What are Kiln Dried Logs?

Heather Phillips

Kiln dried logs are pieces of wood that have been have been carefully dried by extracting moisture from them with the use of heat and air. They are typically much more structurally stable than green wood. Consequently, they are not as prone to shrinkage, expansion, and checking. They are also generally rendered free of insect pests and fungi. Also, the pitch in kiln dried logs crystallizes, making the wood less likely to seep it and become sticky later.

Kilns in lumber yards dry logs.
Kilns in lumber yards dry logs.

For many reasons, such timber is often used in the construction of log homes. The wood usually has minimal shrinkage, since excess water has been removed. In addition, kiln dried lumber tends to be less susceptible to warping. It is also lighter and thus easier to handle, because of its reduced moisture content. Further, its surface will typically better accept stains and other finishes.

Kiln dried logs are free of insect pests.
Kiln dried logs are free of insect pests.

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The practice of kiln-drying wood generally occurs over a period of weeks. Four to six weeks is not an unusual amount of time for kiln dried logs to be processed. The amount of time is determined by species of tree — hardwoods generally take longer than softwoods — and moisture content. Ideal moisture is determined by the geographic location where it will be used. For instance, typical moisture content ranges for most of Australia are in the 10 to 20% range.

To dry logs, lumber kilns can be configured in any number of ways. Generally, they are powered by natural gas, electricity, or oil. They can also make use of steam heat or be solar-powered. The temperature inside a kiln is raised slowly to approximately 170°F (76.67°C). This heated air speeds up moisture evaporation from the logs. Large fans usually circulate the air, and dehumidifiers remove moisture.

Kiln dried logs are carefully monitored during the drying process because their exteriors tend to dry faster than the inside. If the wood is dried too rapidly, it can be ruined due to severe checking and cracking. To prevent this from happening, steam is often applied to equalize the moisture content of the outside portion of the log, with its interior.

Sometimes kiln dried logs are used for firewood. They have the advantage of burning cleaner than wood, with a higher moisture content. Since, the wood has also been sanitized by the heat of the kiln and is free of pests, it is desirable for use in indoor fireplaces or woodstoves.

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