How Long Does Concrete Take to Cure? 7 Days Moist, 28 Days to Strength

New Concrete: What You Can Do, and When

For a standard mix in mild weather, measured from the pour. Each time is the shortest its publisher states, at the temperature it states.

Curing Is Keeping It Wet, Not Letting It Dry

Concrete hardens because cement reacts with water, not because the water evaporates. Curing means holding moisture and a moderate temperature in the slab while that reaction runs. NRMCA’s Concrete in Practice 11 says curing should begin immediately after placement and finishing, that the concrete should be kept above 50°F, and that concrete in a dry environment can lose as much as 50 percent of its potential strength compared with moist-cured concrete. Alternate wetting and drying, it says, is not an acceptable curing practice.

The usual methods are plastic sheeting (CIP 11 says at least 4 mils thick), wet burlap kept damp, or a liquid curing compound sprayed on after finishing. Covering a 20x20 slab with 6-mil polyethylene costs about $29 in sheeting at Menards’ roll price. In hot weather, NRMCA’s CIP 12 says to continue curing for at least 3 days and notes that concrete cured hot at an early age ends up weaker than the same concrete cured near 70°F.

How Fast Concrete Gains Strength

Makers publish compressive strength at set ages (ASTM C39 cylinder tests). These are lab figures for each bagged mix, not a promise for your slab, but they show the shape: most of the strength comes in the first week, and the rest by 28 days.

The 28-day figure is the one that counts in a contract. The American Concrete Institute notes that under ACI 318-19 the specified compressive strength is based on 28-day tests unless the construction documents say otherwise, and that 3- and 7-day results are used to monitor early strength, not for acceptance. NRMCA’s CIP 35 says compressive strength can vary from 2,500 psi for residential concrete to 4,000 psi and higher in commercial structures. If you are choosing a mix, see 3,000 PSI concrete cost and 4,000 PSI concrete cost.

Cold and Hot Weather Change the Clock

Cold. NRMCA’s CIP 27 defines cold weather as more than 3 days in a row averaging below 40°F. Fresh concrete freezes below about 25°F, and frozen concrete can lose more than half its potential strength. It should be protected until it reaches 500 psi, about two days after placement, and a 20°F drop in concrete temperature roughly doubles setting time. Concrete that will see freeze-thaw cycles should be protected from them until it reaches at least 3,500 psi. Quikrete says to protect its mix from freezing for the first 48 hours and to use plastic and insulating blankets if temperatures are expected below 32°F.

Hot. Heat speeds setting and dries the surface. NRMCA’s CIP 12 says to keep curing for at least 3 days with wet burlap and plastic, a membrane curing compound or water. Pour early in the day and have the curing method ready before the truck arrives.

How Long a Concrete Slab Lasts

There is no published lifespan for a concrete driveway or patio from a primary source. The closest is the NAHB and Bank of America Home Equity Study of Life Expectancy of Home Components (February 2007), a survey of manufacturers, trade associations and researchers. It lists poured footings and foundations as lasting a lifetime if properly built, and concrete flooring at 50+ years. It has no driveway or patio entry and calls its figures a general guideline only.

What shortens a slab’s life is mostly set in the first week: a poorly compacted base (see site prep cost), joints cut too late, and curing skipped or cut short. When a slab has settled or cracked, compare mudjacking against replacement.

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