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Ask the Carpenter: Replacing urine-stained carpets

Ask the Expert Home Improvement
When a dog soils the carpet, the damage can be more than what you see on the surface.
When a dog soils the carpet, the damage can be more than what you see on the surface. Brennan Linsley/AP

Q. Our dog has soiled our carpet through to the floor boards. What should we do before we put down new carpet?

KAREN E. HARKINS

A. Dog urine is a made up of ammonia, nitrogen, uric acid, bacteria, and hormones. Uric acid contains crystals that are left behind even after the urine has dried. It is those crystals in the impregnated wood that will linger. High humidity days tend to activate these crystals, so they will come back to haunt you after the carpet is replaced.

Apply an enzymatic pet cleaner (like Nature’s Miracle) to the soiled areas and allow it to dry thoroughly for at least 24 hours. These cleaners contain special enzymes that convert organic waste materials such as urine and feces into carbon dioxide and water. They continue to eliminate the odors and waste materials even when dry. When you apply the enzymatic cleaners, do not oversaturate the wood or it will warp. Repeat this step if the odors remain after the initial application.

In some cases, it is impossible to get urine odors out of wood. The most foolproof approach is to cut out and replace the stained sections, treat the rest of the subfloor with a cleaner specially formulated for pet urine, and install new pading and carpet. If the subfloor is particle board, you definitely should replace it. If the subfloor is plywood or solid boards, an alternative is to seal the odor into the wood with a mildew-resistant oil-based primer like Kilz Complete or Zinsser B-I-N. But before you can paint anything, the subfloor must be completely dry.

Q. I’d like to remove old vinyl siding to uncover and repaint or restain the shingles below. My house was built in 1910. Neighbors tell me the exterior looked fine when a previous owner covered it with vinyl siding. It’s not bad-looking, and I’ve avoided some painting costs during the 10 years I’ve owned the house, but I prefer the look of well-painted shingles on old houses like mine. In any event, it’s time to repaint the trim and porches. There’s one wrinkle, though. Ten years ago I had cellulose blown into my exterior walls from the outside, so when the siding is removed, it will expose a few rows of regularly spaced holes now filled with styrofoam plugs.

When I ask contractors for quotes, should I ask for one for the painting as if the shingles were perfect, with an additional hourly fee for shingle replacement? It would bug me if I could see which shingles were the replacements after the house was painted. The originals are original to the house, as far as I know. Do contractors have access to old shingles?

MARK

A. You should have a carpenter replace the shingles as needed before painting. My only concern is that the roofing nails used to install the vinyl siding may have damaged the siding or at least introduced a ton of holes.

Contractors will not use old shingles. They’ll patch in with new. But don’t worry, once they are painted, they should look fine. I’d get a quotes from painters directly.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.