The moisture content should be 6 to 8 percent.
If this lumber is 8/4 or thicker, it could still be wet in the inner most parts. Usually, air drying is planned on 1" per year. So, be careful about bringing it into your shop too soon. If it's 1", it should be down to the average outside RH of your area. This is different than inside RH and should probably be kiln dried.
"The Soul of a Tree" by George Nakajima is a great book. He made beautiful furniture, all from air dried wood. He said kilning wood, particularly steam kilning, make the wood seem dead, and changed its color.
All wood moves, no matter how it is dried, but air-dried moves more to get to the equilibrium point. With flat sawn wood, the closer to the heart, the more it will cup when it dries out. Quartersawn cups much less, but does take a little longer to dry.
Some articles mention that George Nakashima's wood was air dried, then kiln dried. In any case, he allowed the wood to stabilize for years, sometimes decades, before using it. Also, he understood how wood moves and his furniture was made to withstand seasonal changes without undue stresses caused by anchoring cross-grain to long grain boards.
The old musical instruments were made in a heated shop with lumber stored in the rafters. Although it was air dried, it then dried further in the shop. Additionally, without central heating, the 6 to7% MC (not 6 to 8% MC) that is best today for flatsawn oak (quartersawn shrinks less and most other species shrink less) is not necessary, as the EMC was higher (and in Europe it still is higher). Central heated locations in the US require lower MCs.
What are you making? If it is a chair leg and it shrinks, so what? It becomes a little smaller and maybe the end shrinks so it does not fit the hole well, but that is often okay, depending on the style of fastener. The holes for the stretchers will shrink and that is good. A tabletop that warps (especially one with a center joint and leaf) requires very close MC control. A floor that will be without cracks needs close MC control. So does a large door. Cabinet doors are also sensitive.
I consult with the wood industry weekly on corrections and trouble shooting for MC problems (among other things). Anyone who thinks that wood over 8% MC (often over 7% MC) can be used has a special case or narrow perspective on this industry.
Gene Wengert, forum technical advisor
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