Q.: Specifications for a job I'm doing call for a troweled surface for air-entrained concrete flatwork. I've heard that air-entrained concrete shouldn't be troweled. How can I convince the architect that troweling is a mistake?
A.: Air-entrained concrete can be troweled. If the concrete will be exposed to freezing and thawing, however, finishers must avoid overfinishing the surface. Overfinishing may drive air out of the surface layer and cause scaling of the concrete when it's exposed to freezing and deicing agents.
You might ask the architect why a troweled surface was specified. Simply striking off the surface and brooming it reduces the chances of overfinishing and will produce the most durable surface for concrete exposed to freezing and thawing. And a broomed surface is less likely to cause slip-and-fall accidents when the surface is wet.