Q: I am patching and repairing some existing concrete curbs and sidewalks that are a light sandy color. The quick-mix patching products tend to be dark gray, which does not match well at all. How can I get the repair concrete to be a better match?
A: This kind of patching is harder than you might think. One difficulty of color-matching patches is the fact that the existing concrete isn't just one color, and the variations become more obvious when you add a one-color patch. Here are some suggestions.
Get a commercial polymer patching product made with white portland cement, then add a little regular cement to deepen the color. Patching cements often look darker than the color of the cement alone because they contain polymer bonding agents that make the concrete denser.
Tint the patch mix with water-based, metallic oxide pigments for concrete, which are available at paint stores and construction supply houses. You can buy a full range of colors, including white. Colors that come in liquid form work especially well for this.
Add a light-colored pozzolan called metakaolin to your patch mix.
Keep trying and adjusting the mix until you find the right recipe.