Q. Seventeen years ago we tiled our large dry basement floor with asphalt. Five years ago it began to curl. A white powdery substance appeared under the tile. What is the cause and remedy? Betty B. Herter Warren, N.J.
A. Remove the old tile and mastic with a propane torch and putty knife. Clean the floor with a solvent that is recommended by an asphalt-tile manufacturer or a local dealer.
Seal the cleaned floor with Seal Glaze by Sealwall Products Inc. or equal -- a clear acrylic material that is absorbed into the concrete pores and dries to a finish with a slight glaze. Seal Glaze prevents the dusting of concrete through the carpeting.
Alternatively, if the substrate is suitable, you could apply a rubber-based enamel paint which "breathes," allowing the moisture to come through.
You also could install a resilient flooring after the old stuff is removed. Ask your local floor dealer to suggest a product -- and especially the kind of mastic to use.
The white powdery substance which you see on the floor only indicates that there is moisture in the slab. The moisture, of course, caused the old tile to curl.