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.
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