Long-Term Storage of Air-Dried Lumber

      Air-dried lumber left in drying stacks for long periods without kiln-drying is at high risk for insect damage and spoilage. June 18, 2010

I often hear of people using their air drying piles for wood storage, for decades or more. My thoughts have always been to get the air dried wood inside once EMC has reached 12% or so. I sticker stack my air dried in my air treated shop until MC drops below 10% and put up in the lumber lofts. What are your thoughts on this?

Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Air drying for more than 30-45 days for most species will increase the quality loss (color, checks, stain, warp) and risk of insect damage. It is best to do it as you are... Move it to a kiln or final drying situation.

From the original questioner:
Quality loss (color, checks, stain, warp) and risk of insect damage is due to... increased chances of the lumber getting rewetted while outdoors?

From Professor Gene Wengert, forum technical advisor:
Wetting from rain, melting snow, etc. and sunlight drying (too dry) are the major factors causing the damage. Insects do like wetter wood, so the longer the wood is above 10% MC, the better the chance of insect damage.

From the original questioner:
Thank you, Dr. Gene.

From contributor F:
Due to the economy, I think we will be building inventory for a few years. Could the wrapping used to ship lumber be used to protect it from the elements for say 2-3 years? I realize this is very general considering the vast number of species, sizes, thicknesses, etc. I thought of air dried to 12-13% and storing it rough.

From Professor Gene Wengert, forum technical advisor:
Air dried lumber stored for 180 days or more even when protected from sun and rain will have such a high risk of insect damage that it is not a good idea. Some species, like ash, will be nearly 100% ruined. Once an infestation gets going, it is hard to control. Once an infestation is noted, there is usually a lot of damage inside the wood that is not evident. Insecticides do not work; borax might work and might be legal, but the cost (applied to wet lumber) would not be easily absorbed.

From contributor F:
The questioner mentioned storing the air dried in a loft. Does storing indoors lessen the danger of insects? In the past I have lost stacks of logs and lumber to insects. I am in central Ontario. One year, saw flies went through a stack of pine logs like a family of midget beavers. Our cold climate gives us some reprieve. Can putting the lumber back into the kiln depending on the cycle of the insects cause a lot of damage to the lumber?

From the original questioner:
My lumber storage loft is inside my air treated shop. RH is less than or equal to 50%, so the MC of my lumber should be at or below 9%, I believe. Comparing dried lumber to logs is not the same - would take decades or longer for large logs stored to dry to 10%.

As I understand insects and heat, you could reheat your lumber to 135*F lumber core temp for several hours and kill all bugs and their eggs. Will need to keep reheated lumber below 10% MC to keep the critters at bay from your lumber.

Have heard of wood guys purchasing buggy wood, re-drying and selling to a specialty market, like antique dealers (?).

From contributor F:
Will putting the lumber back in the kiln with sufficient time and temperature cause case hardening?

From Professor Gene Wengert, forum technical advisor:
Nope. Impossible.

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