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Seasoning FAQ
HAVE YOU READ OR HEARD?
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“Air-dried lumber can’t have a moisture content below 15%”.
Not true unless you live in the Amazon Jungle! Your lumber and the projects you construct from it will dry to the indoor
EMC (equilibrium moisture content) of your locale. In our area that is
8-9% MC, for warm coastal areas like Florida it is 11-12%.
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“The reason why kiln-dried lumber is so widely available is because of demand for its superior quality”.
The predominant availability of kiln-dried lumber is because it’s more economic for the distribution channel (hardwood sawmills, wholesale distributors, etc.). The driving issue is not Quality but the concept of Time equals Money. You can kiln-dry 4/4 (1”) Red Oak stock to
8% MC (moisture content) in about 4 weeks, 12 weeks for 8/4 (2”) stock. Under the very best conditions air-drying takes about 18 weeks (northern locales average 6
months) for 4/4 stock, 3-4 years for 8/4 stock. Thus, you can begin to sell your lumber (get your inventory money back) four
or more times faster by kiln-drying instead of air-drying. Now add the demand of the major furniture manufacturers who use special glues requiring extremely low MC to glue-up itsy bitsy pieces which are then used as boards for their ‘solid Walnut’ furniture.
Our opinion is that kiln drying serves
the lumber industry (reduced inventory $$, greater inventory turns) not
the woodworker. After all old world craftsmen used air dried lumber to
build furniture which has survived 100 or more years. |
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“Lumber that has air-dried for 3 years has really only dried for 1 year and then sat for the other 2.”
Proper air-drying involves a two-step process - outside drying to about
20% MC; then the lumber MUST be moved indoors for the final drying to EMC (equilibrium moisture content), which in our locale is 8-9%.
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"Air-dried lumber is less
dimensionally stable then kiln-dried lumber"
Other than how a lumber board is sawn - plain, quarter, rift (a
whole other subject matter), the greatest factor in dimensional instability is
amount of difference between the MC of the board at the time it was milled and
the EMC of the locale where it was milled. All lumber and assemblies made
from it (furniture for instance) will season to the EMC of its location.
The greater the difference in board MC and locale EMC the greater the change in
cell structure as the seasoning takes place. The greater the change in
cell structure after milling the greater the change in the board's
dimensions i.e. dimensional instability.
Thus, to use our locale (which has an EMC of 8 -9%) as an
example. A lumber board sold as 6% MC kiln-dried (but it's really not at
6% if it sat around in an un-climate controlled warehouse after coming out of the kiln) is actually
more dimensionally unstable than our air-dried lumber.
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"Air-dried lumber is more
prone to Case Hardening"
Case Hardening refers to the stress in a board when there is
an uneven moisture content between the outside and inside
cellular structure. The
outside cells are substantially drier than the inside cells and in effect
provide a moisture barrier which slows or precludes the drying of the inside
cells. The outside "Case" is in effect
"Hardened". The board looks fine until it is milled.
Once the inside cells are free of the barrier and begin to dry the board can
make dramatic movement as the inside cells lose their excessive
moisture.
The primary cause of Case Hardening is drying
which has occurred at too fast a pace. When done properly, air-dried
lumber is LESS prone to Case Hardening because the whole drying process is
slower.
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"Your air-dried lumber is not
steamed"
Isn't that great! We do not "steam" our lumber. Steaming is
another industry practice done for the benefit of the industry - not the
woodworker. Steaming allows the industry to sell Sapwood at Heartwood
prices (i.e. sapwood is graded as heartwood). As purists who desire
the "old world" natural lumber we believe steaming grays and dulls the color
palette of the lumber, reduces its patina, and reduces the beautiful grain
contrast which makes Walnut Lumber the "King of Cabinet Woods"
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