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close this bookBetter Farming Series 04 - The Soil: How the Soil is Made up (FAO - INADES, 1976, 37 p.)
close this folderWhat is soil made of ?
close this folderClay
View the document(introduction...)
View the documentClay soils


Adobe walls and pots are made of earth.
This earth is called clay.
Usually the clay is found in the third soil layer: the red layer.
Because of this, a hole has often to be dug to get earth for bricks.
Usually the clay is mixed, which is what gives it a red or sometimes a brown or black colour.
When the clay is not mixed, it is white. This is kaolin. It is pure clay. Kaolin is used to whitewash houses.

· Clay and water

Wet clay takes whatever shape it is given, such as bricks, pots and stoneware Jars.
Wet clay sticks to the fingers; it makes mud.
When it is dry, clay forms hard lumps.
If you crush a lump of clay, it becomes dust finer than flour.
When it is dry, brown or black clay loses its water and cracks.
Red clay also loses its water, but does not crack.
Red clay can be used to make bricks and stoneware jars.
If dry clay is made wet again, it becomes soft and sticky.
If clay is baked, it becomes very hard. The stoneware jars keep their shape.

Clay is impermeable.

Take a can.
Make a hole in the bottom of it.
Fill the can with clay.
If you pour water on to the clay, it does not go through.
We say clay is impermeable because it does not let water through.

Water does not go through

Clay in the soil

Almost all soils contain clay.
Soils that contain a lot of clay are called clay soils,