Concrete Slab Prep Checklist

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The checklist

1. Confirm the dig. Excavate to firm, undisturbed soil. If you hit soft spots, dig them out and backfill with compacted stone — concrete poured over mush will settle and crack.
2. Base: 4–6 inches of compacted crushed stone. Compact in 2–3 inch lifts with a plate compactor or hand tamper. This is the single highest-leverage step; most cracked slabs trace back to a lazy base.
3. Forms: level, staked, braced. Set finished height with a string line and level — you can't fix a slope after the pour. Oil or form-release the inside faces so forms strip cleanly.
4. Reinforcement in place. Rebar or welded wire mesh, chaired up so it sits in the middle of the slab — steel lying on the dirt does nothing. Overlap bars 12 inches, tie intersections.
5. Drainage slope: 1/8 to 1/4 inch per foot away from the house. Water pooling against a foundation is a slow-motion disaster.
6. Control joints planned. Cut or tooled joints every 8–12 feet (rule of thumb: joint spacing ≈ 2–3× slab thickness in feet for a 4″ slab). Concrete cracks — joints decide where.
7. Order 5–10% extra (run the concrete calculator first) and have the truck's number saved. Coming up short is the one mistake you can't undo.
8. Cure it. Keep it damp for at least 3–7 days — misting, wet burlap, or curing compound. Concrete that dries out in the first 48 hours never reaches its design strength.

Mistakes that crack slabs

• Adding extra water at the truck "to make it flow" — every gallon of water weakens the mix. Order the right slump instead.
• Skipping the gravel base on "good" soil. Soil moves; stone distributes.
• No control joints, or joints cut too late (within 24 hours of the pour, or tooled while wet).
• Pouring on frozen ground or in a downpour.

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