Q: A client asked me to install hardwood strip flooring in his carpeted living room. When I removed the carpet, the subflooring underneath was solid, but it was stained with dog urine. Can I just treat the stained areas or put down a layer of 15-lb. felt before installing the new flooring, or do I need to replace the subflooring?
A: Floor finisher Michael Purser, owner of the Rosebud Co., in Atlanta, responds: I once owned a 100-plus-year-old home with very nice pine floors. A previous owner had quartered his dog in a rear hall and, as you can imagine, there were urine stains. Since it was pine, the discoloration to the wood wasn’t too bad, so I just sanded and finished it with three coats of finish. However, on warm, moist days in the summer, moisture would collect on the surface of the finish. The amount of moisture was noticeable (I thought I had a roof leak) and eventually the finish started to fail. I ended up going back in and removing and replacing the flooring. Lesson learned!
Think about it: You have the floor open, you can see the damaged wood, and if you don’t replace it now, it will never be done. A carpet and pad can act like a sponge, holding the animal urine and letting it saturate the subfloor. Even if the subfloor seems solid, a lot of animal urine has probably soaked into it. I am not a chemist, but I do know that animal urea contains ammonium compounds. Aside from the odor, the salts in the ammonium will attract moisture—in the same way your salt shaker will develop beads of moisture in the humid summer months. If the subfloor is above a crawlspace or damp basement, you can bet on having a persistent moisture problem with the newly installed wood—which falls into the nightmare category. So I’d just yank out the stained subfloor and replace it.