In the absence of specific instructions, what would be a safe set of rules to follow in respect to the amount of cover to provide for reinforcing steel?
Exposure must be taken into account. Some specifications call for at least 3/4 inch of cover for slabs and walls not exposed to the ground or to the elements. Cover should be not less than 2 inches for bars more than 5/8 inch in diameter, or 1 1/2 inches for bars 5/8 inch or less in diameter, when the concrete is exposed to the weather or the ground. The thickness of concrete over reinforcing should always at least equal the diameter of the largest round bars. All reinforcement in columns should have at least 1 1/2 inches of cover, and the same cover should be provided on the bottom and sides of beams and girders.