How to fix hardwood floors discolored by pet urine

Q We have two rabbits in a cage indoors, and liquid spilled out and stained our wood floor. The dark areas are along the joints between boards and where ends of boards butt together. Is it possible to sand and refinish this portion of the floor, or must we redo the whole room?

Laurel

A Unfortunately, animal urine contains ammonia, which permanently changes the color of wood. Woodworkers sometimes use ammonia deliberately for just this purpose, in a process known as "fuming."

You may be able to sand and refinish the area, or you might need to replace that section of flooring. It depends on how deeply the wood is stained. If you're not very picky, start by getting a small container of oil-based wood filler (Color Putty is one brand) in a color that matches your floor as closely as possible. This kind of filler remains rather soft.

"You can push it in to seal and disguise the area," says Frank Kroupa, technical adviser for the National Wood Flooring Association, a trade group. "If you can't see the stains, this might be good enough."

If that doesn't work, you need a professional, one who repairs and refinishes wood floors. If your existing floor was factory-finished and you have replacement pieces, a pro can quickly remove the damaged boards and install new ones. If you don't have extra pieces or if you have flooring that was finished in place, you'll need to replace the damaged area with new boards stained and finished to match.

If the finish on surrounding pieces is fairly new, the patch might blend in even if you don't recoat the whole floor. the surrounding finish has dulled, a fresh coat throughout is the only way to get an even sheen. Even then, though, you probably won't need to sand the whole floor down to bare wood.

Costs might range from $100 to $1,000, which would cover replacing boards in an area about three feet square, Kroupa said.

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