For any lumber species, effectively drying the wood requires a long and slow process of gradually heating it up and cooling it down. However, the maximum temperature and heating and cooling rates vary according to species. As a result, many kiln operators use published species-specific schedules as guides while developing their own systems through personal experience. As you might expect, thicker lumber has traditionally been difficult to thoroughly dry without damaging the wood in significant ways. This long-time problem is finally being solved, thanks to new radio frequency (RF) vacuum kiln technology.
Because thicker timbers take longer to dry, checking and cracking can easily result. As the outer layers dry, they function as shields that keep the interior layers from drying properly. Continued heating or raised temperatures can result in damage to those outer fibers or even breakage and separation in the moist inner core, producing what’s called “honeycomb lumber.” One solution is to dry the timbers until 2” of depth is dried, leaving the core with a 15-20% moisture range. That scenario allows the outer dry fibers to stabilize the entire board. However, problems often occur when planing causes a reduction in thickness to that dry outer shell, potentially exposing the moist inner fibers. Cross-cutting also creates the potential for checking.
One of our suppliers has come up with a new drying method that completely eliminates those problems. The patented RF vacuum kiln produces 100% dry timbers without damage to the fibers of the wood. The resulting lumber is comparable to air dried lumber, without damage to the cell wall or difficulties in workability. This two-fold process includes kiln-drying and radio frequency heating.
In the first part of the process, the lumber is loaded into the kiln. Once inside the kiln, the pressure is dropped, lowering the boiling point of the water inside the lumber to 90 degrees F. This drop in boiling point eliminates the potential for damage to the outer wood fibers. A constant vacuum of air pulls the water out of the lumber through the end grain, the way it circulated into the tree during its lifetime, further preventing damage to the cell wall.
In the second part of the process, radio frequency waves are used to heat the lumber. The vibration of air causes its temperature to rise as the molecules bounce around. Since radio waves penetrate a solid and cause the air to heat in a uniform manner throughout it, the inside of the board is heated at the same rate as the exterior layers of wood. Because the moisture is boiling off every part of the wood at the same rate, there’s no issue with checking. Because the timbers are truly dry throughout, the product is called “Tru-Dry.”
J. Gibson McIlvain Lumber Company
J. Gibson McIlvain is happy to make True-Dry timber available in Douglas Fir. We can also supply it through special order in Western Red Cedar and White Oak. As more species become available, we’ll be pleased to offer them to our valued customers, as well. Order some today by calling (800) 638-9100 to speak with a regional J. Gibson McIlvain representative or visit our website at www.mcilvain.com. We ship throughout the contiguous United States as well as to Alaska, Hawaii and the Caribbean Islands.