A Monolithic slab is a slab foundation that is part of the footings. For a slab foundation, the site is leveled off, and a trench is dug around the perimeter of the home site. Gravel is then spread across the site, and concrete is poured approximately four inches thick over wire mesh and a moisture barrier. In areas of load bearing walls, trenches need to be dug to allow for additional thickness at this location. slab foundations have no piers or floor joists, and the concrete slab is the floor system.