Preparation of brick earth

 

1. Unsoiling

The soil used for making building bricks

should be processed so as to be free of

gravel, coarse sand (practical size more

than 2 mm), lime and kankar particles,

organic matter, etc. About 20 cm of the

top layer of the earth, normally containing

stones, pebbles, gravel, roots, etc., is

removed after clearing the trees and

vegetation.

2. Digging

After removing the top layer of the earth,

proportions of additives such as fly ash,

sandy loam, rice husk ash, stone dust, etc.

should be spread over the plane ground

surface on a volume basis. The soil mass

is then manually excavated, puddled,

watered and leftover for weathering and

subsequent processing.

3. Weathering

The soil is left in heaps and exposed to

the weather for at least one month in

cases where such weathering is

considered necessary for the soil. This is

done to develop homogeneity in the mass

of soil, particularly if they are from

different sources, and also to eliminate

the impurities which get oxidized. The

plasticity and strength of the clay are

improved by exposing the clay to weather.

4. Blending

The earth is then mixed with sandy-earth

and calcareous-earth in suitable

proportions to modify the composition of

the soil. A moderate amount of water is

mixed so as to obtain the right

consistency for moulding.

5. Tempering

It is done in pug mill and the process is

called pugging. Tempering consists of

kneading the earth with feet so as to make

the mass stiff and plastics (by plasticity,

we mean the property which wet clay has

of being permanently deformed without

cracking). It should preferably be carried

out by storing the soil in a cool place in

layers of about 30 cm thickness for not

less than 36 hours.

6. Moulding

It is a process of giving a required shape

to the brick from the prepared brick earth.

Moulding may be carried out by hand or

by machines.

7. Drying

The object of drying is to remove the

moisture to control the shrinkage and

save fuel and time during burning.

8. Burning

The burning of clay may be divided into

three main stages: Dehydration stage

(400 - 650°C), Oxidation period (650 -

900°C), vitrification. Burning of bricks is

done either in clamps or kilns.