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Green wood/wet wood

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Forum topic by Clarence posted 04-21-2010 06:25 PM 1545 views 0 times favorited 3 replies Add to Favorites Watch
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Clarence

125 posts in 1850 days


04-21-2010 06:25 PM

Jayman raised the question earlier about how to make dry wood wet. I have a related question; it may be a dumb question but I’m a dumb guy and don’t know the answer.

It is stressed over and over here that your wood should be at a proper dryness (don’t remember the percent) before you build it into a project. I’ve read that it takes a long time—-a couple of years or so—-to achieve that by sticking and storing.

Is drying from “green” different from drying from “wet”, such as if your storage shed develops a leak and your stash gets soaked. Is getting dry wood wet again just like starting over from square one, or will it dry out much quicker?

-- Getting old is a good thing, but being old kinda stinks.


3 replies so far

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Michael Murphy

448 posts in 1749 days


#1 posted 04-21-2010 06:47 PM

Here's a good article about it.

If you rewet some dried lumber it’s not the same type of moisture content as the original cellular moisture in green wood.

-- Michael Murphy, Woodland, CA.

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millmgr

27 posts in 1856 days


#2 posted 04-27-2010 09:24 PM

When freshly felled logs are sawn into lumber, water can account for more then half the weight of the wood. So green lumber can start out with over 100% moisture content! Air drying will allow the free water (between the cells) to migrate to the surface and the ends and evaporate, leaving mostly cellular water and moisture content in the 20% range. Kiln drying uses heat , air flow and humidity in a controlled manner to remove the cellular water without damaging the wood structure or causing stress. The industry standard for hardwoods is 6-8%. If the wood gets wet from a leak in the roof, you will get some surface moisture that should evaporate over time. You may get some checking of the surface as it dries.

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Nomad62

726 posts in 1702 days


#3 posted 04-27-2010 10:51 PM

Green wood is a living tissue dying, it takes time to do so as well as losing the water content. From green to dry the wood will warp, twist, etc. more so than drying from having gotten wet from contact with water (after having been dried). The “green” will go away even if the wood sits out in the rain, but of course the wood will not dry out. Most people will want to air dry their wood at least until the green factor is gone, say to about 25% Mc or so, then kiln dry down to around 6%. Once there it will re-absorb moisture to the point of whatever the local atmosphere is, usually averaging 12 to 15%. If water from rain or a shower head or whatever hits it, then it will obviously become wetter but will dry out much more quickly than the original dry time. Kind of like a sponge. The absorbtion and evaporation will certainly check the wood as it will expand and contract accordingly, but only at the surface level as it only penetrates so far; hence the use of finishes. A finish, by the way, will only slow down moisture movement in either direction, it cannot be stopped.

-- Power tools put us ahead of the monkeys

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