Q. Can dry humidity in a home cause oak furniture to face check or crack? These are within the wood pieces and not at the glue joint.

A: No. A piece of furniture made from well dried wood cannot have low humidities in the home initiate new checking in the wood.

Here are the reasons:

1. The strength of dry wood is nearly twice the strength of green wood. Plus, the tensile strength of dry oak is over 15,000 psi. Initiating a check requires large stresses.      

2. The maximum moisture changes between manufacturing at 8 percent MC and then a home at 5 or 6 percent MC is very small so there would be a very small amount of shrinkage or shrinkage stress. Such stress can occasionally cause warp, but will not cause or initiate new checks.

3. It is all too common to see some checking when air drying oak lumber. These checks close and become virtually invisible after kiln drying and prior to finishing. They do not heal however. Exposure to low humidities, such as in a home during the heating season, can reopen these checks and can make them longer, wider and deeper.

The low humidities in some finishing ovens can dry the surface and cause some shrinkage and opening off these checks, but often the checks will close soon afterwards. Oftentimes, the checks can be broken open and the inside of the check will reveal that stain and/or finish is inside the check, meaning that the check was created and existed prior to finishing.

Note that exposure of dry wood to liquid water (such as in a flood) and then subsequent drying can create new checks and/or open old checks.

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.

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