Lumber

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.

One of the challenges of working with large timbers is their tendency to crack. At the very beginning of this discussion, a disclaimer is in order. There’s really nothing you can do to completely prevent large timbers from cracking. There are, however, some proven strategies that can lessen the number of cracks that develop in these timbers. First, we’ll take a look at reasons why your large timbers are prone to developing cracks. Then we’ll go over some strategies to try to keep them from excessive cracking.

Reasons Why Large Timbers Crack

Cracks in timbers, also known as “checks,” are a naturally occurring phenomenon that won’t actually hurt your wood. It’s easier to regulate checking in smaller sized lumber. Large 12/4+ sized timbers that include a significant cross section of the log they came from can tend to pose a bit of a challenge when it comes to preventing cracks.

The reason why these cracks develop is that large timbers take much longer to dry out than smaller timbers. This leads to uneven drying from the outside to the inside of the board. As the outer layers dry quickly while the inner layers retain moisture, checking will happen as a matter of course. Denser woods check more often than less dense species. The depth of checks will also vary from species to species. Ipe, which is commonly used in decking projects, tends to incur plenty of checks, but those checks are normally relatively small.

Steps to Help Prevent Large Timbers from Cracking

1. Seal the Ends of Timbers

Sealing the ends of large timbers can help to keep them from cracking. This should be done as soon as possible after the timbers are cut. Because water moves rapidly along wood grain, sealing this area off will be one of the most effective ways to stop significant checking from occurring on large timbers.

2. Allow Time for Proper Acclimation

This point really cannot be stressed enough. In order for wood to perform well, it must be properly acclimated to the environment of its final destination. For effective acclimation, store it in a shady area, up off the ground, using spacers for up to a week or two. Covering it with a tarp is also a good idea.

3. Apply a UV-Inhibiting Sealer

Another way to help prevent checking on large timbers is to apply a UV-Inhibiting sealer to the boards. This sealer can be applied before or right after you install your decking. It can help to keep the sun’s harsh UV rays from causing surface checking on your wood.

Some people who want to try to prevent a large timber from cracking will saw a slit, known as a “kerf,” into the wood. This method goes all the way back to the practice of ancient Japanese temple builders from as far back as 600 BC. The kerf will help to release pressure from the wood, which can prevent cracks from forming elsewhere. But in order for kerfing to work, it must be done before the wood even starts the drying process. Since most dealers don’t have the opportunity to work with timbers that are that fresh, kerfing simply isn’t a viable option at most United States lumber yards.

Final Observations

Though you can take all the necessary precautions to try to prevent cracks, a certain amount of checking is bound to take place, especially on your larger timbers. Because it’s an organic material, wood will always move over time. Often checking occurs long after installation. When it does happen, don’t panic. This is perfectly normal, and won’t hurt the structural integrity of your wood. These cracks can actually release tension and leave your wood stronger than ever before. It’s the wood’s way of shedding itself of excess moisture. Look at it as part of the charm and beauty of working with a natural product.

J. Gibson McIlvain Company

As an active supporter of sustainable lumber practices, the J. Gibson McIlvain Company (www.mcilvain.com) has provided fine lumber for notable projects throughout the world, including the White House, celebrity homes, luxury yachts, Capitol building, Supreme Court, and the Smithsonian museums. For more information on J. Gibson McIlvain’s lumber products and services, call Monday thru Friday toll free (800) 638-9100 to speak with one of their lumber representatives.

If you regularly purchase different species of wood you may notice some surprising cost discrepancies when comparing Walnut to other species. Exotic imported species such as Mahogany can often cost less than Walnut. Many customers seem puzzled that a domestic species would be more expensive than a prized imported species, especially one that is as challenging to find sources for as Mahogany.

Why is Walnut Relatively Expensive?

The difference isn’t between the availability on the market, but on the nature of the different trees. Mahogany trees tend to grow very large while Walnut trees do not. Mahogany also has a much longer growing season than Walnut does. So when you look at these types of differences, it’s a bit easier to understand how the domestic Walnut wood could sometimes be higher in price than the imported Mahogany in spite of import costs.

Walnut vs. Maple

In order to get an easier to follow comparison, let’s look at the Walnut species compared to Maple, since Maple is another domestic species that readers of this article should be familiar with using. It grows in the same region as Walnut, but the two trees are extremely different from one another in several significant ways. For example, Maple is hearty, grows large quickly, and is a competitive tree. When Maple grows nearby other slower-growing trees, it has a tendency to become dominant.

If a Walnut tree grows too close to a Maple tree, the Walnut tree can end up small and possibly experience starvation as the Maple takes over the area. Walnut trees do best when they have plenty of room to receive sunlight. If trees from a more hearty species surround a Walnut tree, it normally won’t reach its full growth potential. Under these conditions, a Walnut tree will typically only reach 30 to 70 feet in height.

Then there’s the factor of heartiness. Maples are notoriously hearty. Maple trees are able to withstand plenty of wind compared to Walnut trees which are not very wind-resistant. This is another factor to consider when it comes to the cost of Walnut wood when compared to other domestic and imported species.

Walnut’s Natural Challenges Translate to Lower FAS standards

The above-mentioned problems which Walnut trees face cause them to grow branches that are closer to the base of their trunks than other domestic species such as Maple or Oak. As a result, the FAS (Firsts and Seconds) grading system has been adjusted for Walnut. Wood without straight grain and that includes plenty of knots will qualify as FAS grade Walnut even though such conditions would not be considered FAS quality for similar domestic species. It’s important for lumber dealers to explain this to customers who may not be familiar with the unique aspects of Walnut lumber. They’ll need to understand that the grading system for this particular species is vastly different than for other species from the same growing region.

In spite of these peculiarities, Walnut is still considered a prized species by furniture makers. In this application, the knots, swirls, and variations of Walnut are considered to be a strength of the species rather than a weakness.

J. Gibson McIlvain Company

As an active supporter of sustainable lumber practices, the J. Gibson McIlvain Company (www.mcilvain.com) has provided fine lumber for notable projects throughout the world, including the Supreme Court, the White House, celebrity homes, fine musical instruments, the Capitol building, and the Smithsonian museums. For more information on J. Gibson McIlvain’s lumber products and services, call Monday thru Friday toll free (800) 638-9100 to speak with one of their lumber representatives.