Q.: We re replacing concrete floors, pads, and pedestals damaged by hydrofluoric acid spills in an oil fuel processing plant. The acid is at ambient temperature and concentration varies from 10% to 60%. How do we protect the new concrete so it doesn't deteriorate?

A.: Bob Schoenberner of Schoen Industries, Inc., suggests that you use a vinyl ester material. Hydrofluoric acid attacks silica, so don't use a silica filler. The least expensive approach is a coating of carbon-filled vinyl ester. However, if the concrete cracks the coating will probably crack too and allow acid to penetrate. To prevent this problem, first put down a glass-fiber-reinforced asphalt membrane and then apply the coating over the membrane. Instead of using a coating, you can trowel on a l/4-inch-thick carbon-filled vinyl ester mortar over the asphalt membrane. This provides more protection but costs more than a coating. For severe exposure conditions you may need to cover the membrane with carbon bricks set in a vinyl ester mortar.