Wood movement is the movement of wood — shrinking and swelling — that occurs because wood absorbs and releases moisture. In a dry environment the wood releases moisture and shrinks; in a humid environment it absorbs moisture and expands. Because wood is a natural product that “breathes”, it keeps moving as long as it is in use, even after years.
How wood moves
Wood does not move equally in all directions:
- Along the length (grain direction) — hardly at all
- Radially (towards the core) — moderately
- Tangentially (along the growth rings) — the most
As a result a board can shrink or swell noticeably across its width, while the length stays practically the same. Wood can also warp if one side dries faster than the other.
Allowing for movement
- Let wood acclimatise — let it get used to the humidity of the room before working with it
- Work with the movement — leave room for shrinkage on wide boards, for example with tongue-and-groove or floating fixing
- Use dried wood — kiln-dried or dried to a suitable moisture content gives less after-movement
- Prevent one-sided moisture — a good finish on all sides keeps the moisture absorption even
Anyone who ignores movement gets cracks, gaps, sticking doors or joints that come loose.
Related terms
- Timber
- Wood species
- Shrinkage
- Hygroscopic
- Timber joints
- Tongue and groove
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