Date: 2007-09-28
By Gene Wengert, wooddoc@uwalumni.com
Q: We have some furniture with a tongue-and-groove panel design. The individual pieces are much like oak flooring. The problem is that we have trouble holding them down because they are buckling. We are very careful about storing our incoming lumber in a low humidity room, as we are in Florida. Our wood comes kiln dried from the Appalachian area. What are we doing wrong?
A: The rule is that wood does not change its size or shape unless
its moisture content changes. So, the swelling and resultant
buckling you see is due to an increase in moisture content. I
am delighted to hear that you are making a special effort to
store the kiln-dried lumber in a dry location. What's happening
is that the humidity that the furniture is exposed to in
coastal Florida is higher than the humidity in your lumber
storage room. The result is moisture gain and swelling.
However, we could probably accommodate some swelling without
any problems if you didn't assemble the individual pieces so
tightly.
In other words, do not put the tongue all the way into the
groove. Also, only fasten the pieces at one edge -- blind nail
the groove edge. If you fasten the piece tightly, it will not
be free to expand with changes in humidity. I think that your
dry storage is okay, although perhaps a slight increase in
humidity (5 percent RH) might be a reasonable change.
Incidentally, if you store the wood in a more humid location
and then ship the furniture to Minnesota in the winter, the
furniture pieces might dry out and shrink, which could expose
part of the tongue which is unfinished. Therefore, do not raise
your storage humidity too much. Also, make sure that you finish
the individual pieces before assembling them together so
unfinished wood will not be exposed if the pieces shrink.
Gene Wengert, "The Wood Doctor," has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.
Updated: Oct 21, 2011
This article appeared in FDM, February 1999. ©Copyright 2012, All Rights Reserved.