Bleaching Wood

[Gary Wyngarden]

I'm to the point in the wood restoration project on my dinghy where I need to bleach the wood to remove water stains. These resulted from poorly bedded fasteners installed by the boat's builder (it's less than two years old).Yesterday I bought some oxalic acid crystals to do the bleaching and Borax to neutralize the acid after the bleaching is done.My question is this: The directions on the oxalic acid crystals say to leave the acid on the wood for 15 minutes. I've been using Rebecca Whitman's Brightwork The Art of Finishing Wood as my guide on this project. She says to leave the acid on for 24 hours before neutralizing it and rinsing it off.So which is it--15 minutes or 24 hours (a nice narrow range)? Anybody with experience doing this want to render an opinion?Thanks for your help.Gary WyngardenS/V Wanderlust h37.5

 

[RichH]

Leave it on until you get the color you want

If you cover the oxalic solution with a synthetic felted material or open cell foam, add more oxalic solution to the 'felt' then cover the whole shebang with saran wrap.... this will keep the oxalic acid solution from drying and will effect a better and more consistant bleaching. Test the felt or sponge with oxalic so to be sure that it will not extract color from the felt/foam and transfer it to the wood. The felt will hold the excess amount of oxalic, the saran will stop the evaporation of the water. Oxalic usually bleaches instantly unless the stain is very deep into the wood. If very deep and you tried oxalic with not good results, then sanding/scraping is the usual next action. How to mix oxalic: take hot water and mix in the crystals until no more crystals will dissolve, stir and add more crystals until they wont dissolve. Caution with oxalic: it rapidly absorbs through bare skin, concentrates and rebuilds its crystals .... in the nephrons of your kidneys. WEAR GLOVES

 

[Warren Milberg]

Gary

I've had good results using oxalic acid on teak, but perhaps like Rich suggests below, I've found the key to best results is keeping the acid moist on the wood. I've never left it on for more than 15 min and found that time ok. The only problem I ever had was letting the oxalic acid dry on the wood in the sun. That resulted in a "spotting" on the teak and necessitated a lot of sanding to get the surface uniform in color. Good luck.

 

[Rich]

ditto on the gloves

I've used the premixed version of oxalic acid that gets sold as "teak cleaner" in the chandleries and can vouch for the need for gloves. Also, the spotting will be a problem if you let it dry out.15 minutes would seem like a bare minimum--it takes at least that long for the solution to penetrate to the bottom of a deep stain--but I don't see the need to go more than a couple of hours unless the stain is one of those deep rust stains from a chain or something. Using one of those "pot scrubber" sponges is a good way to be able to scrub without damaging the surface.