Difference Between Air Dried and Kiln Dried Logs

Irrespective of the wood species you select to build your log home with, it starts with a freshly cut tree that contain high moisture content. Freshly sawn ‘Green’ logs look and feel wet. For wood to be ready to be used, it needs time to dry out so that it is stable in size and grade. As a natural process wood shrinks when the moisture content lowers. Hardwood can either be “Air Dried,” “Kiln Dried,” or “Green.” It is common practice to either air dry or use kiln drying in order to get the wood ready for use in the marketplace.

Read on to learn about both the processes of Air Drying and Kiln Drying.

Air Drying – Logs are graded and sorted for the natural process of drying in the open air by stacking them with spacers between each. Logs are left to dry in the open with cover overhead for a period of time, which can range from 8-16 months depending on the species.  Logs are air dried before the milling process to give it shape. Air drying allows the wood to naturally dry out the log evenly and with minimal natural cracking. Given time, the moisture content in the wood adjusts to the environment it is in to reach Equilibrium Moisture Content, wherein the wood neither gains nor loses moisture.

Benefits of Air Drying Logs

Air Drying Wood is said to have certain advantages over kiln-drying-

With air-dried wood there are no internal tensions baked into the wood.

Kiln dried wood can be more fragile and break off easily. It can chip easily especially when working with hand tools, spokeshave or powered knife.

Kiln dried wood often loses about 20% of its color, even when it is not steamed. The high temperature of the kiln kills some of the subtler colors of the wood grain.

Kiln dried lumber needs to be kept in a fully climate-controlled environment once it comes out of the kiln, because it reabsorbs moisture from the air. It returns to its previous air-dried state, while the brittle quality, internal tensions, and lack of color remain.

Kiln Drying – Kiln drying is a “forced” process, where logs are placed into a kiln and heat is applied by raising the temperature slowly to 170°F. The moisture is forced out from the wood more rapidly as large fans circulate the heated air throughout the kiln to help maintain a consistent drying rate in the logs. Dehumidifiers are used to remove the moisture-laden air from the kiln. At the end of this process, there will only be between 6-10% moisture content in the logs, and this is referred to as kiln dried. The drying rate has to be monitored so that the outside perimeters of larger diameter wood do not dry faster than the center. If left uncorrected, this imbalance causes shrinkage on the outside of the wood leading to severe checking or cracking. There are no regulations or guidelines for kiln drying within the log home industry.

Benefits of Kiln-Drying Logs

The advantages of kiln drying are the following –

The wood is usually heated to 170 F in a kiln, which ensures that all insects, eggs, bug larvae, mold and fungi in the wood get killed.

Virtually eliminates log shrinkage and minimize unwanted log checking or cracking

The heat in the kiln dries off the resin in resinous softwoods, which would otherwise be liquid and runny at room temperature.

There are no harsh chemical treatments needed for kiln-dried logs, as it sanitizes them.

Log strength increases as interior and exterior finishes can be applied immediately after construction, which penetrate deeper and is more longer-lasting in kiln-dried wood.

Kiln-dried wood is used for furniture, cabinets, flooring, and many other products, as it is less likely to cup and warp. This allows manufacturers to make a more durable product. Air dried lumber is preferred for outdoor patio furniture, fencing, and decking, while green lumber is used in the pallet industry.

You can call Performance Log Homes for advice on Air Dried -vs. – Kiln Dried logs. Call us at 800-781-2551 to find the log cabin building and restoration expertise you need. Get a beautiful log home that you can enjoy for years to come.