When you hear about curing concrete it can mean different things. Curing is letting concrete grow into its full potential by keeping it moist and at the right temperature so that the cement can hydrate. The critical part of curing, though, is on a slab surface (its skin, so to speak--don’t let it get chapped!).
1) When concrete is initially placed it’s like a newborn baby — it must be kept warm, but not too warm. While human babies need to be dry, our concrete baby needs to be wet. All of the concrete needs to be treated with care but usually there’s plenty of moisture inside — it’s the surfaces that are most at risk.
2) If our concrete baby’s skin gets dry, the cement doesn’t hydrate, resulting in low strength at the surface. It also makes the concrete more porous (higher permeability) — again, especially at the surface. Drying of the surface can also result in crazing and plastic shrinkage cracks.
3) Initial curing keeps the concrete surface from drying out before the concrete sets — usually only needed in dry, windy conditions. This is done by fogging or spraying on an evaporation retarder. This is followed by final curing to keep the surface from drying for several days while it gets stronger.
4) There are two ways to cure a concrete surface: Keep it damp or prevent it from drying out. To keep the surface damp, it can be misted with water or covered with curing blankets — some of the newer ones are very similar to a wet disposable diaper. This way of curing is ideal and has the advantage of leaving no residue on the surface.
5) The more common way to cure the surface is to spray on a curing compound that forms a thin membrane to prevent the moisture in the concrete from evaporating. This is sort of like putting the concrete inside a balloon and since there’s usually plenty of moisture in the wet concrete, as long as it can’t dry out, it will cure.
6) When we get the curing right, the surface will reach its full potential of strength and durability. Our concrete baby’s skin will be dense and hard and he will have grown up to become strong, reliable, and a good concrete citizen.