Viewing post #575211 by growitall

Frillylily said:In the summer during drought times the clay dries out severely and shrinks away from the foundation which is supposed to be around the foundation to support it. With the clay shrinking, it can cause your slab to settle/crack. Some people go out and water their house around the foundation to prevent this. S

This happens when certain types of clay are present in the soil, aptly referred to as "swelling clays", often the result of deposition in ancient lake beds. The crystal structure of these particular clay minerals (montmorillonite, smectite, etc.) causes an expansion in volume when the clay takes up water, and shrinkage when it dries out again, just as you described. Swelling clays can be hell on basements where they occur, but, fortunately, they're not everywhere.