Whether it’s domestic or exotic lumber, locally harvested or imported, we essentially use the same mode of operation to get the moisture levels to where they need to be. Of course, depending on whether a given board is starting out at 35% or 15% moisture content will make a big difference in how long the process takes, which is something very difficult for those of us in this instant-gratification society of ours. But regardless of customer demands, J. Gibson McIlvain is committed to taking the time we need to ensure quality products, even if we don’t win any races.
Our lumber yards have back areas where air drying takes place, and pretty much all the lumber we receive spends at least some time in one of those back corners, sealed, stacked and stickered. Before they’re stacked, each board has its end sealed by being painted with wax; this sealing acts to slow the release of moisture from the straw-like wood fibers and prevent checking and cracking that might otherwise occur. Once they’re sealed, the boards are carefully stacked with spacers (called stickers) between each of them, allowing air to flow evenly on all sides of a board, in a method similar to how baked goods are more effectively cooled on cooling racks; instead of heat, however, it’s the moisture that’s able to be evenly released. The higher the moisture content of the wood when it arrives in our lumber yard, the longer it will have to spend in that back corner.
Unlike the case hardening that can occur during kiln drying, air drying provides a safe, gentle method of encouraging wood to shed extraneous moisture; depending on the wood species and its moisture content, the process can take a few weeks or many months. (Note that while some lumber suppliers boast that they have lumber that has been drying out for over a decade, drying lumber for years really won’t accomplish any more than the amount of weeks or months it takes the lumber to come into equilibrium with the local environment. Lumber drying out “for years” just means the lumber supplier has been struggling to sell that stack of lumber for a long period of time.)
Once the lumber has been air dried to an equilibrium with the environment, it’s ready for the kilns. J. Gibson McIlvain has 10 drying kilns, each of which is powered by a boiler heated by dust and offcuts generated in our mill. Depending on the species, we will set the kiln to a specific temperature and time in order to bring the lumber placed inside to within a 6 and 8% moisture content. While some species need to spend only a few weeks in the kiln, particularly dense species may need to spend more than a month in it.
Certain species, such as Spanish Cedar, require special handling due to issues with weeping. J. Gibson McIlvain has some of the only kilns in North America that get hot enough to allow the sap and resin from such species to set, keeping the weeping sap and resin from staining the lumber which would make it impossible to finish successfully. The higher temperatures, however, increase the chances of case hardening, making slow heat up and cool down periods even more important than usual.
Continue with Part 3.