The Science of Wood: Understanding Wood Movement

May 10

Wood is a versatile and beautiful material that has been used for centuries in a wide range of applications, from construction to furniture making. One of the key aspects of working with wood is understanding its inherent tendency to expand and contract, a phenomenon known as wood movement. In this in-depth guide, we'll explore the science behind wood movement, the factors that influence it, and how to accommodate for it in your woodworking projects to ensure longevity and durability.

Why Does Wood Move?

Wood is a natural, organic material composed of cellulose fibers held together by a matrix of lignin. As a hygroscopic material, wood absorbs and releases moisture from its surroundings, causing it to expand or contract. This dimensional change is what we refer to as wood movement.

Radial, Tangential, and Longitudinal Movement

Wood movement occurs along three primary axes:

Radial movement: Expansion and contraction in a direction perpendicular to the growth rings, typically the smallest amount of movement.
Tangential movement: Expansion and contraction in a direction parallel to the growth rings, usually the largest amount of movement.
Longitudinal movement: Expansion and contraction along the grain direction, typically minimal and often negligible in comparison to radial and tangential movement.

Understanding the differences between these types of movement is essential for predicting and managing wood movement in your projects.

Factors Affecting Wood Movement

Several factors can influence the extent and rate of wood movement:

Wood Species

Different wood species have varying levels of dimensional stability, with some being more prone to movement than others. When selecting wood for a project, it's essential to consider the species' stability, as well as its appearance and durability.

Moisture Content

Wood movement is directly related to the wood's moisture content, which is influenced by the relative humidity in the surrounding environment. As humidity increases, so does the moisture content of the wood, causing it to expand. Conversely, as humidity decreases, the wood dries out and contracts.

Grain Orientation

The grain orientation of a board can significantly impact its movement. For example, quartersawn lumber, where the growth rings are roughly perpendicular to the face of the board, is more dimensionally stable than flatsawn lumber, where the growth rings are more parallel to the face.

Accommodating Wood Movement in Your Projects

As a woodworker, it's crucial to anticipate and accommodate wood movement in your designs to avoid warping, splitting, or other structural issues. Here are some tips to help you manage wood movement in your projects:

Allow for Expansion and Contraction

When designing joinery or assembling furniture, allow for some movement by incorporating expansion gaps, sliding dovetails, or other flexible connections.

Choose Stable Wood Species

Select wood species that are known for their dimensional stability, such as quartersawn white oak or mahogany, to minimize movement in your projects.

Properly Dry and Acclimate Your Wood

Before using wood in your projects, ensure it has been properly dried to its equilibrium moisture content and acclimated to the environment where the finished piece will be placed.

Seal Wood Surfaces

Apply a finish to all wood surfaces to help slow down moisture exchange between the wood and its environment, reducing the rate of movement.

Understanding the science behind wood movement is crucial for creating long-lasting, durable woodworking projects. By choosing appropriate wood species, accounting for expansion and contraction, and properly drying and finishing your wood, you can minimize the impact of wood movement and ensure the success of your creations. Keep these factors in mind as you embark on your next woodworking endeavor, and stay tuned to the Colwood Craft blog for more tips, tricks, and insights into the world of woodworking.