An owner's representative recently disapproved of cracks in concrete floors on steel decks and asked the contractor to correct them. The floors had been cast on a permeated corrugated steel deck supported by a structural steel frame. The contractor inquired of CONCRETE CONSTRUCTION whether there is a known way to prevent such cracking and a way to use control joints in such floors. Although a crack-free floor is always desirable, random cracks are to be expected in the kind of floor described. Any concrete floor cast on a metal frame and deck is severely constricted. While the concrete shrinks the steel frame does not, causing high tensile stresses in the concrete which ultimately lead to cracks. In places shrinkage may cause the concrete to ride up on the corrugations of the deck and add to the nonuniform conditions that contribute to cracking. For this reason control joints parallel to the corrugations will not be successful. Control joints are most effective in slabs which can slide on a smooth base as drying shrinkage progresses. Control joints running perpendicular to the corrugations can be spaced at intervals of 15 to 25 times the thickness of the concrete. The conventional way to take care of the cracks has been not to use control joints but to use shrinkage and temperature reinforcement to distribute cracks uniformly and hold them tightly closed. The minimum amount of steel needed can be determined from the ACI Building Code. Another possible solution is to place an unbonded topping on the structural floor.