Q.: We do residential walks and driveways and we are always concerned about durability to freezing and thawing. I have been told that the entrained air can be troweled out of a surface if it is rubbed hard with float or trowel when the concrete is barely finishable. Is this so?

A.: Yes it is possible to knock air out of the surface by prolonged troweling. Nevertheless, hard troweling--repeated troweling of a surface that is barely finishable--has the advantage of densifying the surface and making it less absorptive of moisture. A good hard troweled surface on air entrained concrete is durable in freeze-thaw exposures by virtue of the fact that it does not absorb much water.