Fixing Dusty Concrete
Q: "A storm drenched a basement floor before it cured. How can it be fixed?"
My son had just finished pouring his basement floor when a storm came along and thoroughly drenched the slab before it had cured. He was able to smooth out the surface, but now the concrete is dusty and scratches easily. What can he do about it?
— Bruce, Dresden, ME
Tom Silva replies: This problem is caused when concrete is troweled while its surface is still covered with a film of water—rain, in this case. It forces water back into the concrete, creating a surface layer that turns powdery when it dries. He might have been able to skim off the excess water with the edge of a long piece of siding, or by dragging a hose across the surface, but even though he didn't, all is not lost.
Your son can still coat the floor with a concrete sealer to keep the floor from dusting. My concrete finisher uses a deep-penetrating acrylic sealer, which he applies after first pressure-washing the floor and allowing it to dry.