Q: We placed the concrete for post-tensioned decks for a three-story health club. The specified tolerance for flatness was 1/8 inch in 10 feet. A racquetball court will be placed on wood sleepers spaced 8 inches apart on the floor, but we've found that the surface is out of spec. There are some high spots, up to 1/4 inch, and some low spots that we've been asked to correct before they build the wood subfloor. What's the best way to do this?
A.: We suggest calling in a floor grinding specialist and working on cutting down the high spots instead of filling the low spots. You'll need to mark the high spots and check the elevation periodically as the grinding progresses. To get the names of grinding contractors in your area, call the International Grooving & Grinding Association at 704-684-1989. Once you've ground down the high spots, workers may be able to shim the low spots. Filling the low spots with a self-leveling underlayment is a possible solution, but isn't likely to work if wood sleepers will be fixed to the floor with powder-actuated fasteners.