do take time before we see any issues,
a week or two at the least, and maybe
longer. We also know that moisture
losses cause shrinkage and shrinkage
results in cracks or splits. So, we want
to make sure that our wood is quite
close to the driest expected condition
of 30 percent RH, or 6.0 percent MC.
On the other hand, small amounts
of swelling often do not create severe
issues. Plus, when we switch from drying to moisture gain, there is about a
1 percent MC delay before the wood
begins to swell.
So, targeting a little bit on the
dry side is OK, as with the delay, even
though the humidity is 50 percent RH,
the wood actually behaves as though it
was only 43 percent RH. The bottom
line is that small moisture changes in
use with the average 6. 8 percent to
7.0 percent MC target will not create
defects in most products.
Note that if you are shipping to a
humid climate like Florida or a dry climate like Colorado, you might indeed
want to adjust your target.
If that is not reasonable, then consider storing the products in your shop
in a small room with walls sealed with
plastic sheets and with a high RH for
Florida or a low RH for Colorado.
Then any defects that develop can
be fixed before shipping rather than in
the field. Further, after your week-long
test in the controlled humidity room, if
you wrap the products in plastic wrap
or bags, you know that the MC will not
change one bit, because moisture cannot get in or out of the wrapping.
Finally, your kiln operation needs
some attention, as it is virtually impos-
sible in standard kiln to achieve an
average of 5 percent MC. Such lumber
would be extremely brittle when ma-
chining and would not glue well.
So, you are being told incorrectly or
the operator is measuring MC incor-
rectly. To measure these low MCs, the
operator would have to use an oven
test, or use a pinless meter. The pin
meter is not very accurate under 6. 5
percent MC. ;
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