Moisture’s Effect on Wood

Moisture in wood is an environmental issue and the effects on solid wood products are one of the most challenging realities in the cabinet industry. Solid wood products need stable moisture conditions to avoid potential problems like open joints, frame bowing, panel contraction or shrinking with exposed raw wood, cracking, warping/twists, sizing variations, and rail expanding beyond the stiles.

Not all woods will react the same way when they are exposed to moisture. To better understand the effects of moisture content with wood, we must realize that the properties of wood changes dramatically with changes in moisture content. The most noteworthy change is shrinking and swelling, especially in the width of the board. As you can see from the chart below, a Hard Maple door with a center panel of 18” wide will expand more than ¼” when the moisture content increases by 4%.

Moisture Effects on Wood Expansion & Contraction:

Panel Size 2% Change in Moisture Content 4% Change in Moisture Content 6% Change in Moisture Content
6” Wide Center Panel 1/16” 3/32” 1/8”
12” Wide Center Panel 3/32” 3/16” 1/4”
18” Wide Center Panel 1/8” 1/4” 3/8”
24” Wide Center Panel 3/16” 11/32” 1/2”
30” Wide Center Panel 7/32” 7/16” 5/8”
36” Wide Center Panel 1/4” 1/2” 3/4”

Moisture & Relative Humidity:

Wood is a hygroscopic (readily taking up and retaining moisture) material, meaning that it will continually trying to achieve an equilibrium condition with its environment. As the relative humidity changes, so does the moisture content of the wood. The following table shows the relationship between the relative humidity of the air and the moisture of the wood.

Relative Humidity of the Air Moisture Content of Wood
26-31% 6%
32 – 38% 7%
39-45% 8%

For woodworkers who build cabinets, fine furniture, and other wood products a normal range of wood moisture content should be between 6% – 8%.

The effects of moisture can be caused by the following:

  • Moisture-rich environments such as humid climates, water-front properties, coastal regions, non-air-conditioned locations, etc. are the most susceptible for expansion issues.
  • Dry climates are susceptible to products having contraction issues. This is most relevant during the winter months. Humidifiers are highly recommended to help prevent contraction issues.
  • Installation in new construction or renovations prior to proper climate controls will result in the product acclimating to the surrounding moisture conditions. The following products can release moisture into the residence during its curing/drying process: drywall compound, concrete, wood framing, incomplete plumbing and paints all release moisture into the environment.
  • The application of finish (clear topcoat or paint) does not prevent moisture exchange but can slow the process down.