Drying / Kilning
The industry has extensive experience of drying hardwood lumber. In fact much of the research over the last 30 years related to drying temperate hardwood has emanated from the United States. Drying times will vary enormously depending on thickness and species. For example, 4/4" (25.4mm) tulipwood can be dried from green in 7-10 days, whereas 12/4" (76.2mm) white oak may take up to 8 months to kiln following an extensive period of air drying.
Economics dictate that in the majority of cases domestic and export lumber is kilned together. Therefore, export lumber will usually be dried to the domestic standard moisture content (MC) of 6-8%. Thicker material in some species may be up to 10-12% MC. Refractory drying species such as the oaks require air drying or controlled drying in pre-dryers prior to kilning to minimise degrade.
Other species such as aspen, cottonwood and hackberry are susceptible to blue staining and therefore require prompt kilning of fresh sawn material. Sticker stain or shadow can also be a problem with some species, notably hard maple. The American industry makes great efforts to minimise such problems where they are known to exist, by employing techniques such as conditioning schedules and profiled stickers.