Are special soils required to make adobe bricks?
Almost any soil will make usable adobe bricks. Nearly all naturally occurring soils have rocks, sand, silt, and clay, in varying proportions. If the rocks are too large, approaching the thickness of the brick, they should be removed. Some soil has no rocks at all, and may be mostly sand, which can be coarse or fine. Silt is a flour fine powder of ground rock. The clay is the “glue” or binding agent that holds the mix together and makes the bricks more resistant to wetting. The clay can be one of several types, some of which expand when wet, shrink when drying, and some are inert. The majority of soils found around the world have too much clay, which may produce shrinkage cracks while drying. This can be corrected or reduced by adding either sand or straw. The quantity to be added must be determined by trial and error. The best test for determining the suitability of a soil for bricks is to make a few test bricks. The proportions of sand, silt and clay can vary widely, and still make a
