ENCYCLOPEDIA OF WOOD

DRYING AND. STORING WOOD

Wood is by nature a hygroscopic material: It absorbs and releas­es moisture depending on the humidity of the air around it. As wood soaks up moisture, it swells; when it expels mois­ture, the wood shrinks. These simple truths have significant impact on every piece of furniture you build. For exam­ple, your joinery methods should allow for wood movement. If they do not, pieces of furniture can literally self - destruct. While the application of a wood finish may slow dimensional change, nothing can stop it.

Freshly cut lumber, or green wood, has a relatively high moisture content, which for hardwoods can range from 60 percent to 100 percent of the dry weight.

This chapter focuses on ways of reduc­ing that to a level suitable for cabinetmaking, around 8 to 10 percent, depending on the climate and species.

Unless you buy green wood with the intention of drying it yourself, your lumber is already either air-dried or kiln-dried. Air-dried wood may have up to 25 percent moisture con­tent. Kiln-dried lumber has a lower level, 6 to 8 percent. Although kiln-dried wood is generally preferable for furni­ture building, some purists avoid it, contending that the process subdues the natural colors of certain woods and, in the short term, can induce internal stresses in the wood, making it difficult to resaw.

Large industrial kilns house hundreds of planks at a time, but there are a number of do-it-yourself models that are rela­tively simple to built, including a small-scale solar-powered
kiln that will enable you to dry green lumber in your backyard (page 84).

Air-drying wood is an equally worth­while option for seasoning certain species of green lumber, provided the wood is properly stacked, stickered and covered. Stickers are small boards that separate layers of lumber in a pile, allow­ing air circulation around the individ­ual planks. For a species like Eastern white pine, air-drying to a 10 to 12 per­cent moisture level is sufficient for most furniture projects. Whichever drying method you choose, you can use a spe­cial meter like the one shown in the pho­to above to measure moisture content.

Apart from control over the wood, the principal benefit of drying lumber in the shop is economic. The fewer oper­ations performed on a plank before you buy it—such as dry­ing and surfacing—the less it costs. For large quantities of lumber—say, 1,000 board feet or more—the savings can add up to hundreds of dollars.

Proper storage is as important as drying. Dried wood exposed to the elements can re-absorb some of the moisture that was extracted from it. There are several ways to store wood, depending on the kind of space you have and the wood you work with—from long planks to short stock too precious to be consigned to the kindling box. You can design your own lum­ber rack, using the ones shown in this chapter as starting points, or install a commercial lumber rack. If you use your basement to store wood, consider installing a dehumidifier to reduce the high relative humidity level common in such an area.

Kilns provide a fast and effective way of drying wood to a moisture level appropriate for cabi­netmaking. Here, stacks of hardwood planks are loaded by forklift into an industrial kiln.