess of alumina in the clay (brick earth) makes the brick crack and warp during drying process.
(b) The excess of silica in the clay makes the brick brittle and weak after burning.
(c) The excess of lime in the clay causes the bricks to melt and distort during burning.
(d) The alkaline salt present in the bricks, absorb moisture from air which on drying leaves powder deposit on the brick
(e) This effect is known as efflorescence. It is also caused if the clay used for making bricks contain pyrite and the water used for pugging the clay contain gypsum.
Manufacturing of Bricks
Preparation of Clay
(I) After removal of vegetation, the clay deposit is excavated in steps rather than in layers to ensure a better distribution of the several constituents which vary in different proportions at different depths.Further processing of the clay depends on the type of bricks to be made.
(ii) For ordinary country bricks, very little preparation. except mixing by treading is resorted to.
(iii) For making first class facing bricks, the clay is allowed to weather by keeping it exposed to open air for a considerable period, so that the lumps of clay break down into smaller particles and get matured.
(iv) As a further refinement for making very superior bricks, the clay is washed and processed before moulding into bricks.
(v) For making clay tiles also we use the clay that has been processed.
