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Conditioning is the process of adding moisture quickly and at higher temperatures to the surface or shell of lumber to cause the surface to try and expand, which (because it cannot expand) creates stress that cancels or offsets the casehardening stress, which was caused by attempted shrinkage early in drying. (Sometimes, conditioning is the term used for equalization...not a correct use.)The prong test is used to measure casehardening, but it requires no moisture gradient within the piece of lumber in order to be accurate. That is why putting it a microwave for 30 seconds or so after cutting, will help create uniform MC. It is likely that varying moisture at the end of drying means that equalization has not been done, so the prong test will not work.Note that when air drying, the high humidity every morning relieves the stress put in the previous day, so there is no casehardening stress, or need to condition, WITH WELL AIR DRIED LUMBER. This is why some people report putting a small amount of water on the floor relieves stress...there was no casehardening stress in the first place.
There are ways to overcome these obstacles, but different approaches for different problems
I agree with Scott, great post Robert.Scott, do you have any way of tracking how much water your are adding with your system. I'm curious?
What kiln system are you running Scott?
Walnut, on the other hand, has a very high allowable moisture release rate, leading one to believe that removing moisture from it will be easy, like poplar. However, due to many reasons, walnut is one of the most ill behaved wood in a low temp DH kiln, and frequently "locks up" during the drying process, sometimes having huge moisture gradients in boards. I've had it as high as 18% MC in one board and the board next to it in the pack be at 7%. Add the fact that walnut is usually is very internally stressed wood to begin with, then thats why it is such a pain to dry correctly, get a low moisture gradient, get it done in a reasonable time, and have straight boards. Walnut is a pain.
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