Have you ever wondered how hardwood lumber is dried in preparation for manufacturing? For most consumer products and applications hardwood lumber needs to be dried prior to use.
The process of developing hardwood boards begins at the sawmill. In a sawmill is where the process of cutting round hardwood logs into flat hardwood boards is done. At that stage, the boards cut are considered to be green. This means the boards are still full of the moisture that was present in the tree while it was standing. If the boards are used at this time in manufacturing they will shrink, distort and change dimensions as the moisture naturally is released overtime. That is why hardwood manufactures, or companies who operate their own kilns, will go through the process of drying their hardwood lumber.
To dry hardwood boards, manufacturers will usually use a combination of air drying and kiln drying hardwood lumber. Air-drying or pre-drying techniques are used to help make the kiln drying process more efficient. The exact process depends on the species, thicknesses of lumber, time allotted and several more factors. During this process the goal is typically to get the lumber to a moisture content of around 30-40%. There are limitations and issues to deal with in both practices such as climate, the general exposure to weather and time which have a significant impact on the lumber. For example, cold weather increases the time to dry and exceptionally hot and dry weather could severely degrade the boards while drying such as surface checking or end splitting. So this process is very much an art and subject to many different factors and practices.
Kiln drying is more regulated. During this stage the lumber is placed on sticks, loaded into a large industrial oven and slowly treated with heat to remove additional moisture from the boards. The time a load of lumber stays in the kiln varies greatly and depends on factor such as species, thickness, time of year, and more. Ultimately, the lumber is kiln dried down to a moisture content of 12% or less in most regions. That is when hardwood lumber is usually considered to be acceptable for commercial use.
If you are looking for more information, or to better understand how we leverage both practices when we dry hardwood lumber, be sure to contact your American Lumber sales representative.