Wet Cottonwood with Wind Shake

      Some comments about the dubious strength and quality of lumber from Cottonwood logs having noticeable wind shake. July 28, 2006

Question
I have been milling Eastern cottonwood for a few weekends. Some of them show no shake, and some are like the picture. Will there be more separation as the wood dries, or is this the end of the problems? It's basically a throwaway when they're this bad, but I am able to get a couple of 2*12's out of a log like this. The lumber as-milled shows no problems. Curious as to other experiences. Many of the older buildings on this farm were made from cottonwood 2*X lumber years ago, and it's in good shape.


Click here for full size image

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
The shake results from anaerobic bacteria that reduce the wood's strength. They also cause wetwood at the same time, so the MC in these areas is often over 100% MC. In addition to shake, there will be a strong, foul odor and discoloration. Drying high quality is nearly impossible. It is common to find that the shake worsens a bit in drying, but not a whole lot.

The shake arises when the roots are damaged and the tree is in a wet area. The bacteria move about 1-1/2" per year up the stem, so we see it only in older trees. You will find more info if you do a search in the archives.

Cottonwood can be used for structural purposes, but it is not exceptionally strong. Hence, studs are okay, but joists and so on are questionable.



From the original questioner:
Thanks, Gene. Yes to all of your first paragraph. It smells like a horse stall during milling and handling. These trees are from a river bottom area that floods 4-5 times a year. The one in particular had a family of raccoons living in the upper branches, and it was actually starting to lose its bark. Moisture, you say? When falling these trees, the water will literally run out of the stem, and during milling, the water sprays out 2-3 inches in front of the blade.

I did an archive search a while back, but don't remember seeing anything about windshake showing up after drying, so I got my question answered. Thanks.

The American Wood Council website lists cottonwood in the span and load calculator. I had planned on using those numbers.



From Professor Gene Wengert, forum technical advisor:
Bacterially infected wood, and this includes the wood in and around the shake area, is very weak, so the span tables would not apply except for wood that is not infected. It is always a good idea to find out if the local building inspector will ask for the wood to be graded... I do not know of anyone qualified to grade cottonwood, so you will really have to look around. Note that the span tables are for various grades, so even if you do not have the lumber graded, you do need to know the grade so you can get the correct span.


From the original questioner:
Thanks, Dr. Gene.

"Bacterially infected wood, and this includes the wood in and around the shake area, is very weak, so the span tables would not apply except for wood that is not infected."

Does this mean a tree that is not infected, or to stay away from the infected area? As stated, a 2*10 cut from the jacket, or flitches from this lumber appears to be structurally sound, but they're green. If I get too close to this decay while sawing, the board will fall to pieces.

I have no formal inspectors to deal with. Could I lean the backhoe on a couple of these after they're dry, and mechanically grade them, as well as visually?



From the original questioner:
When used for rafters, stay away from obviously badly infected logs or regions within a log. I do not know about the testing procedure you indicate, but the span tables are based on deflection issues, so if you have weaker wood, it will bend too much. The strength is likely several times more than you will need.

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