On 6/6/2013 1:58 PM, Greg Guarino wrote:

I was under the impression that the most important factor is the
change in moisture content rather than the absolute amount. That's why
I wondered why "sealing" the wood doesn't work. Apparently the answer
is that "sealing" does not in fact prevent all moisture migration in
and out.

Correct .. a finish will only slow down the process, but will NOT
prevent the process.

The key factor in a wood reaching and EMC (equilibrium moisture content)
is RH (relative humidity) of its environment.

Some things to note:

1. Wood does not shrink or swell in use unless its MC changes. Read this
again, as it is so important. Wood's MC changes when the RH around the
wood changes. Of course, if the wood is at the wrong MC when first put
into use, it will adjust to achieve equilibrium with its environment and
therefore may shrink or swell initially quite a bit.

2. Another key point is that the MC of lumber, as well as shop
conditions, should be such that the wood, from lumber to finished goods,
will change less than 2 percent MC after drying, in storage, in
manufacturing and when put into service.


Here's a handy download:

http://www.fpl.fs.fed.us/documnts/fp...chapter_13.pdf

And another treatise on moisture content of wood in use:

http://www.fpl.fs.fed.us/documnts/fplrn/fplrn226.pdf

That entire Forest Products Laboratory is a gold mine of wood related
information for both construction and furniture uses.

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KarlCaillouet@ (the obvious)