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Concrete Curing Compound Application Rate
Fresh concrete must be cured for 3 to 7 days to fully hydrate and reach its maximum strength.
Applying curing compound at the manufacturer’s suggested rate will ensure that moisture for hydration remains and excess moisture escapes.
If you want the concrete you pour to have maximum strength and durability, you must make sure it is cured properly. You can do this by maintaining the right moisture content in the concrete during the first seven days after it is placed (three days for high early-strength concrete).
If you want the concrete you pour to have maximum strength and durability, you must make sure it is cured properly. You can do this by maintaining the right moisture content in the concrete during the first seven days after it is placed (three days for high early-strength concrete).
The cement in a concrete mix requires only 22 to 28% of its weight in water to properly hydrate and harden. But concrete at that water-cement ratio would be so dry you could not work it, let alone get it to come out of the mixer. You must have additional water in the concrete mix at the time it is poured to make it workable. This additional water typically amounts to 8 to 10 gallons in a cubic yard of concrete. That means 8 to 10 gallons of water that must be allowed to escape the concrete so it can cure. You don’t want too much moisture to escape, however, because the moisture content must be maintained at a level that allows the concrete to hydrate properly.
Most of the excess water comes to the surface by capillary action, or bleeding, when the concrete is consolidated, leveled, and finished. Once on the surface it evaporates. Your job is to find a way to control the amount of water that escapes.
Many methods and materials are available for slowing the evaporation from the concrete surface. The most common is liquid-membrane curing. The ACI (American Concrete Institute) also lists other methods, such as ponding water on the surface, misting with soaker hoses, and covering with wet burlap or other moisture-retaining sheet materials. However, liquid-membrane curing is probably the most cost-effective method.
Liquid-membrane forming compounds are commonly formulated to ASTM C-309 standards, which allow a maximum moisture loss of .055 grams per square centimeter in 72 hours. However, we have observed on many job sites that the curing compound is not applied as recommended by the manufacturer.
Typically, a two-gallon (7.5 L) spray can is filled with compound and sprayed on a house slab until the can is empty. The problem is that most curing compounds are intended to be applied at 200-300 square feet per gallon(4.9-7.4 square meters per liter), and a typical house slab may have well over 1000 square feet (93 square meters) of concrete. A two-gallon spray can in that case would only provide half the rate of coverage intended by the manufacturer.
Read the label. Guesstimate how much you will need to apply based on the instructions and the square footage (area) you have. Apply the recommended amount, and you will have a moisture barrier equivalent to the manufacturer’s recommendation.