Clay Properties

Clay is the result of a long process of erosion, decomposition, and weathering, a material in its final stage that is in chemical equilibrium with the atmosphere. Just as cement is the binding agent for concrete, clays are the binding agents for earth.

The outer layer of planet Earth consists of three main layers: The uppermost layer is humus where most of our plants root and rot. Humus cannot be used for building as it is an organic material and as such part of a process. The middle layer, below the humus and above the rock of the Earth’s crust, consists of material eroded by natural processes. The more this material is eroded and sedimented, the finer its grains become. The finest grains are called clay particles (the larger ones sand, grit, and gravel). The larger grains are embedded in the fine clay particles, which glue them together by capillary action.

Molding clay into the desired form requires more water than is needed in its final state. During the drying process, the water evaporates, leading to significant shrinkage compared to other building materials. That is why earthen materials used for construction are often supplemented with other, preferably natural, materials like straw, hemp, sand, grit, stones, and such like.