Bleaching pet stains out of hardwood floors, before or after sanding?

Bleach Pet Stains

Q: We just purchased an old house that has dark pet stains on the hardwood floors. I have read several tips regarding bleaching pet stains out of hardwood floors and I am thinking that I should use the 50%-50% bleach and water to start. Should the floor be sanded first? The house is going to be used as a rental and we are trying to conserve money. Do you have any other suggestions?

A: The wood has to be exposed, free from finish for any bleach to have a chance to work. Personally, I doubt household bleach is strong enough to remove such stains. I would check out Lee Valley Tools to see if they have anything more appropriate.

Similar Q: Can I apply bleach more than 2 times on a hardwood floor? What happens to the hardwood floor if its bleached too many times?

A: I don’t know the answer because I’ve never had a reason to bleach more than once. If you have a scrap piece of wood why don’t you experiment with it and see if anything nasty happens… and then let me know.

(As of yet we haven’t received a follow-up!)

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?

New dark/black spots on my hardwood floors

Q: I’m noticing new dark/black spots on my hardwood floors. Should I be concerned? What causes this?

A: I can’t even give a comment. Is your floor wax finished or does it have a polyurethane top coat? Do you have pets who are using the floor as your toilet? Are these shoe scuffs? Do you use an appropriate cleaner? You haven’t given me any information, so I don’t know what to say.

Is there a product that will remove pet urine stains?

Q: Is there a product that will remove pet urine stains (black discolouration), which were found beneath carpet underlay? The floors are 51 year old oak hardwood, and large areas of the dining and living room are affected.

A: There are 2 component bleaches that would probably do the trick. Where to find them is any one’s guess. I haven’t used bleach in more than 20 years.

Related Q: In response to a question about using wood bleach to remove dark stains from oak flooring, you said you haven’t used that method in over 20 years. So what do you do to remove the stains?

A: I change the boards.

Related Q: You mention 2 component bleaches that might remove pet stains, but I don’t understand what you mean by this? Can you clarify? Would oxalic acid work?

A: The bleaches I used many years ago were composed of a gallon of part A and a gallon of part B. Extremely corrosive and would remove the red from red oak. Oxalic acid should work.

Stain and dark pet stains

Q: I am refinishing my 45 year old oak floors. When I removed the carpet there were 3 dark stains. I figure it is pet urine. Sanding is finished, but the stains are still visible. If I apply a darker (perhaps cherry oak) stain, will it hide the urine stains or will they just get darker? Could I apply less stain to the spots to try to even it all out?

A: I would think they will likely go darker and you may have to use a stain that is heading more towards black to hide them.

Similar Q: We recently bought a house which has manufactured light color, oak maybe, wood floors. They appear to have a layer of real hardwood on top and then about 3 layers of other type material. We have an old dog with control issues and his urine has stained the floor a darker color in spots. No bucking or other damage from the moister, but stained.

Can we stain the floor with a much darker stain like dark walnut or kona to cover/blend in with the stains and then put polyurethane on it? If so, do we need to hand sand the floor first?

A: Sorry for the delay. All existing finish and or stain has to be removed to clean wood and then stained. Going with a dark stain may or may not completely hide the pet stain. It should help to hide it. There are also tinted finishes but they really aren’t meant for floors. Perhaps if you have some extra boards you could just replace the ones damaged. This is an engineered floor.

Black stains on wood floors not fully sanding out

Q: We have discovered many black stains on wood floors after we pulled out the carpet. We tried to sand them out. While some got lighter, others did not. There seemed to be a smell of urine during the sanding, so I’m assuming that these stains may be from pets. Is there anyway to get these black stains out?

A: Your best option is to replace the damaged boards, which, if these pet stains are all over the place, would mean replacing the floor. Option 2 is to stain the floor dark enough to mask the spots. If odour is a concern, you could apply a barrier coating over the stain before applying the finish top coats. Such products as Zinsser Seal Coat or Dura Seal Universal Sealer are dewaxed shellac products that are excellent barrier coatings which dry very quickly and offer excellent adhesion.

Black stains did not come out when sanded

Q: I just had older Oak floors refinished. They are approximately 40 years old. There were black stains in the hall way that would not come out when sanded. We kept the floor stain the same as the original but the black stains look horrible. Would you suggest restaining the floors a darker color so the darker stains won’t show as much? We are in the process of fixing up this house to sell.

A: Your floors are probably 3/8″ thick, top to bottom and are good for 2, maybe 3 sandings. I think I would get your real estate agents opinion about colour. But keep in mind, this floor is thin to begin with. You either leave it as is, or remove/replace the stained areas and start over.

Pee peels

Q: My dog peed on our floor and we did not notice this until the next day. After cleaning up the mess, I noticed that the finish had lifted and peeled on one side of the wood slat. The wood in not discoloured but you can see where the finished has peeled. Can I try and apply polyurethane to that one spot or is it better to sand the whole slat and then apply polyurethane to the whole slat of wood?

A: You will likely have better results by doing the entire piece of wood. Make sure it’s dry first.

Re-dampening urine stains

Q: I have old urine stains on my hardwood floors. There is no odour or buckling, just dark marks. When the moisture is high these areas become damp. How do I stop this?

A: If I understand you, during high humidity these old pet stains become damp? I don’t have any clue why that would be. If you want to apply something over these spots to stop odour, I would suggest the Universal Sealer, which is shellac based and made by Zinsser.

Urine stains

Q: We have recently removed carpet from a house that I have lived in for 2 years. The carpet had been down for 10+ years and it was used by the previous owner’s dog as a bathroom. Under the carpet is hardwood, but is has urine stains. The carpet pad was stuck to the floor and some of the staples were rusted. Upon removing the pad and scrubbing the floor, there are light stains left by the mess. What do we need to do or use to restore the floor to the way it should be–pretty and unstained?

A: You may have to replace the floor to achieve a light colour. There is no way, short of sanding, to know if the stains can be removed. It doesn’t sound very hopeful.

Small pet stains on floating floor

Q: I found your web site while searching out how to manually try and fix several pet stains my dog has made on my hardwood floors. I have floating hardwoods that I believe were put in on top of a tile floor. Unfortunately the dog has had a couple of accidents in his old age. There are three none bigger than the palm of your hand. I don’t want to have to replace the floor if not absolutely necessary (I’m not sure I could even find replacement boards since the floor was put in prior to my owning the house). Is there anything I can do cleaning wise to try and pull the stain out of the wood? I did read on your site one of you visitors tried hydrogen peroxide and was able to bleach the stain out of their wood but I’m not sure if that will work for a pre-finished floating floor systems. Do you have any suggestions?

A: While I hear suggestions, I have not tried most of them. In most cases replacement of the boards is the best and easiest way to deal with the stains. Who makes your floor?

Hydrogen Peroxide to remove black stains

Q: I recently removed 30 year old carpet from hardwood floors. I discovered some spots that were dark black (I am guessing pet stains). I applied hydrogen peroxide to them and after a few treatments, the black stains lifted and the wood was left white. I chemically stripped a 3 X 1 rectangle around the white spots so that application of stain would be even and not spotty. My problem is that the white spots in the wood are now not taking the stain as dark as the chemically stripped areas. Is there anything I can do?

A: Hydrogen Peroxide to remove black stains? Never heard of that. I must try it out myself.

There is an old trick that helps achieve an even staining. Before applying the stain, wet the entire floor with water and let it dry. This will open the grain of the wood more and allow better stain penetration. Now you have already applied the stain. What you could try is to scrape or sand just those spots and once you have removed as much of the stain that is possible, wet the area and stain as above. Hopefully that will do the trick.

A few small stains

Q: We have a few small stains on our hardwood floor. They are either from water or from paint. Can we sand and recoat just those small spots, or would we have to do the whole floor?

A: You can try the less intrusive approach first, and just try to re do the spots. Better chance of getting a good blend if you try to finish entire boards, rather than simply part of a board, in which case you will no doubt see a lap line.

Pet stains and prevention

Q: I’m planning on re-finishing my hardwood floors after discovering black, and I mean black, pet stains. I’d had some boards replaced before for the same reason, and thought I solved the problem with the dog, but not so. I didn’t have the floor resanded and refinished, then, just boards being replaced after being taken from another room. Now I’m faced with a much bigger project. I found the Q & A on your site to be extremely helpful — thanks for setting it up the way you did. I couldn’t find the answer to these questions, though:

1. Assuming I replace pet-stained boards where needed and have the whole floor sanded and refinished, disregarding costs at the moment: Is there ANYthing that can be done to seal a floor so that future pet stains won’t penetrate and ruin it? I just don’t want to have to do that all over again. Or is that just not possible, even if done by a professional?

2. I was told by a local refinisher that the process is what amounts to a MAJOR disruption. This company will NOT remove furniture, but insists on having everything out of the rooms in advance. The company rep said some customers rent a storage truck, put their furniture in it, and park them in the yard. Storage, of course, is a separate, hefty expense. Then, everyone has to move out of the house for at least 3 days for all the sanding and refinishing, so the coats of finish will dry properly and won’t get walked on. Not all of my house has wood flooring, so this company will try (note “try”) to hang plastic so the dust is more or less contained and then cleaned up in the worked-on area. I read your warnings about do-it-yourselfer’s trying floor refinishing, and am more than pleased to let someone else do it. But considering the cost and hassle, I’ve got to ask: Is there any alternative AT ALL to this huge project? Okay, maybe I’m grasping at straws. At this point, I may have to just go to wood-patterned sheet vinyl, which I’m told is the only really pet-stain-resistant material, but I’d sure love to just re-do the floors. Once you stop laughing at my question, please send me any comments, suggestions, or instructions you may have to offer.

3. Assuming I get local professionals out to the house to do estimates: What questions do I need to ask them to make sure they know what they’re doing? (I know that requirements, maybe licensing may not be the same here in the US.) Is there anything I need to watch out for? Red flags that indicate I should run for cover and not shell out money?

Thank you so much for even offering to field questions. I’m glad I found you in a web search.

Knoxville, TN

A: You likely have restrictions in the U.S. regarding the use of oil based polyurethane, which I prefer to use. Such polyurethane offers excellent protection against moisture penetration of any kind if applied with at least 3 coats. I am not so sure that even hi end water based finishes offer such protection to moisture penetration.
If your floors are refinished with an oil/solvent based finish, make sure no sealers are used as a base coat, but only polyurethane, with each coat properly buffed to gain adhesion. Water base is a different approach. Ask what type and brand of finish will be used and check the product out on the Internet. The best water base finishes are those that require a cross linker, though there are a few good ones that don’t. Basic Coatings and bona Kemi both make good quality water based finishes.

For the past year I have been using a dust containment system (see my web site) which captures all the dust, and after using it, I can’t go back to the old ways. It is possible to totally seal the doors so dust stays in the work area. However, it is still all over the walls, sills etc. and will need to be cleaned up by the workers.

I would ask the guys you consider doing the work what their approach and procedure is. Be extremely cautious of companies that “low ball” their prices. If you feel the contractor has your interests at heart, and is really experienced in this line of work, then go for them.

I can understand why they will not move furniture. Floor finishers are not furniture movers. I work alone and can’t clear out a persons house. I am willing to assist in the job if they need me to. My current customer hired 3 guys to move their furniture including piano into other parts of the house. It took about an hour and was well worth whatever they may have paid. A previous customer went the trailer route with her furniture, which is really the better way to go, since it gets the job over and done with in one trip, rather than splitting it into smaller jobs, which will cost more in the end, and prolong the upset of moving furniture multiple times.

It is often the case that there is an area of the house that will still be available to the homeowner, such as kitchen, basement rec room etc. and if they wish to stay in those areas during the procedure, and have access that doesn’t require passage across the wet polyurethane, and can tolerate the smell (some people are very sensitive), then that is fine by me. Water based finishes don’t have a strong odour, and dry/cure much more rapidly than oil based finishes.

I don’t know if any of this has helped, but if your floors are well finished and you try and catch your pet when they have a mishap, there should be no problem maintaining the floors. Periodic, as needed, buff and recoats will keep the finish in good shape.

Finish has worn off the floor

Q: I recently removed my living room carpeting, as it was filled with pet stains. The hardwood floor underneath was for the most part in good shape. There are a few areas where the finish has come off the hardwood floor. The floor boards are in great shape, no warping and the floor cleaned up nicely. However I want to know if I can just refinish these areas of the floor if there are no deep stains or smells. Can I re-stain these areas of the floor without having to refinish the entire floor?

A: Is the floor actually stained a different colour? Are you saying the finish has pulled off these areas or it has worn off with time and exposed the wood? If this is the case, and the wood has become discolored and you want a nice job, it really should be sanded professionally from scratch. When properly done the floors should give you years of very good use, with the occasional refresher coat when it starts to show signs of wear or marking.

Reply: The finish has worn off the floor. The areas are down to the natural wood with absolutely no finish on them. The wood in these areas is in excellent condition and there is absolutely no odor in the wood from the pet stains. We are eventually thinking of having the floors refinished, but in the meantime I would like to know if I can refinish over these areas until we have the time and money to refinish the floors. I’m looking for a temporary fix until that time is feasible.

A: Brush several coats of finish over the spot, buffing lightly between coats. It will show, but at least it will protect the wood until you are ready to have them refinished.

Severe black spots

Q: We just pulled up our carpet, and there are severe (water) black spots on our wood floors.

A: It depends how extensive the damage is. If it is only one or two confined areas, you can change the boards with new. If it is extensive, you either have to replace the floor, or stain it very dark to try and hide the black. It is unlikely it will come out with a professional sander doing the work, but it is never possible to know for sure until the work is started.

Similar Q: My landlord is on my case about a large circular black “burn” (small baseball size) that is outside of my room door. Never noticed it before, looks like dark discolouration knot but spans into 3 pieces of wood slightly and seems to be under finish coat. Thoughts on what can cause this clean circular burn? Might it be a mistake from the sanders/finish coat floor workers? Thanks.

A: Black marks can be anything from water damage to fungus to tannin in the wood reacting with the solvents in the finish.

Pet urine stains

Q: We just purchased a home with hardwood floors throughout; however they all have dark brown stains. We do not know if it is from water damage or from pets; my husband think they are urine stains from the previous owners pets. We would love to keep the hardwood floors and are hoping that the stains can either be removed or be covered. Can you please tell us what we could do to save our floors? Can we stain them darker to hide the stains if we are unable to remove them?

A: I don’t know of any certain way to remove the stains. If the floor is stained dark, it should help to mask the marks.