As we discussed in Part 1, lumber movement cannot be completely stopped. As part of the same natural design that provided nutrients to the tree while it was living, the medullary rays once used to deliver nutrients throughout the tree serve a purpose in milled lumber, as well, continually allowing it to come into equilibrium with the moisture levels of its surroundings.
While this process actually provides for stability, it can also produce warping. While you can’t stop moisture, you can take measures to decrease or slow the wide swings that lead to disfigurement of lumber.
Wood Movement Reduction
First, you’ll want to avoid leaving lumber in direct sunlight; instead, always stack lumber in shaded, well-ventilated areas. Ideally, you should also insert small pieces of lumber between boards to allow air flow throughout the pack (which is called “stickering”). If you take the time to sticker the wood, you’ll be allowing each board to evenly absorb and shed moisture, giving it the best opportunity to acclimate to its environment.
After you have the lumber stacked at your job site, you’ll want to give it at least a few days to arrive at an equilibrium with environmental moisture levels before installation.
If you’re using kiln-dried lumber, the lumber you’re receiving will already have ideal levels of stability.
But depending on the difference between the climate of the lumber yard from which the boards have been purchased and the local climate at your job site, the wood may still need a little time.
If you’re planning to cut the wood before installation, you’ll want to give those fresh cuts some time after cutting the lumber and before building it into a fixed position.
Wood Movement Comparison
As much as you may think you do, you really don’t want to stop all movement, or you’ll also be compromising the wood’s stability. Instead, we can be thankful for the predictable movement of wood, which is quite unlike the kind of movement demonstrated by composite decking, as a result of the plastics and wood flour cores from it is made. Without grain, the wood flour expands in unpredictable ways throughout the “boards.”
With composite decking, the plastic outer shell is stretched, as a result of the expansion, but when the wood flour sheds moisture and shrinks, the plastic shell does not. That separation between the shell and wood flour core leads to uneven warping along each board. The uneven swelling also means that each joint and cut end swells more than the remainder of the deck or boardwalk.
Kiln drying, proper ventilation and air drying, end-sealing, and treating can all reduce wood movement, but at the end of the day, nothing can stop it. But at least we can predict wood movement and even count on it — something we can’t say with such confidence about manufactured materials.
Read the Entire Series
- Imperfect, Perfect Lumber: Lumber Continues To Move, Part 1
- Imperfect, Perfect Lumber: Lumber Continues To Move, Part 2
- Imperfect, Perfect Lumber: Large Timbers Will Have Cracks, Part 1
- Imperfect, Perfect Lumber: Large Timbers Will Have Cracks, Part 2
- Imperfect, Perfect Lumber: Lumber Continually Gives, Part 1
- Imperfect, Perfect Lumber: Lumber Continually Gives, Part 2
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 representative at J. Gibson McIlvain today by calling (800) 638-9100.
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