The drying process is fairly straightforward, yet many lumber suppliers are willing to cut corners in order to respond to customer demands for less expensive lumber. Improperly dried lumber usually isn’t easy to identify until after installation — and that’s never a good thing. So how can you be sure that the lumber you purchase won’t end up revealing problematic drying? Simply asking whether it’s kiln dried may not be enough.
Kiln Dried Moisture Ranges
Did you know that European standards for kiln-dried material can be up to 7% wetter than North American standards? For interior work, that’s a really big deal! This issue comes into play particularly when dealing with exotic species that are typically dried to European standards. African and European species such as African Mahogany, Sapele, Utile, Wenge, and others, typically arrive in our lumber yard already kiln dried, but to only between 12-15% moisture levels; in the United States and Canada, you really want the moisture level to range between 6-12%.
Quality Control Concerns
The first step to ensure proper moisture content is to take moisture level readings several places throughout a pack of lumber — including boards on the outer layer as well as in the middle of the pack. At J. Gibson McIlvain, we record those readings on a check-in sheet before the lumber is sent through our inventory system where it is accurately measured and counted. The lumber then gets moved to an air drying yard for an acclimation period. Even when the moisture readings reveal a wide range of moisture content levels in a pack, this air drying period can level the playing field.
Kiln Drying Concerns
Since so much of the lumber we receive has already been kiln dried to European standards, it’s important to note that the greatest benefit of kiln drying — setting the lignin between the cell walls — occurs once the moisture levels decrease to less than 8%. Since European standards allow more moisture than that, the longer the lumber has been out of those kilns, the more moisture it can actually absorb. Once a board is kiln dried to North American standards, though, it will no longer shed and soak up moisture as quickly, thus minimizing the risk of future dramatic movement.
At the end of the day, quality control in the drying process will provide you with a durable product that withstands both the installation process and years of seasonal moisture level shifts. At the same time, a careful approach to drying will cost you more time and money than poorer quality counterparts. Make sure the imported lumber you purchase has not only been kiln dried but also re-dried to North American standards. Feel free to ask them about their quality control and drying process, in general, to make sure you’re getting the kind of quality product your hard work requires.