Over a period of four years, A. H. Gustaferro, seminar chairman for the World of Concrete, has collected more than 200 technical questions from registrants, mostly from individuals who are dealing with concrete floor construction and its problems in the field. This article contains some of these questions and their answers. Most of them were selected either because they represent a broad general interest or because they resolve a somewhat unusual problem. Questions have been classified as follows: concrete mixes, jointing, reinforcement, cracking and crack prevention; finishing, toppings and two-course floors, vacuum dewatering, curing, cold storage floors, surface problems, deterioration and protection, and repairing.

Q: On floors to be subject to fork-lift traffic, should control joints be formed by hand or sawed? A. Hand-formed joints generally don't last long under fork-lift traffic. Sawed joints work better. These should be filled with epoxy sealants.

Q. When you receive concrete containing little or no coarse aggregate with the sand, what is the best method of preventing cracking? A. First, every effort should be made to see that concrete with an adequate amount of coarse aggregate is supplied. If this is the only concrete available, however, we would suggest two ways of overcoming the difficulty. One, reduce the joint spacing to about 8 to 10 feet on centers, and two, use welded wire fabric in the floor. The cross sectional area of the mesh should be no less than 0.1 percent of the cross sectional area of the floor, for example, 0.072 square inch per foot for a 6-inch-thick floor. If steel mesh is used it should either not cross the joints or the joints should be deep enough to cut through the steel mesh.