We’re going to look at wood movement in an effort to close the “expectation gap” that many people encounter when planning a project involving wood. Although we can’t change the reality that wood moves, we can learn to anticipate it and make the most of it. When we do, not only will we be better able to appreciate the inherent beauty of real wood, but we’ll also be able to steer clear of some of the typical problems related to incorporating wood in your project. We will start with a general overview of wood movement.
Basics of Wood Movement
You can understand the basic concept by picturing a bundle of straws; a tree’s fibers are made to absorb moisture from the ground and carry it throughout the tree. Once a tree is felled to the ground and cut into logs, those same straw-like strands remain. The freshly cut ends of the lumber will start to shed water as it is milled. To return to our straw analogy, when each straw-like strand loses moisture, it will contract and become narrower. Until the wood achieves equilibrium with the moisture content of its surroundings, the fibers will continue to expand as they absorb moisture and similarly contract as they release the water.
Reducing Wood Movement
A board’s fibers will continue to expand and contract as the humidity levels change, even after a particular board achieves equilibrium with the environment. Numerous techniques can be used to slow down this process, but it cannot be stopped; in fact, any attempts to do so may lead to case hardening, which in turn can lead to structural issues like cracking. Although careful kiln drying can lessen extreme fluctuations in moisture content, careful drying of lumber at a slow pace is essential.
Movement of Wood Varies Depending on Species
Tangential shrinkage and radial shrinkage are the two primary types of shrinkage that take place. The most significant amount of shrinkage is known as tangential shrinkage, which is measured by how much the wood travels along the growth rings and results in side to side swelling of the straws.
Radial shrinkage is the migration of wood along medullary rays, which originally carried nutrients to the interior of the tree, or perpendicular to growth rings. A general ratio of tangential to radial shrinkage exists for each type of wood, and the closer the ratios are to being equal, the more stable the species will be. It is more likely for species with T/R ratios that are drastically different from one another to experience warping and cupping.
You might be wondering what can be done if wood movement cannot be stopped. You can prepare for it and take action to reduce it. You will be reducing that “expectation gap” we previously addressed as you plan out your project involving wood when taking into consideration and implementing adequate preparations regarding wood movement. Knowing what you’re up against will help you make wise plans. In Part 2, we’ll go over the reasonable actions you can take to safely minimize the amount of movement.
J. Gibson McIlvain Company
Since 1798, when Hugh McIlvain established a lumber business near Philadelphia, the McIlvain family has been immersed in the premium import and domestic lumber industry. With its headquarters located just outside of Baltimore, the J. Gibson McIlvain Company (www.mcilvain.com) is one of the largest U.S. importers of exotic woods.
As an active supporter of sustainable lumber practices, the J. Gibson McIlvain Company has provided fine lumber for notable projects throughout the world, including the White House, Capitol building, Supreme Court, and the Smithsonian museums.
Contact a sales representative at J. Gibson McIlvain today by calling toll free (800) 638-9100.