Short answer
Curing keeps new concrete moist and warm enough to keep gaining strength. NRMCA says it should start right after finishing and continue at least 3 to 7 days, with the concrete kept above 50°F. Concrete left to dry out can lose as much as 50% of its potential strength compared with moist-cured concrete.
Key facts
- Cure for at least 3 to 7 days, starting right after placement and finishing (NRMCA CIP 11)
- Keep placed concrete above 50°F (NRMCA CIP 11)
- Concrete in a dry environment can lose up to 50% of its potential strength (NRMCA CIP 11)
- Alternate wetting and drying is not acceptable curing (NRMCA CIP 11)
- Use reflective (white) plastic sheeting in warm weather (NRMCA CIP 11)
Why it matters
NRMCA explains that cement only gains strength while it has water to react with. Well-cured concrete has a harder surface, cracks less, and keeps water and chemicals out better. Poor curing leads to a weaker surface and more crazing, dusting and scaling.
How it is done
Methods that add water: fogging or sprinkling, ponding, or wet burlap kept wet. NRMCA warns that alternate wetting and drying is not an acceptable curing practice.
Methods that hold water in: plastic sheeting at least 4 mils thick laid tight to the surface, with white reflective sheets in warm weather, or a liquid curing compound sprayed on once the surface sheen is gone. NRMCA notes plastic can leave dark streaks where it wrinkles, so it is not used where appearance matters.
What you can do
Ask what curing method is planned and for how long. Keep sprinklers from cycling the slab wet and dry, keep traffic off until your contractor clears it, and remember that hot Central Valley days dry concrete fast.
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