Why do pet stains reappear?

Q: Some friends of ours had their hardwood floors refinished by professionals. The floor looked perfect after sanding, before the finish, but after the finish was applied, dark pet spots appeared. Why do pet stains reappear?

I am refinishing my floors and don’t want the same to happen. My sanding is complete and floors look good now, but is there the chance that the same will happen? Or was something done incorrectly to cause this to happen to our friends floor?

A: There is no way “pet stains” can be sanded away and disappear, then re-appear. (See update at bottom!) They are either gone or they aren’t. If they aren’t, you will see them on the freshly sanded wood. Perhaps these black marks are the result of “tannin pull”. Occasionally a floor, particularly white oak, can have high levels of tannin which can react with the floor finish and leave black marks. I’ve only seen it a handful of times in 34 years.

Follow-up Q: I was wondering if you could give some advice on what type of Semi Gloss Oil Based Polyurethane to purchase to finish my floors. I am a do it yourselfer, but am very particular and like perfection. The selection in our area is limited to these brands; Minwax Super Fast Dry Poly for Floors, Varathane, Valspar, Parks Pro Finisher, Zipguard. I have an extreme amount of time in preparing these floors (approx 600 sq. ft., including hallways closets and 3 rooms). I would like something that is user friendly (not catalyst, hardneners, etc.) because of my inexperience. Someone recommended that I go after the Circa 1850 Fast Dry Poly (bowling alley finish), and I have found some that can be shipped to me. It looks to be fairly simple… no sealers, etc. I have noticed that you have a real good word for the Poloplaz products, but I was afraid when I looked into it as it requires a sealer, then a gloss, then a finish coat. I am afraid of mail ordering all of these different ingredients, then running low of something right in the middle of the process, then having to mail order more. Considering your experience, is there any direction of product that you could steer me that you feel would fit my needs?

A: I’ve used Circa for a number of years. It is a decent oil modified poly. However, Poloplaz Primero is better, which is the reason I switched. It shouldn’t be too hard to calculate the number of gallons you will need. This coats are always best, and most of these finishes call for a spread rate of sq. ft. per gallon. It is not written in stone that you have to use the Poloplaz Fast Dry Sealer with Primero. It is just a better way to go. It has 37% solids compared to about 40% for Circa. Yet it penetrates much better to a smooth, even seal coat, and it does so in 2-3 hours. Circa would take overnight.

After that sealer is dry, you can coat with a gloss Primero (recommended), then when dry (overnight) buff well and apply the sheen of choice. If you have less than 500 sq. ft. you will need a gallon of each.

As a side note: Circa “fast dry” is, in my view, a mis nomer! There is no way this finish will dry for recoat any sooner than overnight. The claim of fast dry, I believe, is based on the idea of a dry brush coat on a vertical surface.

Send an email to billj (AT) poloplaz (DOT) com and tell him I sent you. They also have a waterborne with built in cross linker called 202 which I’ve heard good reports about. They have sent me 4 gallons to try out. I’ve heard it dries fairly fast and hard. Possibly not quite as hard as Primero, but it would cure faster, if you would feel comfortable working with a waterborne. Best application method for that is T bar or possibly roller.

Webmaster update: I recall a job a couple years ago challenged this perception. Stains were being continuously fed by condensation/water seepage. Pet stains were stinking to high heavens that should have dried out long ago. So one thing to look at is, what is below / around this reappearing stain? Is there anything that would keep reinvigorating it?

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