We make our own dry repair mixture for use on small patching jobs, but the sands in our area are coarse, making the repair mixture hard to finish. It also bleeds a lot. Someone recommended that I add fly ash to improve finishability and reduce bleeding. However, I've heard that fly ash retards setting, which would be undesirable when using the mix in cool weather. Is it possible to add fly ash without affecting the concrete setting time?
Fly ash doesn't chemically retard setting. But many times fly ash is used in concrete as a cement replacement in combination with a water reducer. These concretes set more slowly than a straight cement mix would. If you don't use fly ash to replace cement, but just to increase fines, it won't retard setting. It simply serves as an additional fine aggregate and makes your patching mix easier to finish and less likely to bleed excessively. If the patching mix must be air entrained, you will probably need more air-entraining agent to get the same air content as a mix that doesn't contain fly ash.