I poured a concrete drive, dusted and floated in black Colorundum, and sprayed with "60 D" curing compound. There were about five pours involved to complete the driveway. Some pours were rained on during the night after the pouring. In varying degrees, white powdery material formed on the black surface. It seems that where the water accumulated in puddles, the white material is heaviest. I have tried numerous cleaning materials--wax removers, commercial cleaners, naphtha, and muriatic acid (which pulled the black out of the concrete) and still no solution was found. The driveway is large--approximately 3,500 feet--so an inexpensive treatment is needed, if that is possible.
While it is difficult to prescribe a ready-made cure without seeing the job, the problem was probably caused by overfinishing a somewhat wet concrete, resulting in efflorescence. We know nothing about black Colorundum, which may or may not be lime-fast. The information that the white material is heaviest where the water accumulated may indicate efflorescence due to lime or alkalis. The best we can suggest is to get technical advice from the manufacturer of the cement used or from the local Portland Cement Association office.