Stain in Maple -- Prevention and Cure

An explanation of why maple wood stains, ways to slow the process down, and how to bleach stains out. July 28, 2006

How long can maple be stored in log form with temps in the mid to high 60 degree range, without worry of the wood staining or getting that blue hue?

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Three days, maybe five.

From the original questioner:
Is there any way to stop the staining for any length of time, say a month or two?

From contributor D:
Gene, what if he debarked the maple log and Anchor-Sealed the whole log? A lot of work, yes, but would that not slow down the staining? Two to three months of spring - early summer weather is pushing it, I'd think.

From Professor Gene Wengert, forum technical advisor:
There are two stains of interest. One is fungal and that will penetrate anywhere there is an opening (ends, branch stubs, missing bark areas). If you could seal the log, you could stop this fungal stain. If you could keep the log under water, it would help. The other is a chemical stain where the starches and sugars oxidize, forming a grayish stain. This does not need oxygen and begins as soon as the log is cut. It goes faster when the temperature is higher - twice as fast for every 20 F. End coating will not help. The only thing, besides rapid cutting, is keeping the logs cool.

From contributor J:
Once the graying or fungal staining has occurred, is there any way to reduce the visual damage? I have 700 board feet of curly maple with this problem.

From Professor Gene Wengert, forum technical advisor:
The chemical stain can be bleached with wood bleach (oxalic acid).

From contributor P:
Gene, could you go into a little more detail of how to use the acid on curly soft maple that has gone gray? How deep into the wood does it work and how much to apply, etc.?

From Professor Gene Wengert, forum technical advisor:
Wood bleach will affect only the surface (perhaps 1/100" deep). Follow the instructions on the can, etc. After use, the surface must be washed or neutralized... follow the instructions. The finishing forum moderator here may have more information for you. We used to bleach frequently "in the old days," but I do not see it much today.

From contributor J:
Thanks for your time and information. This gives me hope.

From contributor C:
Gene, can you explain the causes of the fungal and chemical stains a bit further? Specifically, how can the starches and sugars oxidize without oxygen? By oxygen, do you mean exposure to outside air? Could it be from the moisture that is naturally present within the log as water is made up of hydrogen and oxygen? This would negate the use of end sealer. Thanks for your help.

From Professor Gene Wengert, forum technical advisor:
Oxidation is a chemical term. It involves several chemical steps. The reaction being at very high MCs. The final step or steps occur at low MCs when there is plenty of air. If the initial reaction does not occur at high MCs, then the oxidation cannot occur later. Incidentally, the reaction requires an enzyme which is a catalyst. So, the reaction is sometimes called an enzymatic oxidation reaction. Fungal stains are really caused because the fungus itself is dark colored. Check the archives here for more info.

Causes and Cures for Stains in Dried Lumber

From contributor A:
I tried to find a source for oxalic acid a few years ago and was unable to. It works great to remove glue clamp stains on panels. Do you know of a source?

From Professor Gene Wengert, forum technical advisor:
Try your local pharmacy or your local high school chemistry teacher. All bottles that are in the mill must be properly labeled and have documentation and so on, so never have them make more than you need for the moment.

From contributor H:
Another source for oxalic acid is a marine store. It is great for removing stains on fiberglass gel coat (especially rust). I know that West Marine always has it. Think that I will try it myself. Thanks, Gene.