About this Project

Although concrete is very strong in many respects, it has limited tensile (lateral) strength. A slab without a firm, uniform base almost certainly will crack and heave unevenly, leaving you with a difficult repair job. This happens with driveways, for example, where the sand base underneath washes away, allowing the weight of vehicles to crack the slab. If possible, place concrete slabs on undisturbed soil -- soil that has never been dug up. In many areas, this means digging down until you reach clay. If you must pour a slab on top of recently dug soil, as would be the case with backfill from a foundation dig, pack the soil by watering it for several days and giving it time to settle. Then compact the earth, using a hand tamper for small areas or a rented vibrating tamper for larger areas.