Why does wood move?
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 can exert a tremendous force that is almost unstoppable. But with a little knowledge of wood movement, you can minimise its potential consequences. Here we will explain the basics of wood movement and show you real-world solutions to the problems that it can cause.
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 150mm wide during a humid summer might shrink by nearly 0.8mm in winter. That’s not much, but it’s enough to cause a crack in a tabletop or create gaps between floorboards.
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 exactly the same.