Replies

1. 
   wx2 | Apr 06, 2023 01:00pm | #1

   This situation is called “case hardening”. In the kiln drying process the slab did not dry evenly from the inside out or outside in, however you wish to look at it. The outer portion of the slab dried quickly and hardened. If you were to cut such a slab, unequal forces between the outside and the inside fibers would result in splitting of the slab. Such slabs are generally thought to be unusable.

1. 
   BillieRuben | Apr 06, 2023 09:57pm | #2

   Can you not just rough cut it to size and let it equalise for a good long while though? I don't really understand it.

   Especially cause that black tail guy sure loves his resin, so it's not like he couldn't fill cracks.

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   wx2 | Apr 07, 2023 12:39pm | #3

   I once tried to flatten a slab of Gary Oak. It looked quite good after the first pass. I left it overnight with plans to continue the next day. I was shocked upon seeing it in the morning. It was as though the whole surface had ruptured into the most unattractive cracks (think of a honey comb structure stretched out in one direction). There were as many voids as there was solid wood. One of the reasons that the Black Tail tables cost so much to buy is the large amount of epoxy that is used. Epoxy is not cheap! I do not know if a cased hardened slab would ever equilibrate enough over time. If it might, I anticipate it would be a VERY long time, and I doubt that many woodworkers would want to wait that long before getting started.

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   jfsksa | Apr 07, 2023 03:52pm | #4

   If my memory serves me, the moisture spots he pointed out were relatively small. They seemed to be only 4" or so across. I can't imagine that two or three of these in a big slab would cause stability issues.

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   MRM97330 | Apr 10, 2023 11:39pm | #5

   Walnut grown on the West Coast frequently has the wet streaks. It amazing. When it's pulled out of the kiln those small streaks still have the greenish tint of undried heartwood and you don't need a moisture meter. You can feel that they are wet. That they fracture relatively quickly might be explained by capillary forces. If they did not fracture, I suspect they would still be an issue. They would dry eventually, and the surface of the slab would have a small indentation due to shrinkage that would show, especially with a glossy finish.

   Western hemlock and white fir have a similar wet pocket problem. In these species, there is a sour odor that accompanies the wet pockets. It's bad enough that you can walk by the kiln and tell if there are a lot of wet pockets in the batch being dried.

   I don't want to offend anyone, but (like wx2 said) casehardening refers to a stress state in the wood after drying without conditioning (stress relief). Casehardening does not trap moisture, however. The permeability of the wood is not any different from stress-free wood. Nor is it any harder than wood of similar MC (another myth).

   This myth comes from other industries where the term is used for that purpose. For example, when spray-drying powders (like milk) a shell can form on the droplet if the temperature and relative humidity are not controlled properly. In that case, the dry shell on the droplet does hold in moisture.

   Casehardening will not "equilibrate" out over a reasonable amount of time. I tested a piece of unconditioned KD 5/4 red alder every year for over three years (so I would have a class demonstration) using the standard prong test used at kiln operations. There was very little difference from right out of the kiln to three years later. I did condition the rest of the kiln charge and there was no casehardening in other boards.

   Hope that helps.

1. 
   BillieRuben | Apr 12, 2023 04:24am | #6

   Dang! That's wild. I guess I just don't understand how it all works. Looks like I have some learning to do!