Blue Stain in Red Oak

A discussion of staining, drying odor, and related problems in a large oak tree blown down by wind. December 12, 2008

I have recently been asked to saw up some sizable red oak logs. The customer can't get to them right now and wants to wait somewhere between 1 and 3 months to saw them up. The logs are about 36" at the butt, and 42' overall length. I haven't had any experience with red oak at all where I am, and consequently don't know whether or not it will blue stain like others will. She also said that others had told her that while air drying, in a barn or other semi-enclosed area, it smells like vinegar. She is worried that it will smell so badly that she won't be able to live in the adjoining living quarters of the barn. Can anyone help me out with this so that I can relay the message to her?

Thanks to WOODWEB for all of the insights I have gotten in the past. I have learned an awful lot about this profession. I intend to build at least two solar kilns and probably a third and much smaller solar kiln in the upcoming months.

Forum Responses
(Sawing and Drying Forum)
From contributor W:
Regarding the blue stain, are you talking about blue stain that you see in the logs right now or blue stain that appears after sawing? Blue stain in the logs right now means metal you get to cut while sawing the logs. Blue stain that develops on the lumber is a result of the tannic-acid-rich log moisture mixing with the iron of the saw blade. Cooling water enhances this, contributing more moisture to the chemical reaction. The resulting blue/black from this reaction is as deep into the wood relative to how much time the iron and tannic acid were present. The blue resulting from sawing should plane away in one pass. The blue from the nails or fencing in the logs will not plane away. Itís there - that vinegar smell.

Although it may not really matter, what species of red oak are you dealing with? That lovely smell is just part of it. If the logs are from trees that had a certain fungal infection, the lovely smell becomes more like vomit. Again, just part of it. The smell does go away or subsides as it dries and will likely not be smelled in its end use form.

From the original questioner:
Thanks for your reply. I was speaking about the type of stain that is in a log that sits too long on (or off) of the ground. Something akin to what pine does over time.

With reference to the smell, you mentioned that it would go away over time as the wood dries. What amount of time would she have to put up with that smell - a month or two, or will it hang around for much longer than that? The wood will be dried in east Texas if that helps any.

From contributor W:
That blue stain is mold. Not to be a smart-axe or anything, but there is really only one thing to avoid the mold - make lumber. But now that I truly consider the Texas part of the equation, in one to three months from now, I would think the logs would degrade so much (from drying) that the yield of lumber from the logs would tank. I would advise you to get them sawed as soon as you can or find a way to submerge them to keep them 100% saturated. The really tricky thing to consider in all this is what happens to the log as it sits there over time. The half of the log closest to the ground will experience a lower range of temperature change during 24 hours because the ground acts like thermal ballast which will aid in retaining more moisture, promoting mold. The top half is getting baked and losing lots of moisture quickly. This is going to result in warped, twisted, un-pretty boards, and heartache. Hate to see you and your client lose good wood.

From the original questioner:
I last spoke with her last night, and she said that the butt of the log at least was still attached to the uprooted stump still in the ground. Apparently a tornado went through there and ravaged a few of them. Do you think that still being attached to the roots will help with the degrade that you mentioned? I think she wants to mill them some time next month, but she wasn't sure that her schedule would allow it. Also, did you have an idea about the amount of time with regards to the smell?

From contributor W:
I would think it should quit smelling foul in two to four weeks. Because I donít think of that smell as foul or unfavorable, I donít notice it like your client will and havenít really applied a period of time to how long the smell lasts. Nonetheless, Iíd be shocked if longer than a month, as long as they are sticker stacked well.

I do think the degrade will still happen, but maybe not as bad since the log is off the ground. The bottom half of the log is still sheltered by the top half. The top half is still taking most of the abuse from the sun and drying faster. Warp and twist will still likely occur, but maybe not so bad.

This just came to mind! If the tree was wind thrown with the root plate still intact, the tree is still technically alive and it could, in a sense, be kept on Ďlife supportí until you got to it. Water, water, water.

From the original questioner:
Many thanks for helping me! I was thinking that very thing, although sight unseen, I don't know how many roots are still attached.

From contributor L:
Who says it has to be dried in the barn? Stack and sticker it outside, cover it to keep off the rain and sun, maybe using shade dry cloth or burlap on the windward side to slow the drying slightly so there will be a little less degrade.

From contributor S:
I agree with contributor L. If the smell is an issue, just put it on sticks outside. Put some old metal roofing on top. A landowner I know had a lot of wind downed oak trees. They leafed out real well the first summer, not so much the second, and he had a guy pull the logs out after that. Any maple trees he had were somewhat stained, but the oak was in good shape. Note that the trees were in the woods and in the shade. Even if the sapwood gets stained in red oak, with 36" logs, you can throw that away and still have plenty of good lumber left. I once had a customer ask me for blue-stained pine for a kitchen he wanted in a vacation home. Never did see how it came out...

From Professor Gene Wengert, forum technical advisor:
Blue stain is not mold (which only grows on the outside of lumber). It is a fungal infection, however, and it is eating the sugars in the sap. As a result, it is found only in the sapwood. In fact, it is sometimes called sap stain. It can develop in the log and will affect the resulting lumber within a week under warm conditions if the lumber is not drying.

Note that in Texas, it is common to find sapwood in red oak that is 4" wide, so even in a large log like you have, you are talking about a lot of poorly colored lumber. And this outer sapwood lumber will be the clearest too (potentially the most expensive). (If you have 4" wide sapwood on a 36" log, it is like having only a 28" log if you get a lot of stain. I would not want to throw that much wood away.)

From your description, it is possible that some white rot might also develop. Iron tannate stain (or just iron stain) is a reaction of iron and tannic acid. It does not go deep in most cases. It can be quickly removed with oxalic acid (also called wood bleach).

What has not been mentioned is that you may also get gray stain, which is a complex enzymatic oxidation reaction (mainly in the sapwood) where the sugars and starches are oxidized, similar to the browning of an apple that has been cut and exposed to the air. If you have warm weather, it is likely that this gray will permeate the sapwood. Note that it is not fungal.

A log that is still attached to the roots will not degrade much as the bark will prevent any drying. I have never heard of the type of warping (drying defects) that contributor W described from a stored log. Logs are stored at sawmills for months sometimes without such things happening. Any of the logs that are separated from the roots should be end coated to prevent end drying.

The aroma in the barn would easily last for a month or more. In fact, sometimes it may last for many months if there is some bacterially infected wood in the lot.

In this respect, a barn is not the best place for drying oak as there is not enough air flow, so the RH will be too high during the daytime. Air drying under an open shed would be best. If not, then go with what contributors L and S stated.

From the original questioner:
"What has not been mentioned is that you may also get gray stain, which is a complex enzymatic oxidation reaction (mainly in the sapwood) where the sugars and starches are oxidized, similar to the browning of an apple that has been cut and exposed to the air. If you have warm weather, it is likely that this gray will permeate the sapwood. Note that it is not fungal."

This is what I think we get a lot of in the pecan we cut here. I have been doing an awful lot of reading about solar kilns and drying in general, and it appears to me that the slower you dry wood until it reaches about 20% MC, the less chance of defects. Which just so happens to go along with what I have learned the hard way about drying some of our woods. I had originally advised against drying outdoors for this very reason. I don't, however, have any experience with oak. I cannot dry pecan outdoors because it just seems to dry too quickly and leave a lot of checking and warping. We place our wood in a shipping container, and leave the doors almost closed until the MC reaches at least 30%, and then open them a little farther until 20%, and then full open (to the south wind) after that. I will have to check on it, but my understanding is that the "barn" is not fully enclosed, but rather has some sort of breezeway in it.

Am I way off base with my thinking or am I reasonably close in assuming that it needs to dry slower until it reaches about 20% MC? Thanks for your help.

From Professor Gene Wengert, forum technical advisor:
4/4 northern red oak would be safely dried at about 2.5% MC average loss per day. Southern oak might be slowed a bit. For more info, check "Drying Oak Lumber."

From contributor D:
Two years back I was given a storm tree, red oak, that was 5' diameter and over 240 years old. I ran into a blue streak that was found to have a flag mount buried 6" inside. Also old lead bullets from past hundred years. The stump stood 24+ tall. As cutting into boards, the smell only lasted till the surface was air dry in a few weeks. Leaving it outside to dry then moving it into the barn next year would work. I also lumbered out a 4ft diameter white oak that was down for 3 years and it was still wet inside and made great quarter sawn boards. All I cut is qtr sawn lumber.

From contributor G:
Contrary to the post stating the blue mold shows up only on sapwood, the blue mold I'm experiencing shows up only on the heartwood! Happens to be water oak.