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Q.Recently, I removed wall-to-wall carpeting from an older maple floor finished with (I presume) polyurethane. While the finish had some paint splatters and stains, the flooring itself looked to be in good shape, so I simply scuff-sanded it with a pole sander, scraping and hand-sanding the tougher spots. Then I vacuumed the floor, wiped it down with mineral spirits, and applied a new coat of polyurethane. This was a process I had used in another room of the house with good results, but in this case the polyurethane has started to flake and peel away, particularly in high-traffic areas. What happened? Is a full refinishing the only option at this point?

A.Michael Purser, a second-generation wood-flooring contractor in Atlanta, responds: There are a lot of reasons a floor finish might not bond during a recoat. But based on your comments about the carpeting and your description of the area where the delaminating of the coating is occurring (in high-traffic regions), I am willing to put good money on the likelihood that some type of contaminant — probably paste or acrylic wax — was on the floor. This would have been a natural alternative for the previous owner to have chosen for a high-traffic area to restore the luster before giving up and going to carpeting. The reason the finish you applied is delaminating now is that it cannot properly bond to the old finish.

Unfortunately, waxes of any type are very difficult to detect without some knowledge of what to look for or how to test for their presence. For example, rubbing a cloth dampened with mineral spirits onto a section of flooring is one method I use to find paste wax. To find acrylic waxes, I'll use either alcohol or a mild ammonia solution, both of which will slightly discolor an acrylic finish.

The problem, however, is that neither paste nor acrylic wax can be chemically removed with 100 percent certainty. Mineral spirits simply dissolve and redistribute paste waxes over a larger area, and have no effect at all on acrylic waxes, which can't be removed with alcohol or ammonia, either. Because the results can be so uncertain in the presence of contamination, every manufacturer of wood-floor coatings tells you not to apply its products over a finish that has been previously waxed.

If you're considering recoating a floor, I strongly recommend that you get in touch with a wood-flooring contractor. This person will usually know what to look for and will be able to perform some simple tests to determine whether there are any surface contaminants; he or she can also tell you which coatings can safely be applied to which finishes.

Meanwhile, I'm afraid you are faced with a full sanding and refinishing if you want a coating to go down and stay down.