installing crown molding
Photo: David Carmack
Q: My wife and I renovated our family room one summer, and the following winter the joints in the crown molding opened up, even though they were nailed and caulked. The gaps look awful. Is there anything we can do to fix them?
Nate Collins, Bridgewater, N.J.

A: Norm Abram replies: Caulk and nails won't hold joints together if the wood wants to shrink. The problem could be that the molding's moisture content was too high when it was installed and it shrank when the heat came on, or that your house is too dry, or both.

In your area, the molding should have a moisture content between 8 and 12 percent when it's installed, and the relative humidity in the house should be 35 to 40 percent during the winter. If your inside air is drier than that, crank up a humidifier and see if the moldings tighten up when the air reaches the correct level. Don't expect a change overnight; it takes a while for the wood to swell.

If your humidity is already in the proper range, caulk any gaps inch or smaller. For gaps larger than that, consider replacing the molding and starting over.

Here are a few things to keep in mind if you do replace it: Install the new molding in the spring or the fall, when the humidity is moderate. Prime the pieces on all sides, including any cut ends. And use cope joints in the corners and bevel joints on the runs. (See how to cut copes.) These steps will go a long way toward keeping wood movement in check.
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