Posted on March 02,2015 by user-756436 in blotter sand
What goes under the concrete in a slab-on-grade home? In the old days, not much — just dirt. Eventually, contractors discovered that it made sense to include a 4-inch-thick layer of crushed stone under the concrete. The crushed stone provides a capillary break that reduces the amount of moisture flowing upward from the damp soil to the permeable concrete.
Since the crushed stone layer provides a fairly uniform substrate, it also may also reduce the chance that a concrete slab will be poorly supported by random pockets of soft, easily compressible soil.