How to Cure Colored Concrete
Now let's narrow this conversation down a bit. Let's talk only about horizontal concrete and only about the moisture part of curing. To learn more about working in temperature extremes get a copy of ACI 305, Hot Weather Concreting or ACI 306, Cold Weather Concreting.
Let's also narrow things down to curing of colored concrete. We'll define that as any concrete with color, whether integral or dry-shake, whether it is going to be stamped or not. First, and most importantly, colored concrete is not really different than any other concrete, it needs exactly the same treatment to end up with quality concrete. Some of the methods, though, need to be a bit different since appearance is so much more important than it is for an industrial slab.
There are three ways to cure concrete: either we add water to the surface to replace the water that is evaporating or we seal the concrete to prevent the water from evaporating in the first place or we do both. Note that adding water to the surface is NOT adding water that will be worked into the concrete mix--that would increase the water-cement ratio of the surface concrete and weaken it, ruining all our curing efforts.
You need to think about initial curing when the bleed water is evaporating too rapidly to keep the surface wet prior to initial set. Traditionally that has been specified at greater than 0.2 pounds per square foot per hour. Many mixes today bleed at much lower rates than this, so if there is less bleed water then the evaporation limit needs to be set lower—more like 0.05 to 0.1 pounds per square foot per hour. The best approach for decorative concrete is to try to alter conditions so you don't need to do initial curing: block the wind, keep the sun off the concrete, get cooler concrete. If that's not possible, fogging just enough to keep the surface damp is possible, but the simplest approach is to use evaporation retardant. This chemical can be sprayed on to form a thin membrane on the surface that prevents the water from evaporating. It completely dissipates during finishing operations. Keep some of this around for dry windy conditions.
Now, at last, let's get to final curing.
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