Stains on Hardwood floors

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Forum topic by ChadR posted 03-27-2012 11:17 AM 14939 views 0 times favorited 7 replies Add to Favorites Watch
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80 posts in 2439 days

03-27-2012 11:17 AM

Topic tags/keywords: wood finish sealer stains hardwood

I have been working on my new house. The floors were painted black, very poorly. After sanding for several hours I think I found the reason why the previous owners painted it black. There are a lot of very dark stains in the hardwood floors. I went over the floor with a random orbit sander and a dremel floor sander. I stared with 28 grit, then 36, 60, 80, and 100. The stains would not come out.

I was wondering if anyone had any suggestions for removing these stains. I wanted to put on just a hardwood finish and keep the light color of the wood with out any polish or stains. Is that going to be something I can do or because of these stains am I going to have to use a dark wood polish?

Here are some photos.

-- Some people have a way with words... some people... not... have way.

7 replies so far

View patron's profile


13600 posts in 3303 days

#1 posted 03-27-2012 11:30 AM

try bleach on an area that will be covered
with some furniture later

i’m sure there are products out there
but bleach is the cheapest

oak is bad with stains
even water from indoor plants make it stain black

just give the room plenty of ventilation

good luck with this

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View crank49's profile


4030 posts in 2933 days

#2 posted 03-27-2012 12:42 PM

My dad was a hardwood floor finisher for over 50 years. He would have cut those floors down with his big 5 hp American/Clark sander using 0000 grit (four ought) paper. The strip around the walls that couldn’t be reached by thr 8” drum on the American/Clark he would sand with a spinner (now called and edger); a hand held tool that looks like a giant router with a 8” diameter sanding disk on the bottom. All that sanding takes about 1/8 inch off the surface of the floor. Then he would crawl around over the whole floor and reset all the nails by hand. Finally he would seal this rough surface with a mixture of sanding dust and shellac. After this dries you sand and finish like a regular un-painted floor.

Even with all this there may be some stains that go too deep to sand out. If thats the case you may have to change your plans and put a stain on the floor to blend out and mask the discoloration you don’t like.

View marcosvillamontes's profile


32 posts in 2144 days

#3 posted 06-06-2012 09:19 PM

if the stain goes really deap into your flooring then sanding will be of no help. The only remedy is then to bleach out these stains. You can also stain your flooring in a similar color, or replace the damaged parts with another piece of wood… Anyway, here you find comprehensive information on how to stain, refinish, clean and repair a wooden deck . Here is also a video that shows you step by step what to do and how to proceed, which tools to use, how to stain. Good luck with your staining job!

here is also a good instructive video for you:

-- Marcos Villamontes, Santa Cruz,

View 404 - Not Found's profile

404 - Not Found

2544 posts in 2931 days

#4 posted 06-06-2012 10:20 PM

Someone put me onto Oxalic acid before.

Just copied and pasted the instructions which might be of interest to you.

Dissolve 12 to 16 ounces of oxalic acid crystals into one gallon (or 2-4 oz. in a quart) of hot water.
Use solution while hot, with a scrub brush.
Apply liberally allowing solution to remain on surface until desired lightness has been achieved.
If solution cools before job is finished, reheat solution (do not boil).
Triple rinse thouroughly with clean water
and allow to dry.

To remove stains:

When completely dry, lightly sand the surface. Surface must be clean and completely dry (not just surface dry) before refinishing.
Incomplete drying and retained subsurface moisture can cause finish adhesion failure.

After Stripping and to Lighten:
To restore wood tones (especially for oak)
Restore clarity and the natural tones of the wood without effecting the patina. Use 3 to 5 oz. per gallon of hot water then apply by spray, brush or wipe on. Rinse thoroughly with clean water.

Danger: Contains oxalic acid.
Avoid contact with skin and eyes.
May cause burns or irritation.
Harmful if swallowed.
DO NOT allow solution to get into gloves
or soak through clothing to skin.

Give 1 or 2 glasses of water
and call a physician immediately.

Flood with plenty of water for at least 15 minutes; get medical attention promptly.

Wash thoroughly with soap and water.
If redness of skin occurs, discontinue use and consult a physician promptly.

Keep out of reach of Children.

Never store in unlabeled containers.
Close container after each use.

Oxalic Acid
Wood Bleach

Bleach Bare or Uncoated wood.

Remove black water spots
and tannin stains.

Gently lighten wood tones
darkened by age or finish.

Poison! May be fatal if swallowed.
Causes eye and skin irritation.
May cause burns. Do Not breathe dust.

Keep out of reach of Children.

Mix oxalic acid Wood Bleach with hot water to effectively bleach unfinished or stripped wood quickly and easily. The bleach lightens wood
and is excellent for removing black water spots and tannin stains in wood.


Read all information on container.

Mix With Water Only!

Protect eyes with goggles.
Wear rubber gloves.
Protect Skin from splashes.

Wood must be clean; free of paint, waxes, oils,
and dirt. Use wood cleaners to remove any grease oils or grime. Use paint strippers to remove any finish, paint, or coating.

ALWAYS test results in an inconspicous area—dilution may need adjusting for desired results.

Difficult stains may need repeated application.

Wood Finish Supply
Email: • • • Internet:

Return to: New Product List

View DrDirt's profile


4423 posts in 3704 days

#5 posted 06-06-2012 10:54 PM

As above – go the oxalic acid route first – it is specifically reduces (the black tannic acid) back to wood colors.

Bleach will work, but it is also: (1) damages the wood fibers, and (2) not real deep penetrating

Best would be to douse it with the oxalic acid solution – I got mine from Ace Hardware and it came in a paper cylinder about 1/2 the size of a can of comet/dutch cleanser powder.

Mix it pour it on. I found on cherry, that had gotten bits of iron, from being near the grinder, it got rid of the black spots in about 1-2 minutes.. almost the reverse of watching photographs develop in the tray.
Then bleach the bad spots.

-- “The two most important days in your life are the day you are born and the day you find out why.” Mark Twain

View dhazelton's profile


2746 posts in 2258 days

#6 posted 06-06-2012 11:50 PM

Someone effed up that floor, for sure. You can bleach it but it will never look like a new floor. Just try to keep things in perspective, accept character, remember that rugs and furniture will likely fill the room and don’t obsess.

View KarenW's profile


131 posts in 2150 days

#7 posted 06-07-2012 03:17 AM

I’d go with oxalic acid, too. I’ve used it on badly blackened oak and maple with terrific results.
Just make sure you wear a respirator when sanding – the dust can be extremely irritating.

-- Happiness does not come from doing easy work but from the afterglow of satisfaction that comes after the achievement of a difficult task that demanded our best. --Theodore I. Rubin

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