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Coverage Rate &Timing when Applying Color Hardener

By Chris Sullivan – ChemSystems, Inc.

Question:

I poured an 800-square-foot residential patio and colored it using a cream-colored dry-shake hardener. After applying eight pails of color hardener, I was still able to see blotches of gray where the color didn't cover completely. I followed the recommended application rate, so why do I still see gray? And how can I hide the gray areas and make the patio more uniform for the homeowner?

Answer:

Average coverage rates for dry-shake color hardener range from 1/2 to 1 pound per square foot, depending on the opacity, or hiding ability, of the color. Lighter colors have less opacity, thus require a higher dosage rate to achieve uniform, total coverage. Conversely, darker colors hide better and require less material to achieve total coverage. In general, I recommend that contractors plan on using 3/4 to 1 pound of color hardener per square foot. It's always better to have leftover material than to run short with 30 feet to go!

While coverage rate is important, the real key to achieving uniform and complete color coverage with dry-shake hardener is proper execution, especially the timing of application. If the concrete is too wet when you apply the hardener, most of the color will be lost because it will be worked down into the wet concrete with the float. I believe this is what occurred with the patio in question. Even though you applied a full pound of color hardener per square foot, blotchy gray areas remained. And there wasn't much you could do to remedy the situation before the slab hardened because all the material planned for the job had been used.

There are two methods for fixing this problem. The first is to apply a coating in a matching color to help hide the gray areas. Options include a color wax, colored curing membrane, colored cure-and-seal, or colored sealer. While these are relatively quick and cost-effective fixes, they aren't permanent and will require occasional application of maintenance coats to rejuvenate the color. The other fix involves applying a thin overlay, or microtopping, to the entire surface. This is more costly and time consuming than applying a colored coating, but the results are more permanent and the surface requires very little maintenance. Both of these remedial measures should be sampled and the pros and cons explained to the homeowner prior to installation.

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