Though you cannot altogether prevent wood from interacting with moisture in the air, you can learn how to deal with wood shrinkage or expansion, which is the invariable result. In its natural state, wood is wet and will shrink considerably after drying. Lumber that you purchase at the store will already have undergone a drying process either through air drying or kiln drying in ovens. But even dry wood will ultimately interact with the moisture around it, causing wood shrinkage or expansion that may cause drawers to stick, doors to jam, or surfaces to crack, hump or cup. Luckily, there are tips for how to deal with wood shrinkage and expansion to counter the problem before it happens.
- Always build with the grain facing the same direction. One way to deal with wood shrinkage or expansion is to ensure that the wood warps in the same direction throughout the wooden piece. To that end, always construct wooden frames with the wood grain facing in the same way. As the wood absorbs or loses moisture, it will shrink or expand in the same direction, keeping the integrity of the wooden frame intact.
- Always build with the end grains facing the opposite direction. As wood shrinks or expands, it may twist or develop several types of humps that will mar the finish of a tabletop or the side of a cabinet. To prevent such deformities from developing, lay two pieces of lumber one on top of the other during construction, the first with the end grain facing up, the next with it facing down. The result will be to create counter pressure on the lumber that will keep the surface leveled despite wood shrinkage or expansion.
- Always leave room for mobility. When fitting the top or sides of wood furniture, allow room for the mobility associated with wood shrinkage or expansion. Fix the pieces firmly at one end, driving screws or nails into the wood structure below. Then, at the opposite end, fit the screws or nails in the slots between the lumber sections, to allow the wood beneath to move without cracking or cupping the wood above.
- Always select lumber by its annual rings. When buying lumber, pay attention to the angle of the annual rings. Flat rings, which are more frequent, are indicative of tangentially sawn lumber which is more likely to warp than radially sewn lumber, in which the rings will be at 90 degrees to the face of the board. Alternatively, construct wood furniture with the annual rings alternating between facing up and down, as this will create counter pressure on the wood grain, preventing it from warping through wood shrinkage or expansion.
- Use Frame-and-Panel construction. The most popular construction method for dealing with wood shrinkage or expansion is to create grooves for the lumber to sit in and freely expand. For example, a tabletop would be constructed inside a grooved frame that is deeper than the width of the panel, leaving the wood room to shrink or expand without cracking or warping.