Curing Concrete

Curing Concrete

Concrete must be kept moist for several days after it is placed to allow the portland cement in the mix to cure and harden properly. The most common methods of curing concrete are as follows:

• Cover the surface completely with large sheets of plastic. Be sure to keep the plastic flat on the surface of the concrete, or it will cause uneven coloring. Weight down edges and joints with pieces of lumber.
• Cover the surface with roofing felt. Tape the joints and edges or weight them down with pieces of lumber to help seal moisture in and retard evaporation.
• Cover the surface with burlap bags, using a garden hose to keep the bags wet.
• Sprinkle or fog the concrete with a garden hose or sprinkler.
• Apply a chemical curing compound.

Plastic sheeting and roofing felt can cause uneven discoloration of the concrete surface if they are not kept flat. On large surfaces, it is difficult to smooth out all of the wrinkles in a covering, so if the concrete will be exposed to view and its appearance is important, use another method for curing. Wet burlap curing should not be used on colored concrete surfaces because it can cause the color to become splotchy. Keep the concrete moist for seven days.

After concrete slabs have cured for 24 hours, and concrete walls and footings for three days, remove the forms, but do not pry or hammer against the concrete itself. The concrete will continue to cure slowly for another month until it reaches full strength, but slabs are safe to use for foot traffic after the first day and for light rubber-tired vehicles after the first week. Heavy traffic areas should be protected with plywood. Foundation walls and footings should cure for at least two weeks before substantial framing loads are added.