Wood movement causes heartbreak when projects crack and warp. Learn how to master these simple techniques and save yourself some nightmares.
When humidity is high, wood absorbs moisture and swells. When humidity drops, wood shrinks. This “movement” is gradual, so you probably won’t notice weekly changes. But seasonal changes cause problems you can’t miss, like sticking doors, ugly gaps in woodwork or a crack in a tabletop.
This movement occurs whether wood is fresh from the mill or centuries old, whether it was kiln dried or air dried. And it exerts tremendous force that’s almost unstoppable. But with a little knowledge, you can minimize the consequences.
This article will explain the basics of wood movement and show you real-world solutions.
LET IT MOVE!
If your plans don’t accommodate wood movement, you’ll end up with trouble, like this cracked tabletop.
So here are the 4 main issues you have to deal with.
1. WIDTH MOVEMENT IS THE MAIN ISSUE
Wood moves as its moisture content changes. Wood doesn’t move much lengthwise, so you don’t have to worry a lot about boards getting shorter. But a board can move quite a bit across its width. A board that’s 6 in. wide during a humid summer might shrink by 1/32 in. in winter.
That’s not much, but it’s enough to cause a crack in a tabletop or gaps between floorboards.
2. MOVEMENT IS CAUSED BY MOISTURE CONTENT
When wet wood dries, it shrinks. The amount of movement is determined by the type of wood and the degree of change in its moisture content. Applying a sealer or paint can moderate wood movement. But it’s nearly impossible to seal wood so completely that its moisture content stays constant.
3. WOOD CAN ALSO CHANGE SHAPE
Movement within a board isn’t uniform; one section might move more than another. That leads to warping, twisting and cupping. Most of these changes happen in the initial drying phase, but wood can change shape later, too.
4. VERTICAL GRAIN IS MORE STABLE
Inspecting the grain pattern on the end of a board will reveal whether the board has vertical grain or flat grain. A flat-grain board will move about twice as much as a vertical-grain board with the same change in moisture content. But because cutting quartersawn lumber is much less efficient, vertical-grain boards are expensive and can be hard to find.Quarter sawn and plain sawn wood
How a board is cut from the log also affects how much it moves. Quarter-sawing yields “vertical grain” boards, while plain-sawn boards have “flat grain.”