Slab-on-grade curling can be a big problem, especially when the slab must be covered by wood flooring. That's why curling--not flatness--was the major concern of the wood flooring installer for the new gymnasium at Elmira College. On this project potential curing problems were addressed before slab construction began. This careful planning, facilitated by the cooperation of all the parties involved, resulted in a high-quality slab on grade that made an excellent base for the wood floor.
Curling occurs when the top of a slab on grade dries and shrinks faster than the bottom. The differential shrinkage causes slab edges to rise at joints. The following design elements were included in the specifications: monolithic slab construction to eliminate all joints and a reinforcing mat of #4 bars; thickened slab edges to add ballast; the use of a continuous moisture barrier under a dry slab subbase and a prolonged wet cure of the slab concrete.
Although this project's nontraditional slab design required extra reinforcing steel and a larger work crew to handle the continuous concreting operation, any additional construction costs were balanced by cost savings in other areas.