Curing and Drying Time for Concrete Footers

Purpose of Curing

• The two major reasons for curing concrete are strength and shrink resistance. Curing keeps moisture in the poured concrete to allow it to dry slowly and increase its resilience, water tolerance and resistance to surface wear. The slow drying also deters rapid shrinkage, which makes concrete develop cracks and fissures.

Curing Methods and Times

• Curing is done through various methods. You can flood the footer or spray it with a fine mist to keep it wet during curing. Covering the footer with wet straw, burlap, sand or canvas keeps in the moisture but requires periodic rewetting to be effective. Plastic films or waterproof paper promote curing but may cause splotches on the concrete surface. Chemical membranes keep the concrete wet and impart it with substances to increase its strength. Whatever method is used, concrete generally needs to be allowed to cure over three to seven days. Once the concrete cures for seven days, it is about 50 percent stronger than uncured concrete.

Concrete Drying Times

• Although the curing process dries out the interior of the concrete, the exterior and final drying begins when no water is visible on the concrete surface. Several pounds of water have to evaporate from each square foot of concrete footers before they are sturdy enough to support walls or columns. A footing for a two-story residential building is typically 8 to 10 inches thick, and drying times depend on the type of concrete used as well as the temperature and humidity in the area.

Tips and Hints

• To increase water retention during curing, build soil dams around the footers before flooding them. If possible, pour the footers at the end of the work week so the curing continues through the weekend and less labor time is lost. If you are unsure if the curing and drying are adequate, drill a hole in the footer and measure the moisture content with a relative humidity probe. Avoid pouring footers in extremely hot or cold weather conditions, as these will significantly affect the curing and drying processes.