How do I remove black stains from oak?

[Chad Stucke]

I have a rental house with oak hardwood floors.

We were sanding it and cant get the black stains out from the entry to the kitchen area.

It seem's like we usually sand some more and it eventually comes out but not this time.
I think that the oak has reacted to whatever water or oils or iron that soaked thru the carpet over the years. Any suggestions?

Today before we left we applied a 50% bleach water solution hoping to lighten it up thinking that at this point we couldn't hurt it.
I have read that a strong oxalic acid solution(30%) will do it but I am not sure where to get it. Or if it works.

If you know what to do let me know.
Thanks in advance,
Chad

[Richard M. Wolfe]

I can't say that I have any extensive experience with decoloring agents but oxalic acid should be what you should use in your case to remove stains from oak as a result of a reaction of tannins in the oak. There are three types of bleaching agents for wood. Household chlorine bleach generally has very little effect on the wood and are used for surficial organic material. Oxalic acid has been outlined. Wood bleach is two parts - hydrogen peroxide/sodium hydroxide (lye), which will remove color from the wood, which is not what you want.

[Jeff Mackay]

I'd say the only way to get rid of 100% of the stain is to replace the stained boards. I've tried very diligently to remove some water stains from maple with bleach. I thought it looked great until I put the finish on it. The floor looked like stained maple that was bleached :( Now granted, maple isn't oak, but I think th same principle applies.

It really isn't too difficult to replace boards if the staining isn't too widespread.

Jeff

[Chad Stucke]

The floor would be hard to match it is made up of 9" tiles that are 4 pc of hardwood and are turned 90 deg. every tile.
I am looking to save what is there.
Chad

[Dell Littlefield]

I had really good luck in using oxalic acid on some stained teak. It might do the trick for you on the oak. Most paint stores and the larger Ace hardware stores keep it in stock. It's worth a try.

[Prashun Patel]

Are you sure you've sanded enough?

[Steve Jenkins]

Definately try oxalic acid. It is sold in many stores as wood bleach. one brand name is Savogran and it is in a white and kind of orange red container. It is in crystal form and you dissolve it in hot water. If there is no finish over the stain usually when you wipe on the oxalic acid you wipe off the stain. Pretty amazing to see.

[Kent Parker]

Chad,

We used to use oxalic acid to remove dark staining from spruce and fir when refinishing spars. Around here you can purchase it in crystal form and mix your own saturated solution in warm water. Its pretty fast acting and you generally do not allow the wood to dry. Let it stand 10 to 15 minutes then wash out. A little scrubbing may be needed.

Very important that you wash out the acid with fresh water after the stains disappear otherwise any finish coats applied over will show the area that was bleached. It would appear "milky" if you didn't get all the acid out.

Cheers,

Kent

[Howard Acheson]

Oxalic acid is the bleach to use to remove mineral and water stains from wood. You can buy it in most paint stores and I have seen it in a big box on occasion.

Follow the directions on the label.

It may not get all the stain up, but should get most of it.