How to remove Dark black water stains from wood

[Sterling Wong]

Hello

Last year I made tables out of birch plywood for a restaurant patio however some of the tables have deep black water stains.

I have sanded off the coating and tried oxide paste (bar keepers friend) and it doesn't seem to work well.

I would like to know what other effective options there are and if staining would help cover it up

The tables are in its natural color and have not been stained.


Thanks

[Bill Orbine]

Bar Keepers Friend contains oxalic acid. However, I don't know what strength the the Keeper has over straight up oxalic acid you can buy in hardware stores. You ought to try that.

However, it also depends on what you have for a stain. Oxalic acid works good with iron stain. But the stain could be mold.... In which you could use chlorine or peroxide.

Birch plywood ( or simply birch) is not agood choice for patio furniture. It does not hold up well and is prone to rot and insect as well as get moldy. Sure, you can protect with finish..... but no finish is bullet proof.

[Carl Kona]

Sterling,

Here is a video on removing the stain with oxalic acid. But he warns against using it on veneer as it could delaminate.

https://www.youtube.com/watch?v=NNFQDOz5kmo

[David Utterback]

I just tried to remove similar stains from maple. In addition to barkeepers friend, I tried chlorine bleach and Zinsner's wood bleach. None of them worked although each did noticeably lighten the wood color.

[John C Bush]

If you can find "Superoxol"-- brand name for high concentration hydrogen peroxide~~35%--it may be worth a try. It is good at removing black/dark stains of organic origin. No sure if the black stains are iron oxides tho. Be a bit careful--it will blanch tissue.

[Sterling Wong]

I just added images to my first post of the black stains on the table.
I'm not sure if it is actually mold now.

[Wayne Lomman]

Looks like sooty mold to me. Scrubbing with a stiff brush and an acid cleanser is the best option which may work. Acid actually removes the offending material. Bleaches just render it invisible so it is much more likely to return. Have you tried chemically stripping the finish rather than sanding it off? You may get the result in one go. Use a decent industrial stripper, not a retail one. Also, replace the finish with a different product. Cheers