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Wood drying (also seasoning lumber or wood seasoning) reduces the moisture content of wood before its use. When the drying is done in a kiln , the product is known as kiln-dried timber or lumber , whereas air drying is the more traditional method.
Wood is normally dried to a point where it is in equilibrium with the atmospheric moisture content or relative humidity, and since this varies so does the equilibrium moisture content. Laboratory testing has found the average FSP in many types of wood to be approximately 26%. Individual species may differ from the average. [2]
The Thermo wood process consists of drying, heat treatment and finally cooling/conditioning, and takes up to 72 hours. [4] The Plato process consists of hydrothermolysis, dry curing and conditioning, and can take up to 7 days. The required time depends on wood species, width and initial moisture content. [5]
Green wood contains more moisture than seasoned wood, which has been dried through passage of time or by forced drying in kilns. Green wood is considered to have 100% moisture content relative to air-dried or seasoned wood, which is considered to be 20%.
In North America, logs reach equilibrium moisture content at about 6% and 12%; [8] since most kiln-dried logs are dried down to about 18% to 20% moisture content, kiln-dried logs can be expected to shrink and settle over time, but to a lesser extent than green logs.
However, in the 1980s, the development of chemical treatment processes allowed the wood to be more widely used for furniture making and frames. Rubberwood is generally treated soon after sawing by pressurized immersion in boron preservative solution to diffuse the chemicals. Then, the treated timber is kiln-dried to reduce its moisture content ...
Green wood coming straight from the felled tree has far too high a moisture content to be commercially useful and will rot, warp and split. Both hardwoods and softwood must be left to dry out until the moisture content is between 18% and 8%. This can be a long process unless accelerated by use of a kiln.
A moisture meter gives a reading of the approximate moisture content of wood. The reading helps in determining whether the wood is suitably dry for its intended purpose. The moisture content reading can also assist in planning a project design that will accommodate future changes in dimension caused by changes in relative humidity.