Q.: I've had many recommendations on how to minimize curling of concrete floors--mostly recommendations about mix proportions, improving the possibility of moisture escaping from the bottom of the slab, and shortening the joint spacing. Would thicker slabs curl less?

A.: They certainly would. Robert Tobin, Regional Structural Engineer in the Los Angeles office of the Portland Cement Association, has developed a formula that describes curling. The amount of curling depends on the difference in shrinkage between the top and bottom, sc, the length of the slab, l, and the thickness, t: where Delta is the vertical movement of an end. Since the l term is squared, the length of the slab (distance between joints) is by far the most important factor.

The longer the distance the greater the curling. Thickness affects curling inversely; the greater the thickness the less the curling.