Gene Wengert, wooddoc@uwalumni.com
Casehardening occurs when the outside tries to shrink, but can't because of the wet core.
A: What you are seeing is called casehardening or drying stress. It occurs because at the beginning of drying, the outside tried to shrink, but could not because of the wet core. So, the outside dried to a larger shape than if it had been free to shrink. This creates a stress condition that, when the pieces are ripped, will cause the pieces to bow; the left piece will be a mirror image of the warp in the right piece. (Sometimes there is stress in the tree and this stress will cause immediate warp but it will not be balanced, left to right.) It is not uncommon that construction lumber will have casehardening; it does not hurt anyone and would cost money to remove during drying. Casehardening does not affect nailing as it is a stress condition so nothing is harder.
So, how do you remove casehardening? Existing casehardening is removed by steaming the material for a few hours. (Water misting might work too.) As you only need a few pieces to be stress free, I wonder if you can find someone with a steamer for cleaning car engines, etc. or a rental place where you can borrow a steamer when needed?
Gene Wengert, "The Wood Doctor," has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.
Updated: Oct 30, 2012
This article appeared in CabinetMakerFDM, February 2011. ©Copyright 2013, All Rights Reserved.