Can I save old dog peed on wood floors?

[John Morgan]

I bought an old house “as is” with nasty dog peed on wood floors. Has anyone had any luck salvaging old wood floors that are stained with dog pee and smell like dogs? I’m just trying to do a cheap rehab and want to rent it out soon. And want the dog smell out of this place. It’ smells terrible!

[Jim K.]

Originally posted by @John Morgan:

@John Teachout

Sub floor. It’s pier and beam. I was hoping there was an economical way to save the floors and just have them sanded down then stained. But wasn’t sure if all the dog pee over the years ruined the floors.

I've got you, John. Here we go.

There are three ways to work on pet urine dark spots on a wood floor after you sand it, wood bleach kits, oxalic acid, and peroxide. The most popular wood flooring far and away is oak, and that's bad news for you, because oak is the least forgiving to work with. Dog urine isn't as bad as cat urine, so it isn't all bad news.

Typically on oak flooring, the wood bleach kits (the most popular one is made by Zinsser) will lighten up the spot too much and look artificial. The oxalic acid (and get the 100% stuff on Amazon, not Bar Keeper's Friend) will get it just about right. Typically peroxide guys swear by hair bleach cream developer, because it can really do a range of lightening well, but it take times to develop skill in that.

After you lighten up the spot, you're going to have to seal and poly the wood. This will go easier with water-based than with oil-based poly. With water-based poly, you put on a coat of the stuff, and usually you're fine. With oil-based poly, typically application is to begin by adding a THINNED coat of the poly as a sealer, usually diluted 50/50 with mineral spirits.

Sadly, this will screw you very quickly, as the mineral spirits in the sealer coat will penetrate the wood deeply and bring out the spot yet again.

 So what you need to do is break out a spray can of clear shellac. This takes a long time to do right, but with practice, you can add 2-3 very thin coats of shellac over the spot without causing the treated wood to re-darken. After you get the spot and a 1-inch perimeter around it coated with the shellac, you can cover the whole thing with oil-based poly.

It takes a lot of practice to get this right, and it can get frustrating. But if you have the time to invest learning this trick well, you can bring back a lot of floors. A lot of flooring guys hate this because its a timeater. But sometimes they can fix a spot on the first shot, which makes them look good. If you plan to continue working in houses like this, yes, it's worth developing this skill.

Look online for how to use oxalic acid and peroxide cream developer to lighten floors, the actual technique you'll use. But a Zinsser wood bleach kit and follow the directions.

Sometimes, you're going to want the whole wood floor to be darker, and anytime you do, that's great news for spot treatment, because it makes matching the stained wood to the rest of the floor a lot easier. But other than giving oak the amber tint that tough, oil-based poly imparts, I've always been a fan of keeping old floors as light as possible when refinishing. Historically, of course, dark-stained flooring was less a fashionable possibility and more a solution used to hide multiple imperfections in cheap oak floors. When faced with an ugly situation where there are spots all over the place, however, it makes more sense to do a darker stain over the whole oak floor and make your life easier.