Mold worries after leaky toilet

Q: I had a master bedroom toilet leak and it caused a lot of damage to the carpets, door jams, baseboards, etc. It also got under my expensive, hand scraped hickory (4 years old) installed engineered wood floors. They are glued down on a concrete slab. The water damage experts said that there was still moisture under wood floors in the hallway and part of the living room. The floors show no signs of buckling or color distortion. My contractor said the installer did a great job installing them.

I am concerned about mold. Do you think I need to rip up the flooring and install new flooring? Or, if left undisturbed, are they okay as is? Will the concrete eventually dry out? I was told that if they are left undisturbed, mold will not cause health issues. Once it is disturbed by ripping up boards, then the mold can become airborne and can cause major health issues. Is this true?

A: If this was a floor installed on a raised sub floor then I would recommend ripping everything out because a large amount of water can seep and stay under there for a long time and take quite a long time to dry out. In your case, the floor is installed directly on the concrete with no space. I think the amount of water under there is minuscule and will transfer through the structure and evaporate. Keep in mind most needs a certain environment to grow. That would be warm and moist. If you have gone through this with no apparent damage to your hand scraped hickory, I’d sit down and enjoy a pint or glass of wine in my favorite chair and breath a sigh of relief.

Poly lifting where dog peed on floor

Q: We have a satin finish on out oak floors installed 2 years ago. Recently my dog peed a puddle and it sat for maybe 3 hours before we soaked it up. Was not yellow pee she just can’t hold her water long anymore – now that it’s up. The seams in the poly have lifted and it is not smooth any more to the touch. Is this normal? I spoke to my sister who has 2 dogs and lots of accidents on her satin poly finish and she said it just beads up and floor is fine. Even when she does not see for a full day? Thank you in advance.

A: If any liquid sits in the middle of a board coated with polyurethane it will bead up, yes. However, it can still find a way below the surface along board edges and it sounds like this is what has happened with you. If these episodes become more common the uric acid will eventually start to degrade your floor finish.

Similar Q: My dog peed on my wood floor. It hasn’t stained but the boards are swollen and slightly lifted where she’s gone. Can this be fixed or does my entire floor need replacing?

A: I would leave it for now and see what it is going to do. Maybe it will settle down when it dries out. At worst a board can be changed.

Main level floor affected by basement flooding

Q: In August we had some water in the basement. The temperatures outside were outrageous, high 30’s with humidity in the 40’s. Once the water was abated the Insurance company aggressively dried the basement. There were 3-4 dehumidifiers and about 10-11 large fans. Immediately after the fans and dehumidifiers were removed I noticed that my engineered hardwood floors on my MAIN floor were starting to sound like dry timbers. It has only become worse over the past couple of months so I am not at all confident that it will “reverse” itself like I was told may or may not happen. The floors were only put in 3 years ago and this is a real P*@@off! Could this very well be from the amount of equipment used to dry out the basement? The kitchen is right off from the basement and it somewhat open concept. The kitchen opens to the dining room which is open concept to the living room, which is where the majority of the floor issues are. Thanks.

A: I have a few questions: exactly how much water did you get in your basement? What is the flooring down there? Do you have a raised sub floor? Is the engineered flooring glued or nailed down? Have you noticed any humps, gaps between boards or cupping where the edges of the boards are raised?

Follow-up Q: The basement had an even 4 inches of water throughout. All the laminate was ripped out. But the damage and my questions are regarding my main floor. After the drying of the basement, we noticed the main floor; engineered hardwood nailed down with high grade underlay, started to make cracking sounds when walking on it. Even the drywall coming up from the basement cracked from being dried out so aggressively.

A: Well having that volume of water being absorbed by the surrounding structure you will get expansion. Then as it dries out or equalizes there will be shrinkage. The nails or cleats used to secure your engineered floor don’t expand however. They may pull or stretch a tiny amount but after everything dries out you floor will not be as tight as it was before. The less gradual a round of this expanding and contracting is, the more severe will be the results. During this process, I think it may have been wise for the insurance contractor to be monitoring everything with a moisture meter.

Similar Q: I had my floors refinished on the main floor. Two weeks later the water heater in the basement flooded. A couple days after the flood, the hardwood flooring above the water heater area ruptured and cupped. Is this due to the moisture from the water heater flooding from below in the same area?

A: I would think it is caused by that. How long did it take to clean up the flood? This is unfortunate. The only thing to do with these cupped floors is to give them time to stabilize. Hopefully they might flatten out on their own. It would be a good idea to have a dehumidifier running in the basement until all moisture is removed. If you have a hygrometer in the area it will tell you what the relative humidity in the area is.

Follow-up Q: Thank you for your response. The dehumidifier took about 2 weeks to get all the water out of the carpet in the basement. That’s why I think the upstairs floors ruptured and cupped. On my house insurance, I’m having issues proving to them that my hardwood floors were damaged and affected by the moisture caused by the flooding in the basement and they require proof in order to include the upstairs floors that is cupped and damaged above the flooded area. What proof can I provide to the insurance company that the upstairs flooring was damaged due to the flooded floors in the basement?

A: Contact the National Wood Flooring Association. They have inspectors fully trained who will come to your house for an inspection and write up a report. A number of years ago I was installing oak flooring on a main floor of a very old house and I found out that they were having a new concrete floor poured in the basement while I was installing this hardwood. I was very concerned about the volume of moisture that would be hitting the subfloor I was installing the oak onto. They stapled plastic sheeting to the bottom edge of the floor joists in the basement before pouring the cement.

Water softener overflowed onto laminate floors

Q: My water softener overflowed 26 gallons of water onto our laminate floors. We cleaned up the water and ran a dehumidifier and fans. The flooring covers about 800 square feet of our downstairs. However, the water ran under the laminate and when we took the vent covers off of our floor and felt underneath it was still wet, and that’s across the room. The flooring is resilient grip strip plank. There appears to be no damage to the floor above but we don’t want mold growing under the floor. Will the water dry up on it’s own with a dehumidifier or do we need to replace the whole floor?

A: Can you take the floor up without damaging it and keeping each piece in order? It will have to come up or it will take a very long time to dry out the area under it and you will end up with mold. That is quite a bit of water and it has to go some place. The way it is now, it is mostly locked in under that floor.

Can a roof leak cause cupping in a hardwood floor?

Q: Hello, is it possible for a roof leak to cause cupping? For the water to go down through the walls and get under the floors? We have cupping floors and that is the only possibility for water damage. Thanks!

A: Yes it is very possible. I’ve seen that happen more than once. All I can suggest is locate and fix the leak and run a dehumidifier to dry out the floors. Once in a while they will actually flatten out. Unless you suspect a lot of water under the floor the best thing to do is leave it alone and let it dry out completely.

Follow-up Q: Thanks so much for you response. Do you have a suggestion for how often and how long to run a de-humidifier without over doing it? Thanks!

A: I don’t think you can over do it running a dehumidifier. Having a hygrometer in the home can be helpful. It gives a reading of temperature and RH in the room. This time of year an RH of 45-50 is normal. I installed unfinished oak once in a very old house in Toronto. This place was on the edge of a ravine, surrounded by trees. One day it was mid 90’s and the humidity level was over 90%. In a panic I told the home owner, who wasn’t living in the house yet, to bring a dehumidifier fast before it started raining inside the house, lol. I wouldn’t expect you to have a moisture meter but if you had one you place it on the floor and it will tell you the moisture content of the wood. 6-10% if fine. 15 and up is not good.

Humidifier flooded floor

Q: We left a humidifier running for 8 hours overnight and in the morning the laminate wood floors were soaked. We cleaned up all the water and there appears to be no damage. Should I still use a de-humidifier to dry it up?

A: If you had a pinless moisture meter to check the floor directly that would help but I know that is unlikely. It wouldn’t hurt to run a dehumidifier for a day and see how much moisture is captured. It is positive that there is no apparent damage at this point as I would expect the cheaper products to have curled edges soon after getting soaked. Some of the good laminates such as Torly’s claim water can be across the seam of at least some of their floors for 5 days without any water penetration into the product.

Temporary water leak and mold

Q: Last night my humidifier leaked a few cups of water onto the wood floor of my daughter’s bedroom. We discovered the leak maybe 20 minutes after it had started and we cleaned it up, but this morning I found a little puddle of water in my basement directly below where the humidifier had spilled. Is it possible the water went through the floor and the ceiling into the basement? What’s the best way to make sure the floor dries and doesn’t mold? Thank you!

A: Clearly that is what happened and it actually is a good thing. The water ran right through rather than pooling and soaking into the board edges. I wouldn’t worry about mold. It requires a constant moist, warm environment to thrive.

Follow-up: That’s such a relief, thank you so much for your quick response! I live in Seattle so mold is always a problem. I’m glad my floor won’t be damaged. Thanks so much again, I feel much better!

A: I’m guessing you are in an older home that perhaps has individual planks of pine for example as a sub floor? I’m guessing that because the water seems for the most part to have leaked right past the sub floor into the basement. If you had plywood subfloor for example (which is a good surface to work with) the water would have soaked that and it would have had to evaporate through the floor to finally dry. So, given the small amount of water, that it didn’t pool and you got right on it…I doubt you will even have any cupping of the floor. Even if you do, I’ve seen it flatten after. If you had an ongoing leak over a long period of time you might have a mold issue then. Not in this case.

Related Q: Our laundry room pipes burst in the cold and flooded down into our kitchen. The wood was sealed with two coats of stain and three coats of varathane, but the water sat for several hours and has gone through the cracks. The boards are now curved up at the edges in a concave shape.

We have been running 2 dehumidifiers, but it’s cold and water isn’t coming out. We have a gas fireplace and it’s running strong. I am worried about making sure the subfloor doesn’t get moldy. Thoughts? We think we can sand down and refinish the floor. Thank you!

A: For mold to be a problem, alive and growing it needs a constant environment of moist warm air. If the floor is installed on plywood that likely means it didn’t seep into the basement so it is sitting on the plywood surface and underside of your hardwood floor. Without actually removing the damaged section of flooring it could take some weeks to thoroughly dry everything out and you wouldn’t want to sand the floor until that happens. You will need a moisture meter for wood to keep checking until you get readings 7-9% or at least close to that.

Similar Q: Our window AC unit leaked water inside and onto our carpeting/OSB subfloor. We dried carpeting, ripped out padding and are drying subfloor with fans/dehumidifier. Subfloor doesn’t look bad at all. However, there is water damage on ceiling below from leak. Do we need to replace subfloor? Clearly it leaked through. What is likelihood of mold developing in between subfloor and ceiling?

A: You aren’t talking about a huge amount of water trapped which will take months to dry out. Mold needs a certain constant environment to grow and thrive. Constant warm, damp or wet environment. I wouldn’t worry about it. Just make sure everything is really dry before doing any painting or putting your carpet back.

Similar Q: Our refrigerator leaked for quite a while before we noticed the floor in front bowing. We have real Brazilian cherry floors. The floor man said to let it dry thoroughly and then he will lightly sand and then refinish. We live in South Carolina where it is hot and humid, I’m afraid that the sub-floor will be moldy.

A: Under the circumstances It may be wise to remove the damaged area and let everything dry out. I assume this is factory finished flooring. Jatoba does change colour rapidly with light exposure so expect to see a difference between the old and new wood which should change rather quickly.

Christmas tree stand leaked

Q: I just removed my Christmas tree and found out the Christmas tree stand leaked and caused swelling along a seam in my 3/4″ engineered hardwood plank. Is there anything I can do to make the swelled boards go back to their original state?

A: Just leave it alone, exposed to air and heat. Hopefully as it dries it will shrink. It might leave a small gap which can be filled with colour match filler sold in tubes and jars.

Saltwater tank damaged floor

Q: My boyfriend had a saltwater tank (top-up) in the room above his large marine fish tank, for over a decade. The pine wood floor boards underneath this top-up tank were covered by carpet only. Now that the top-up tank and carpet has been removed, the pine floor boards are stained and constantly damp to the touch. The pattern of this staining and dampness seems to be only in the area of the top-up tank and is worse at the edges of the floor boards with islands of little or no damage at the centre of the boards. Could this damage be due to years of low level salt water spillage and therefore salt build-up in the wood, with the salt in the wood now absorbing moisture from air in the room making the floor boards constantly damp? What should we do about this flooring? I would appreciate your thoughts, we are a little baffled.

A: Wood normally absorbs air moisture and releases it. It sounds like there has been long standing leaking in this area with the water seeping between the boards. The sub floor may be soaked. I would love to put a moisture meter on the area. I bet it blows off the scale. Probably the best thing you can do is remove the section carefully. This will allow the structure beneath the floor to dry. It will also allow the pine to dry. If it isn’t too badly stained or damaged, you may elect to put the pine back in place when you know everything is dry. Or replace with new, but it will be impossible to get a colour match.

Related Q: Hello! Found your website on a google search. We came home to our 75 gallon fish tank leaking. It was about half way empty, so we are assuming around 30 gallons of water went somewhere. We cleaned up what was on the floor but it was no where near 30 gallons. We have a crawl space, but haven’t gone under the house yet to see if it leaked through there. We have a fan on the area where there was standing water (about a four foot area up against an interior wall) but what else can we do? I read through your Q&A and understand that we should get a dehumidifier as well. Any other thoughts or suggestions?

A: At this point all you can do is try and dry it out as quickly as possible an wait to see how it affects the floor. I don’t know of any magic wand for something like this.

Flooded prefinished Brazilian cherry flooring

Q: We have 7 year old 3/4 inch prefinished Brazilian Cherry flooring on our entire first floor. Recently, we had a toilet break and overflow, flooding a large area of our floors. We had a company come dry it out with fans and dehumidifiers for 5 days, but there is still visible cupping. Is there any chance the cupping will go away and the floors will flatten out with time? Insurance wants to repair by refinishing, other sources tell us that is a bad idea due to prefinished coating and the micro-bevel that will require the entire first floor of the house be sanded. The original floor distributor is out of business, so matching it will be difficult. I’m clinging to hope that the floors will flatten with time. Any advice is appreciated!

A: I have occasionally seen a floor flatten. But you’ve had a significant section of the floor affected with a significant amount of water. You are going to have to wait a while for this to properly dry out. Don’t forget, because it is pre finished, much of that water went between the boards and soaked the sub floor. That sub floor is going to take quite a while to dry out because the water will have to evaporate it’s way through the jatoba. My recommendation would be to pull the floor out and replace it after the sub floor has been exposed and allowed to dry. At this point, you can’t even consider sanding these floors, and they would have to be monitored over time with a moisture meter to see what the moisture levels in the wood are. It can take weeks to dry out with that floor in place. And the existing floor has now swelled and after it dries it is going to shrink big time. If the installers used staples you might also face the issue of broken tongues. You pay insurance for years and never use it. Now you need to. Replace the floor.

Fixing water stain on bamboo floor

Q: I have an engineered vertical carbonized bamboo click floor (made with plywood, not paper). A few weeks ago a small amount of water oozed out of my dishwasher and sat on the flooring. The bamboo sucked the water in a few inches at the crack between the planks, and though it seems to have dried out it left small a darkened, grayish area near the ends of the planks. Is there any way to get rid of that darkening? How do you fix a water stain on bamboo floor? Thanks very much!

A: That seems unusual because products from China are finished on all four sides. Given the slight amount of water this is strange in any case. You will probably have to sand the spot clean to bare bamboo and refinish the entire board.

How do we repair/flatten the hump without removing the entire floor?

Q: We have a brand new home with hardwood flooring throughout. The builder installed the furnace in the attic. The condensation hose was faulty and water poured onto the hardwood flooring below. This resulted in a huge buckle/hump along one row of the hardwoods, smack in the middle of a room. How do we repair/flatten the hump without removing the entire floor?

A: At this point, if it is confined to 2 rows of boards, cross your fingers and hope it all equalizes and flattens out. If there was a lot of water involved, which it sound it was, it may also be wise to just pull up the damaged area and let the sub floor dry out. Then have it repaired and the floors re-finished.

Follow-up Q: My ultimate question is: How do I pull up or ‘flatten’ the two rows, in the middle of the room, without pulling up the entire floor? (I just want the ‘pyramid in the middle of the room’ flattened.)

A: Easy to remove a row or two. Make 2 power saw cuts down the centre of one of the rows and pull out the boards. Also, there is still a possibility it will eventually flatten on it’s own.

(Dirt) crawl space causing waves and humps in hardwood floor

Q: Our hardwood floors are wavy, and in some places have humps in them. We have lived in this house only 5 yrs. It was a new home and had no problems until last summer. I called and got advice and installed a dehumidifier in the crawl space. This thing runs all the time. Last summer water was dripping off ducts, no doubt it was moisture. So here is the problem: my floors want return to normal. Rh in home is 53 and under home 55. This is Alabama, so it gets really humid. Any advice? Would a dehumidifier upstairs help? Should I run the AC more often? (we keep it at 75 to 77 most of the time.)

Is it time to sand down? Although the big humps may be from the subfloor, who knows.

A: If it’s a dirt crawl space I would definitely lay a heavy tarp over it and ventilate the crawl space so you can get air exchange in there. A dehumidifier on the main floor couldn’t hurt.

Similar Q: My grandparents home was built in the early 50’s, in southern Louisiana. It’s a wooden home built off the ground. The crawl space is only about 2 feet and the problem is the flooring. It is hardwood covered with plywood and commercial tile.

The tile is cracking, and the plywood is wavy. It looks like water damage, but it’s throughout the house. There was a leak under the house about a year ago. All the plumbing is under the house. There are no signs of additional leaks. The crawl space has been closed off on the North side of the house to help with winter heating. Parts of the ground are moist, some are not. What could be the cause of this flooring problem?

A: I’m not sure why someone would cover hardwood with plywood and tile, both of which are of less value than the hardwood floor?

You need to control the moisture from beneath the house. Heavy tarps over the dirt is a good place to start. Make sure the area is ventilated. I don’t know if the hardwood can be saved, but I would remove all floor coverings down to that and take it from there.

Heavy rain caused a huge buckle in our floor

Q: Heavy rain caused a huge buckle in our wood floor. The past two times it has done this, the floor flattened back out. This time, wood appears to be drying in the buckle form. What can I do?

A: It may look dry, but there may still be a lot of water beneath it. If this was near a wall, you could try removing the last board nearest the wall. If it doesn’t flatten, obviously you will have to have the area lifted and repaired. Fans, dehumidifiers and heaters may all help to dry it out more quickly.

Expanding dark spot(s) on wood floor

Q: I have engineered wood floors that have been here since I moved in 8 years ago. There has always been one dark spot that kind of looks like a burn mark (as if someone placed something too hot on it). Now this spot has grown larger and there are two new spots (about 3 to 4 inches across). All the spots are are equal distance from each other, in a line about 3 feet from each other. They are not moist and they are not soft. What causes dark spots on wood floors?

A: It sounds like water marking, but this would require a constantly present water source, and I would expect to see other signs of damage such as cupping if this were the case. Could it be mold? Again, it is my understanding that for mold to grow or spread it also needs the environment of wet and warm. I’ve posted a question about this on a forum but thus far nobody else has chimed in on the issue.

Follow-up Q: I thought about mold as well, but of course as noted the spots are not damp or spongy. One of my thoughts is that since they are in a a straight line pattern but about the same distance from one another that it may be water/mold from the where the water line runs under the concrete slab and may be possible these spots are where some joining or connection is made in the water line. Maybe there is a slow/low leak and very little or no water gets to the top surface, only the resultant mold. On the other hand, I am not sure of the path of the water line. I may call the water company to confirm this water line path to exclude this theory or take it to the next step. (Glad I purchased that water line insurance two years ago).

I also thought about pet stains, as the previous owner had a small dog that was left alone for long periods of time. If there were pet urine stains that were treated and the floor refinished, could they dark spots reappear a few years later if the pet stains were not correctly treated/cleaned?

A: I’ve sanded plenty of floors with pet stains and other water marks. They either can be sanded out or they can’t. BUT, they don’t grow and they don’t reappear after they have been sanded away. I think your first theory is likely more on track. If it is correct, I guess it will mean removing at least part of the floor and chopping up the concrete. The scenario you mention with the water line makes good sense to me. Have someone put a meter on those spots and reference them with other areas of the floor that don’t have spots. If there is water you will get a higher reading on those spots.

Webmaster’s note: we recently had a job where old pet stains were being kept damp by vent condensation from below, and it stunk to the high hills. We’d never seen old, WET pet stains before. It made me think of this Q&A.

Related Q: I had bamboo flooring installed five months ago and I just noticed dark spot coming from under the baseboards, it would appear to be moisture stains. How do I get rid of the dark marks?

A: The more important question you should be asking is “where is the water coming from”? You may have to sand or scrape off the black mark.

Black, moldy floor boards (under mat for dog’s water dish)

Q: I have hardwood floors… I just changed a mat that I keep under my dog’s water dish. It is a waterproof mat, so I thought that moisture wouldn’t go through it. Anyway, lifted mat up and there are some black, moldy looking areas. I wiped, cleaned, used vinegar and water, but to no avail. Stains are still there. Is there anything I can do to clean moldy wood floors? (I have prefinished hardwood that was laid on concrete slab.)

A: I think you will probably have to either refinish the affected boards or replace them. Not an easy thing to do, given that it is pre-finished. You might try oxalic acid to remove the stains but, if it works may also lighten the board considerably compared to the surrounding ones.

Replace or sand a severely water damaged floor?

Q: Our water dispenser recently spilled on our prefinished Birch hardwood floor and caused damages to a large area of the floor. We have 2 suggestions from the original hardwood company and a contractor from insurance company re: wood floor water damage. The original hardwood company suggested to replace the damaged area and the insurance contractor suggested to resand the whole floor and stain with Bona water product.

Can you please give us an advice of what is good or bad about each choice? What options should we go with for the good long term? Our floor is about 2.5 years old and still looks relatively new.

A: It really depends how serious the damage is. I have seen floors like this flatten out given time. I don’t think the floor area needs to be replaced unless there is severe gaping.

Follow-up Q: The hardwood floor is damaged seriously (i.e., it cups a lot) in a large area. We are going ahead with the fix. My question is that should I sand and restain the whole floor or it is better to replace.

Replace: the prefinished stain is more durable? Is it correct?

Sand and stain: because of the serious damage, does the sand work for a long term? Or will it cause gaping and squeaking later on? Also, how long does the stain stay?

A: As I mentioned, cupping is one thing, but large gaps is another. If there are large gaps between the planks I would replace the floor. A cupped floor can be sanded flat. However, it needs to be verified that the floor is dried out and back to a normal moisture content range before any sanding is attempted. Otherwise the wood will crown, which means it reverse cups. I am not a great fan of pre finished floors. Aluminum oxide and ceramic coatings are more abrasion resistant than any finish currently available to me. However, this can become very problematic down the road when the floor eventually will need to be re-coated. There are finishes on the market, available to professionals that offer excellent durability, so I wouldn’t be concerned about that. To be honest, I am not that big on ******** finishes either. Aside from Traffic which is a 2 part water borne using an iso-cyanate cross linker, their other finishes are for low end use. I have been using Poloplaz Primero oil modified which is the best finish I have ever used. It is very tough. In the water borne line they have a product called 202 which is intended for industrial/commercial applications and is almost half the price of Traffic and safer to use since it doesn’t contain iso-cyanate.

The only way a stain would become damaged is if there was no finish on the floor, exposing the stained wood for a period of time.

Second Follow-up Q: Thanks a lot for your answer. We lean toward replacing the large area with the same material because there is too much disruption if we go with resanding according to the contractor (we’d have to be out of the house for 3-4 days).

Do you see any downside with replacing the large area with the original material?

A: I don’t see any problem provided the colour matches. You will be using a different lot batch to do the repairs and depending how long your floor has been down and amount of direct sunlight it may have changed colour to some degree.

Nail holes are showing black stains

Q: I recently bought a house and pulled the carpet off the floors. There were beautiful hardwood floors underneath. I pulled the carpet tack strips off carefully from the edges and filled nail holes with wood putty. I applied an oil-based polyurethane and the floors turned out nice. However, as time has gone on (3 months) several of the nail holes are showing black stains around them that were not present at the time of finish. Do you know how these are caused? Also, is there anything I can do at this point to get rid of them?

A: The carpet had probably been shampooed in the past and moisture collected around the nail and left the black water mark. You can recess the black area with a nail set and fill with colour match putty. I like the tube filler/caulking from Color Rite.

Floor camel-backing

Q: I have a lot of lift on my floor. I think it’s called camel-backing / camel backing; like, the floor is a little hilly in some spots as if the staples have come out and now the floor is lifting. What is the cause? How do I fix it?

A: Is this something that has just developed? Is it possible you have a water leak and it is expanding the boards and causing it to heave?

Removing water stains on wood floors; sanded and still have water stains!

Q: I have a question about removing water stains on wood floors. I have sanded a floor. Now I have to remove some water stains that are still visible. How do I do this without more sanding?

A: Some water stains won’t sand out regardless of how deep you go. In such cases you have a choice of either staining the floor dark, replacing the damaged area or using a very strong bleach such as oxalic acid.