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Q.What is a good, durable, transparent finish for a bare radiant slab? I’ve tried Glitsa over colored concrete. The finish looked great initially, but was not water-resistant. A year later, there was a fair amount of delamination and flaking. How should I refinish the floor? Would a polyurethane finish bond better? Also, for the future, should new concrete be acid-washed before applying a coating?

A.Ed McPartland, a Wellfleet, Mass., builder, replies: Glitsa is a catalyzed varnish designed for wood floors, so it’s not surprising that it didn’t work well on concrete. To remove it, apply a chemical paint stripper, cover it with wax paper for about 15 minutes to prevent drying, then suck it up with a wet vac. Be very thorough with this process. Get down on your hands and knees and eyeball the floor with the aid of a strong light, to pick up any remnant "flash." Make sure the concrete is completely sponge-clean and dry before refinishing.

I don’t use urethane because it doesn’t hold up to wear. I have acid-washed concrete in the past but haven’t been satisfied with the result, and I don’t think it’s absolutely necessary.

I recommend finishing the slab with Butcher’s Wax. The finish looks great, goes on easy, repels water, and is easy to maintain and renew. Apply the wax with a rag or other recommended applicator.

If you really want a urethane-type finish on the floor, you might consider a clear epoxy. I occasionally use a Sherwin-Williams two-part catalyzed epoxy. It provides a good finish, but scratches tend to show. To minimize this effect, you can apply satin urethane over the epoxy, first sanding the epoxy lightly to provide "tooth" for the urethane bond. Be forewarned that epoxy is extremely difficult to remove if you change your mind.

You might also consider an acrylic sealer. A local colleague uses this product for the concrete countertops he makes and finds it provides a satisfactory finish and is fairly easy to renew.