Words matter. Use your words. As helpful as those reminders may be, some words may not be as helpful as we think they are. When people define terms differently than one another, miscommunication is often the result. In the lumber industry, the term “kiln-dried lumber” can be one of those terms. Based on what you learned in Part 1, in addition to using that term, you may want to ask questions about what moisture level the lumber was kiln-dried to or specify the end moisture level you desire.
How We Proceed in the Air-Drying Process
When exotic lumber arrives in our lumber yard, our practice is to take moisture readings at multiple locations throughout the pack; we don’t want to measure only the outer layer but also boards buried in the center of the pack. The 3 unique readings are then documented on a form and sent through our Vision Tally System, which allows us to keep extremely accurate and detailed records of our inventory. After that, the lumber heads to our air-drying yards in order to undergo a standard acclimatization process.
This air-drying step helps lumber recover from the difficult journey it’s taken inside shipping containers, which is one more factor that undeniably affects the moisture content of the lumber. We stack the lumber on blocks with stickers inserted to promote airflow, allowing the lumber to come into equilibrium with our North American East Coast climate. The significance of those few weeks of allowing the lumber to acclimate cannot be overestimated. Not only will this timeframe allow the moisture levels of each board to even out, no matter where the board was located in the pack, but it will also promote a lower moisture level overall, since our local climate is drier than the origin of most exotic lumber – or the shipping container in which it made its overseas voyage.
We carefully determine the amount of time we allocate for this air-drying process based on the lumber species and its moisture content when it arrived in our yard. We realize that rushing lumber into the kiln can lead to instability, so we don’t skimp on the time we take.
What Happens During the Kiln-Drying Process
With lumber that has previously been subjected to the kiln-drying process, we realize that during the process, the cell walls have already been hardened, positively impacting its stability. At the same time, those cells will become more significantly hardened, and the lumber stable, once the lumber’s moisture content is further reduced to less than 8%. Typically, when lumber exits our kilns, it will begin to take on moisture in keeping with our climate; however, we realize that taking the moisture level down to the level where the cell walls will be set is a significant benefit, allowing for slower shedding and absorption of moisture, preventing cracking and other types of damage.
While you will see the cost of careful re-drying reflected in your bottom line, the kind of quality control that includes these important steps will pay dividends in the form of stable, high-quality lumber.