Concrete is the most unforgiving material builders use. Once it has cured, mistakes are "set in stone" and are extremely difficult and costly to repair. But like any other part of the building process, with planning and coordination, you can ensure a quality product and minimize callbacks. Design A well-designed slab is sized for its intended use: The more demanding the use, the stronger the slab needs to be. Typical residential slabs for foot traffic, storage, and vehicle parking are 4 inches thick, but large, heavy vehicles — like loaded pickups, oil delivery trucks, and trash haulers — require a 5- or 6-inch slab. Parts of the slab may be thickened to support heavier loads, such as bearing walls or fireplaces (see