I currently have a mixed load I'd like to dry. Itís the same species but a combination of 4/4 and 8/4. I'm running a dehumidification kiln. How would it work to double stack the 4/4 (two pieces together without a spacer) to make it the same relative thickness as the 8/4 lumber? Would both the 8/4 and the double stacked 4/4 dry at close to the same rate without a lot of degrade?
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Do not double stack. The reason is that the core will always be a little bit different than the shell, so with the 4/4 pieces, you will have a gradient, face to face, and that means warping after drying. It tales 2.5 times longer to dry 8/4 than 4/4.
You should consider shed drying the 8/4 and that will shorten the drying time. You can also shed dry the 4/4. With shed drying, you can still not mix, but drying will be fast enough that you can do two separate loads.