Q.: We are bidding on some city sidewalks where the specifications require that plastic sheet be used for curing. We know that this ordinarily causes white discoloration and we don't want to be held responsible. Is there any way to prevent the discoloration?

A.: You can't prevent white discoloration without going to another curing system either a liquid membrane curing compound or some kind of continuous wet curing. We suggest that you show the city a copy of the four-page article "Discolored Concrete Flatwork," published in our November 1967 issue, page 417, and argue that the city must either accept white discoloration, at least initially (white discoloration does slowly diminish over a considerable period of time), or approve a different curing method.