Concrete slabs should be 4 inches thick for normal residential construction. A slab should be 5 to 6 inches thick if heavy vehicles, such as motor homes or garbage trucks, will be parked on the concrete slab.
In order for the concrete slab to last, it is important to properly prepare the base by first removing all organic material. Next, gravel or sandy soil is added to build up the grade as necessary and then the base is compacted. Also, the base should be scraped away from the forms so that the edges of the concrete slab will be the full thickness in order to prevent cracking.