Removing Stains from Wood Floors

      Suggested ways to remove stains from floors without deep sanding. November 28, 2014

I am refinishing this red oak wood floor. This is a private adventure but I am a professional cabinetmaker. It was badly stained but I was hoping for the best. I have literally taken an eighth of an inch of material off this floor and the stains remain. Iím using a Clark drum sander with 20 grit so that is not the problem. This floor was covered with carpet for 25 years. The tenant of 15 years just moved out. Everywhere her kitty peed, a staple was removed, or where plants were there is a black stain. I am guessing this is a chemical reaction with tannins in this wood. Can anyone recommend a good way to polish this - bleach, stain, chemically darken? Sorry about the low quality pics.

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Forum Responses
(WOODnetWORK Forum)
From Contributor O:
The black stains are indeed a dye that results from the combination of iron (ferrites), acid, moisture and the tannins in the wood. It will go as far as the staples and a bit further. The presence of cat urine will lead to only one solution - removal.

From the original questioner:
This is the finished product. I took easily 3/16 off this whole floor. Iím amazed stains can run that deep - live and learn. Edging is going to be fun since I went so deep. Hopefully a dark stain and satin finish will make it passable.

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From contributor F:
Oxalic acid solution would have removed 95% of those stains! It will likely remove the existing residue so a dark shouldn't be necessary. Good luck. Next time ask first, you have to know you didn't encounter a unique situation.

From the original questioner:
Thanks - I'll try it. Having done a couple of hours of web research this is the first I have heard of oxalic acid. It must be a trade secret.

From the original questioner:
Not sure if anyone is going to read this but I wish I had found out about that acid before spending hours sanding unnecessarily. I still have two rooms to go so that will help.

From contributor K:
Wood stains having two categories: White rings and black marks. Both are caused by water. The white rings arenít so stiff to take care of. Apply a pad of very fine harden wool and saturate it in a lemon oil. The lemon oil wonít eliminate the stain, but it lubricates the steel wool so that it doesnít graze the wood. Now very softly polish until it shines the white ring with the finest steel wool.

From contributor Y:
The white stains can easily be removed by a fine steel wool and some lubricant to protect the wood. You can probably use lemon oil for this. As for the black rings, the best remedy would be to sand it off and bleach it then refinish it again. Sand the surface to remove any finish that protects that wood. Then you can start to apply bleach to the wood using a paint brush. You can leave it overnight for better penetration. You can sand it again to make the wood smooth and refinish it with your choice of top coat.

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