Which is Best? Kiln Dried vs. Air Dried Logs

Frequently, we are asked which is best: air-dried or kiln-dried logs? And the debate has been ongoing for a long time. Actually, each drying process has its advantages.

Air-dried logs are usually dried naturally by being left outside and exposed to the weather. An ideal location would be where logs are subjected to the sun and wind, usually high on a hill. This generally takes a minimum of 12 months under optimum conditions. The goal is to reduce the moisture content (M.C.) to about 25% or less. This will vary somewhat depending on the species. For instance, Northern White Cedar dries faster then Eastern White Pine. The manufacture is also at the mercy of the weather and the climate that they may be in.

The slower the wood drys the less checking normally occurs. Thus, the assumption that air-dried will have less checking. However, in a controlled environment like inside today’s new modern kilns where automatic “misting” can add moisture as needed (providing the operator is competent), little difference should be noticed. Air- dried may settle more, depending on the moisture content, then kiln- dried though since it usually has a higher M.C. Air-dried logs are less expensive, up to 20% less, then kiln-dried since the substantial investment and the high cost of running the kiln is eliminated.

Kiln-drying is the most effective way of ridding logs and timbers of mold, mildew and insect infestation. The kiln is turned up to 150 degrees on the final days of drying, which kills larvae and insects. Kiln-drying also “sets the pitch,” which means the sap is crystallized and will not seep out later. Kiln-dried material is periodically checked during the drying process until the M.C. reaches the desired level. When the manufacture kiln-dries the logs down to an average of 18%-19%, they will settle very little, as low as 1/2” for a 8’ wall.

Dr. Gene Wengerd, Ph.D of Wood Doctor’s Rx, LLC, says, “kiln-dried logs and timber are better than air-dried products as the moisture content is lower in kiln dried material which means, in turn, that most of the natural shrinkage that will occur in wood as it dries will occur during the drying process rather than after installation. As a result they will be more stable - requiring less caulking and less problems, like doors and windows sticking.” Other benefits he says is “the material is 10 to 20% lighter than air-dried and 50% lighter than green logs and that the logs are sanitized from mold, mildew, stain fungi and decay fungi (which cause rot), plus insects, their larvae and

eggs, are all killed when temperatures exceed 130°F. Furthermore, as these pathogens require water for their daily activity, the drying also eliminates the required moister.” He also stated that “when wood is heated over 150°F in the kiln, the sap, pitch or resin in the wood that would be liquid

at room temperatures is evaporated. The likelihood of seepage of sap after installation is virtually eliminated.” Another point he made, is that “kiln dried wood is ready for the application of the finish, and that in many cases, the finish itself will penetrate deeper with kiln-dried wood, providing longer lasting finishes.”

Hochstetler has a unique, 2-step method of drying. Cants (square timbers which will be milled into logs) are air-dried for up to 9 months and then taken to our kiln to be “finished off.” This normally takes an additional 10 days or so (depending on the moisture content), until cants reach an average of 18%-19%. Having our own modern kilns (verses in the old days where we depended on others to kiln-dry our wood) has given us the quality control that is so important in proper kiln drying.

Using this 2-step method gives our clients the best of both worlds. First, with the slow drying of air-drying you get minimum checking. Plus, with the kiln-drying you get the benefit of a dryer, sanitized, stable log that doesn’t seep sap.