What Can Go Wrong With the Drying Process of Kiln Dried Wood?

Checks and Splits

• The drying process produces a lot of stress against the wood fibers. As drying begins, the outside wood fibers dry faster than the internal fibers. As a result, the internal fibers become compressed by the outside fibers. Checks occur when the external wood fibers separate against the lumber's natural grain, or across the growth rings. In contrast, splits are external wood fiber separations along the lumber's grain. Drying stress causes both breakages to occur if the kiln's drying temperature is not varied. Typically, the kiln's temperature begins at approximately 110 degrees Fahrenheit. As the wood dries, the temperature is systematically increased to about 170 to 180 degrees Fahrenheit. This temperature variation prevents wood damage during manufacturing.

Honeycombing

• Honeycombing is check damage on the wood's interior fibers. Honeycombing occurs during the final drying stages. Wood that is heated for an extended amount of time will generate tension, or stretching, of the internal wood fibers. Internal fibers begin to separate against the wood grain, causing structural weakening without a visual external clue.

Casehardening

• Casehardening is essentially the opposite of honeycombing. External wood fibers become tensile, causing the wood to warp. Warping can cause the wood to have visual curves and twists to its wood fiber lengths. This warping tendency with casehardening compromises the wood's structural integrity.

Energy Considerations

• Sawmills must use the majority of their energy use toward physical wood drying. Regardless if the kiln drying process uses gas or electricity for generating a dry wood product, approximately 80 percent of a sawmill's energy use is for kiln applications, reports the University of Kentucky. Sawmills must commit to a large energy output or the drying process cannot be completed correctly, resulting in poor final wood quality reflecting cracks and warping.