Bleaching Blue Stain

      Advice on using bleach to clean lumber affected by blue stain. August 31, 2009

I have some blue stain on small portions of stock I'm milling for some interior doors and rather than cull the stock I am trying to use sodium hypochlorite to bleach the color of the blue stain. It works reasonably well, at least enough to allow me to mask the residual stain during finishing. My question is once I apply the bleach do I need to spray on a baking soda solution to neutralize it, and then wash with clean water? I tried this and the soda turned the area brownish compared to spraying on the bleach and washing it off with fresh water.

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Water washing is suggested as wood does turn color when exposed to strong alkali.

From the original questioner:
Gene, so the sodium bicarbonate step is not necessary then, only water wash?

From Gene Wengert, forum technical advisor:
I do not know if it is "necessary" or not. I just know that it will change the color of wood - some woods more than others.

From contributor D:
Try the two part bleaches that employ peroxide as their oxidizer. I feel that they yellow the wood less than the chlorine type bleaches, which are made strongly alkali in order to stabilize the mixture.

From contributor G:
In a BC study, hypochlorite proved best for blue stain bleaching.

From Gene Wengert, forum technical advisor:
I also have heard that hypochlorite does better.

From the original questioner:
There are three good alternatives for neutralizing hypochlorite bleach: bisulfite or metabisulfite, thiosulfite, or peroxide. I'm not sure where to get metabisulfite so I will try it with peroxide. Hopefully it will not discolor the wood like the baking soda solution.

From contributor G:
You can get potassium and sodium metabisulfite at the wine and beer-making supply place and thiosulfite at the photography supply store.

From contributor G:
The chlorine component of the hypo will gas off by itself, leaving the NaOH (caustic) component to be neutralized, or washed off with copious amounts of water. At the pulp mill, we used SO2 injection to get rid of chlorine, but you don't want to do that at home.

From contributor T:
I get the best results with Klean Strips two-part bleach #WB-19. Use it just prior to finishing as it does not penetrate deeply, and you might sand off the bleached wood if you apply it prior to sanding. Do not use it on eastern red cedar. Try it on a test piece of any species you have not yet used it on. It works great on pine.

I use it on flame box elder from logs that get blue stain in summer, and it works fantastic. I was afraid it would diminish the red pigmentation but just the opposite was the case. It brings out the red, whitens the sap, and almost totally eliminates the "denim". However, many of my customers ask for the denim stained wood specifically.

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