Q: My dog is wearing off the finish on my solid hardwood floor. The flooring was installed in the 1920s and was sanded once and stained more than 20 years ago. It remains in good shape except for spots where the finish has been worn off and it's down to light wood. Can I repair these worn spots without having to tackle an entire room?

Ossining, N.Y.

A: It’s fairly easy to restore the finish on a hardwood floor when only the clear finish itself is dull or scratched. You or someone you hire would need to clean the floor, scuff up the old finish (typically with a buffing machine outfitted with a sanding screen, which is like fine sandpaper but with a clog-resistant mesh texture) and apply a new coat or two of finish.

Or, you could re-coat that worn finish using a product such as Rust-Oleum Wood Floor Transformations Kit, which includes a prep product that softens the old finish, enabling the new layer to stick without having to scuff up the floor first. Products such as these were developed because some of the floor finishes used today are so hard they can’t be screened or sanded to allow refinishing, though that probably won’t be an issue with your 20-year-old floor finish. (A kit with enough prep material and finish for a 15-by-15 foot floor costs $69.97 at Home Depot.)

Adding a new coat of finish won’t restore color to areas that have been scratched down to fresh wood. It’s possible to touch up a few scratches by applying stain with a narrow artist’s brush or a cotton swab, or by using a marker matched to the stain color. But the picture you sent shows a worn area much too big for that.

“Have a contractor come in and take a look,” suggested Rusty Swindoll, technical adviser for the National Wood Flooring Association (800-422-4556; nwfa.org). In all likelihood, a pro will tell you the entire floor should be sanded down to bare wood and refinished, Swindoll said. “But I wouldn’t give up on a floor without taking a look.”

If your floor has only one or two worn patches, such as what’s in the picture, a pro might be able to spot-treat it, especially if you make it clear you’re willing to wind up with some variation in the color and the sheen.

You may be able to do it yourself, subject to the same caveats. You would need to sand off the old stain and apply new stain in the area you want to repair. Identify the damaged boards, mask off surrounding boards with painter’s tape, and sand the damaged boards in the direction of the wood grain, using a sanding block or a piece of medium-to-fine-grit sandpaper wrapped around a piece of wood. Another option is to use a power sander on the worn area and then use a sharp hand scraper to remove the finish and stain from narrow fingers of wood that extend lengthwise into the boards beyond the worn area, which helps the new stain blend in better. (See “Blending a Stained Wood Floor” at woodfloorbusiness.com.)

Typically, you would need to sand or scrape enough to remove all of the stain color, because otherwise you’d risk winding up with a blotchy look when you apply new stain. But the stain on your floor looks so dark that it’s almost an opaque black. You may just need to sand until the lighter strips are evenly light, without worrying about sanding down the thin black lines where the stain seeped into the wood’s pores.

To get a stain color that matches, try sanding down to bare wood in a hidden area, such as a closet. But for testing whether you have sanded the worn area sufficiently, you will need to do another test on that section of the floor. Start with a very small area. Once you are satisfied, proceed to spreading stain over the entire area you sanded.

Use oil-based stain, and apply it with a brush or a rag. Have mineral spirits and a supply of cotton rags handy for wiping off excess stain, and wear nitrile gloves, which stand up to the solvents in oil stain better than latex gloves do. (Because you’ll be working with oil-based materials, extinguish flames first and ensure good ventilation. When you’re done, hang the rags separately to dry or spread them on the ground in a single layer; don’t leave them in a pile because of the risk of spontaneous combustion. Once they are dry, you can put them in the trash on collection day.)

Wait at least 24 hours for the stain on the floor to dry before you apply a couple of coats of polyurethane suitable for floors over the treated area. The patch will probably look shinier than the rest of the floor at first, but your dog should take care of that in short order.

Sometime soon after, consider having the entire floor screened and re-coated with clear finish. Or, if your patch is too noticeable, you can get a pro to sand and refinish it. Trying to spot-refinish first won’t be any more expensive than if you opted to do that initially. So there’s little risk in trying, provided you don’t sand too deeply into the floor.

There’s no guarantee about how many times a hardwood floor can be sanded and refinished before the wood wears down so much that the edges of the boards start to splinter and the sanding reveals previously hidden nail heads. It depends on how aggressively previous refinishers sanded. But a traditional hardwood floor, such as yours, can probably endure three or four more sandings, Swindoll said.

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