Reviving the Glory of Old Wood Floors : Renovation: Careful sanding and a quality finish produce a strong, easy-to-clean surface.

It is a look that old-house lovers dream of: an expanse of gleaming, beautiful, bare wood floor.

Old houses were built with wood floors; sometimes the wood was covered with paint and linoleum, sometimes it was finished and covered with rugs.

In the past few decades, bare floors have been covered up when somebody got tired of taking care of them and when wall-to-wall carpet became both widely available and relatively inexpensive. Carpeting was also said to be “easy to maintain.”

Well, thanks to modern machines and finishes, the bare look is fairly easy to restore and extremely easy to maintain. Three coats of good-quality polyurethane provide a tough, durable finish that can be cleaned with a damp cloth.

Hardwood floors are the easiest to sand, but even soft-pine floors can be effectively sanded if they are relatively free of deep stains and major splinters.

Even with hardwood, it is unlikely you will achieve a perfect surface; old floors are going to look old. And if they are patched, or badly stained, the damage will show. A wood stain, carefully applied before the polyurethane, can help even out the finish.

But the real question about floor sanding is who’s going to do it?

Sanding floors is a dirty, noisy, dusty, smelly job that can put a serious crick in your back. If you are the owner of a strong back, it is a job you can probably do yourself. Prices for hiring professionals to do it for you vary widely around the country, so it may be worthwhile to get a couple of bids from experts before you tackle a weekend of sanding.

The machines that do the sanding--the drum sander and the edger--are widely available for rent at hardware, rent-all and home-improvement outlets. They are fairly simple to operate, though they are heavy and require a certain amount of finesse in their use if you want to avoid gouging the wood. Floor sanding is not a highly intellectual activity, but you need to keep your wits about you.

Partly because of the expense and partly because the floor will be so vulnerable, you need a clear block of time to finish the job. Polyurethane needs to dry between coats. It usually takes at least 12 hours; if humidity is high, it may take longer.

Whether you hire someone or do the job yourself, the procedure should be the same. Before sanding begins, the surface has to be relatively clean and free of obstacles. That means all the staples from the carpet padding have to be pulled up, all the nails from the carpet strips have to be removed, and other nails have to be recessed (use a nail-set and hammer) so the sandpaper won’t catch on them.

Most floors require three passes with the drum sander, using, in turn, coarse, medium and fine paper. Between each pass, the edger, loaded with the same grit of sandpaper, is used around the walls and in small areas where the drum sander won’t go.

Corners and extremely narrow spaces--under radiators, around pipes--will have to be hand-scraped and hand-sanded. Sometimes the edger leaves circular marks on the floor; those too should be hand-sanded (though sometimes a small electric hand-sander will work).

As a general rule, the coarse paper (and initial hand-scraping) should remove the old finish. If there’s finish left, finer grits will simply clog up. The medium and fine grits smooth out the wood.

Once the sanding, scraping and edging are done, the floor needs a thorough vacuuming to get rid of surface dust. Remember that a lot of dust will be in the air; you may have to vacuum several times as it settles.

Polyurethane should be applied with a brush; rollers leave an orange-peel surface that looks awful on the floor. Wear knee pads and use small landmarks, like switch plates and knots in the wood, to keep track of where each paint stroke ends. It’s easy to keep track while applying the first coat; the next two will be difficult.

The first two coats should be sanded very lightly when they are dry to even out tiny surface imperfections. We use a drywall pole sander; you can stand up and swiftly cover the whole floor.

Applying the finish is a somewhat tedious process (though it is a lot quieter than the sanding), but resist any temptation to skimp on quality of polyurethane or number of coats.

When the floor is done and you see the change in the room, your aching back will feel a lot better.

Distributed by the Los Angeles Times-Washington Post News Service.