Q.: How do you overcome a rubber-like movement when troweling?

A.: This phenomenon sometimes occurs when the surface of the concrete is drying very rapidly and seems to be setting while the concrete underneath is not setting. I occurs under the same kind of conditions that sometimes contribute to plastic shrinkage cracking and is more likely with an air-entrained mix than with a non-airentrained mix.

The remedy is to keep the top surface of the concrete from drying. Immediately after placing, striking off and bull-floating or darbying, the finisher should cover the surface with wet burlap. Polyethylene sheet does not work as well. The burlap should then be kept continuously moist with a fine spray from a hose. Care shout be taken to see that the burlap is continually saturated without worrying about getting it too wet but without producing puddles. The burlap should be removed little at a time for the operations of floating and troweling