There are some ugly black stains caused by water on some of the woodwork on my boat. How can I remove them?
Don Casey responds:
Your best shot at getting rid of the black is oxalic acid. You can buy it in crystal form at most hardware stores or marine equipment suppliers. Dissolve some of the crystals in warm water and paint this solution onto the wood. Let it sit for a few minutes, then wash it off. It may take more than one application.
If the stains resist oxalic acid, the big gun is hydrochloric acid, the active ingredient in most two-part teak cleaners. This stuff will bleach the wood, but it also dissolves it, so using it on veneer is a risky proposition. If your alternative is replacement, then you don't have too much to lose and a lot to gain by experimenting with one of these products. Follow the instructions, and keep this stuff off painted surfaces. Using it inside the boat is problematic, but it can be done if you plan your strategy carefully.
The bad news is that sometimes the veneer is oxidized all the way through, and bleaching just doesn't work. Hopefully your stains aren't that deep, but if they are, gluing on a new layer of veneer is probably the best option to have a better looking surface.