Q. What makes cabinet doors stick? We have several theories thrown around in meetings, but we want the truth.

A. The key to answering this question is, “Wood in use does not shrink or swell unless its moisture content changes.” When the moisture increases, wood swells and when the moisture decreases, the wood shrinks. So, a sticky door is one that has swollen -- swollen since the cabinet was made.

To assist in your analysis, solid wood only shrinks or swells in width and thickness; lengthwise movement is rare, very rare. Composite wood products, like MDF, plywood, particleboard, etc., move in all directions. In fact, if many of these products are wetted with liquid water, they tend to swell in thickness quite a bit, as the water is relieving some of the stress when the product was compressed when it was made.

So, you now have enough information to analyze your particular situation. You need to answer the question “With a cabinet door that is rubbing or sticking, is it the door that's gained moisture and swollen, or is it the frame or other wood components holding the door that are shrinking and pulling the door closer to an adjacent door of component?”

For example, if MDF is used for the main components of a cabinet, and this MDF has been stored in a humid location (which is not suggested) before manufacturing the cabinet, the MDF can swell a bit before use and then when put into use, it will shrink to the low moisture condition that is typical of a house or office. With this shrinkage, the door opening becomes smaller. So the cause of rubbing is drying of the cabinet itself, not the door.

On the other hand, with solid wood, the entire door frame is made with pieces that run lengthwise, a direction in which solid wood is stable, so the door opening is essentially fixed in size. Rubbing is therefore because the door has swollen.

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.