Air-drying lumber is more than a matter of time

Q:

A friend cut down two cherry trees, and I agreed to haul them away in exchange for the lumber. How long do I need to air-dry the wood before I can use it for furnituremaking?     
—Travis Woods, Mount Vernon, Va.

A:

In general, Travis, air-drying green lumber reduces boards’ moisture content (the ratio of the weight of the water in the wood to the weight of dry wood) to about 15-20 percent. This  can take anywhere from six weeks to years, depending on the species, thickness, and local conditions. 

Even then, you’ll need to let the lumber continue drying for several more weeks or months in a space with a climate similar to where the finished piece will rest. So instead of a clock or calendar, rely on a moisture meter, available from woodworking suppliers, to determine readiness. 

First things first

Mill the logs into boards, ideally no more than 2" thick and 12" wide—thicker boards take longer to air-dry. Seal the ends by brushing on a commercial end-sealer, latex paint, or wax to slow the escape of moisture  through the end grain and minimize end splitting. At this point, the moisture content can easily exceed 100 percent.

Stack the boards as shown below with stickers between the layers to allow free airflow through the stack. Cut uniform stickers from dried hardwood such as poplar or soft maple. After stacking the boards, just leave it to nature, taking periodic meter readings until the moisture content stabilizes. 

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Stacking boards properly is the key to air-drying success. Build your drying stack outdoors or indoors (indoor drying will take longer), keeping the boards well off the ground, level, uniform, and fully supported.

Using your lumber

Wood is hygroscopic—it constantly gives up and absorbs moisture to reach equilibrium with the surrounding environment, which can be in the single digits. Stock that is air-dried outdoors usually will have higher moisture content than the indoor humidity. 

Avoid wood-movement problems with indoor projects by acclimating the wood to the inside conditions before building with it. Stack the lumber where conditions match its end use and test it with your meter until the moisture content stabilizes.

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