As an organic material, wood is hygroscopic by nature. Imagine a bundle of straws, and you’ll have an understanding of the structure of lumber. The capillary action allows the wood to take in moisture, causing fibers to swell. The outcome is grain movement in the wood. Woodworking may be both exhilarating and frustrating owing to moisture absorption (causing wood swelling) and moisture loss (causing wood shrinkage) as a result of variable humidity conditions.
Movement of Wood
Understanding wood movement can help you avoid warping and cupping in the completed product, which can be frustrating. Without this understanding, your project plans can literally fall apart if they don’t initially take into consideration the reality of wood movement (whether shrinkage or swelling). Even while wood cannot be stopped from moving, it’s movement can be anticipated and accommodated to avoid catastrophic complications for your project. In fact, if you embrace the movement, you can use it to completely strengthen your joints.
Your job will be considerably easier if you start with adequately dried lumber. While dry wood will still move, it will do so in a more stable and predictable manner. Drying should take place over time in a regulated setting. The multi-step drying procedure produces lumber that is much more stable and has a lower chance of excessive movement.
Stability of Dry Lumber
Stable dried lumber can have varying moisture content depending on the climate. A typical moisture level of 6-8 percent for kiln-dried lumber makes sense for most of North America. Although the content may need to be increased in some locations, properly kiln-dried lumber will be close to this criterion. The European standard is higher, at 12-15 percent moisture content, due to a generally wetter climate. In addition to reaching these standard moisture levels, properly kiln-dried lumber hardens the lignin and ensures its retention. The cell walls will be less flexible as a result of this process, limiting the amount of movement available.
Rapid Drying = Precarious Stability
The stability that can be produced by setting the lignin can be lost when kiln drying is done too quickly, though. Because the outside layers dry faster than the interior layers, the outer layer may form a hard shell around the inside layers, keeping moisture inside. The upshot of this scenario, known as “hardening,” is unstable wood that moves dramatically when it is cut. Hardening is indicated by cracking and notable color changes.
There should be no excuse for badly dried lumber when drying schedules for certain species are widely available. When there is a supply-demand mismatch, however, the desire to expedite the drying process can trump a supplier’s common sense. Skipping industry accepted processes may help you get your product to market faster, but it won’t give you the best long-term outcomes. J. Gibson McIlvain understands the ramifications of rushing a project; however, we’d rather keep our reputation of providing only the highest-quality materials than fill an order with inferior lumber.
Continue reading with Part 2.