Q: We have an outdoor wood deck facing the water, which serves as a carport roof. We were advised to use tongue-and-groove fir; however, rain and snow still come through the boards, rotting them. (The rest of the deck planks are spaced a half-inch apart). Every year we scrape and paint the tongue-and-groove boards with latex, but this year we had to replace so many of them that we sanded the entire deck and stained it. Now it seems the stain is not enough protection either - the wood is drying, darkening and splintering. Would you advise more stain, or a varnish or shellac seal?

A: As you have discovered, tongue-and-groove boards are a poor choice for a wood deck, and rot is almost inevitable. A wood preservative or paint would help, but only if it was applied to both sides, and to the more vulnerable edges. I advise your continuing use of a stain, but use one that has a preservative added. In the long run, you should plan to rebuild the deck with 2-inch spaced planks to permit water to run through. Unfortunately, you will have to find some other way to provide a watertight roof over your carport.

Q: About a year ago I painted my basement floor with floor enamel. It dried quickly and looked great, but it is now chipping. Should I have painted the floor with some other kind of product first?

A: Not unless it was recommended on the label. As a rule, most deck enamel and floor paints need no special primer; you simply apply two coats of the same product. The chipping could be due to poor adhesion because wax, dirt, dust or other foreign matter was not removed, or because you applied one thick coat instead of two thin ones.

Questions about home repair problems should be addressed to Home Improvement Department, The New Times, New York, N.Y. 10036. Only questions of general interest can be answered in this column.