Relationship between tension and kiln drying

[JoshNZ]

I've got a bunch of black walnut slabs back from a guy with a kiln which had a lot of tension in them, lots of splitting while cutting, boards lifting on opening cuts etc. I remember dropping the odd one and seeing slabs explode apart, trimming splits and seeing them propagate further etc.

The stuff I've got back seems to be happy as anything. I've trimmed splits off and they don't continue further, ripped them into lengths and seen no bending etc.

Is it necessary for timber to go through a kiln to achieve this? I can imagine the wood having been beaten up in a kiln will do all it's going to do, and be relaxed at the end. But it's only a theory. Would air drying for 2 years achieve the same result or is it this high heat and temperature change that does it?

[GeneWengert-WoodDoc]

Getting rid of growth stresses has been studied for a century with little progress.  The kiln does not help much at all.

[alan gage]

Getting rid of growth stresses has been studied for a century with little progress.  The kiln does not help much at all.

What about improper drying? Could it be the wood/slabs he got from the original kiln were dried improperly and made things worse?
Alan

[Ianab]

Could it be the wood/slabs he got from the original kiln were dried improperly and made things worse?

You could make things worse by case hardening the wood with incorrect drying, that causes all sorts weird things to happen.

[JoshNZ]

Not sure I'm following, the slabs were never worse than when they were fresh off the mill. The kiln made them a lot better it seems.

On the note if splitting @Ianab or any other kiwis what do you do for end sealer in NZ? I can't find anchorseal anywhere

[JoshNZ]

Yeah sorry I've worded my first post poorly. The trees are what had the tension, young walnut. Lots of carry on while milling. Splitting while handling or crosscutting. After the kiln run, aside from the existing splits it's been pretty good to work with

[WDH]

I have found small walnut and yellow poplar logs to the worst for growth stress.  

[YellowHammer]

Not sure I'm following, the slabs were never worse than when they were fresh off the mill. The kiln made them a lot better it seems.

This is why I will always let my walnut "stew" or "wilt" for an extra day at high temperatures, with a very slow cool down, no moisture removal, in the kiln.  It seems to settle them down a little.  It' subjective, but it produces less stressed wood for me.  The proof is when planing at the end.  A board with lots of internal stress will will bow, sometimes badly, when planed unequally from both sides.  Since we do a lot of facing, there is some unequal planing involved, and that's where I spot the problem.  Last night for example, I was double side carpet planing, and my cherry and walnut were coming out flat, but some professionally kiln dried maple I had bought would go in bowed and come out bowed in the other direction, indicating significant internal stress.

    

[alan gage]

Yeah sorry I've worded my first post poorly. The trees are what had the tension, young walnut. Lots of carry on while milling. Splitting while handling or crosscutting. After the kiln run, aside from the existing splits it's been pretty good to work with

Gotcha. The original post makes more sense to me now. I thought you'd gotten different results from different kiln driers.
Alan

[Ianab]

On the note if splitting @Ianab or any other kiwis what do you do for end sealer in NZ? I can't find anchorseal anywhere

Mobil used to sell a wax emulsion for the job, but I don't think the do any more. 
I did find this one though. 
End Grain Sealer (Log Shield ) 4 litre - Timberly Woodturning

[JoshNZ]

I think the kiln operator did the same thing here, must've had the same idea. He also left it sealed and let it cool over a couple of days.

I spotted that Ian, more or less the same stuff? I saw on u-buy a note under anchor seal saying this product is restricted in your country. Don't know if it was a website thing or what but kind of odd noone has bothered to stock it?

[Don P]

The world supply chain is a funny thing, y'all can get a structural rated polyurethane glue that I cannot buy here, even though it is made here, go figure. Foundation or roofing tar is a mess, especially if the wife leans back on some in her dress clothes! but it does work.

On topic, does steaming lessen the tension in walnut? I've experienced the same thing WDH mentioned, small poplar can finish the cut before the saw gets there  :D.

[JoshNZ]

Yeah I've run my saw down 1 slab after the opening cut on these walnut logs and just about had the edge cut me in half standing beside it the way it pops open. Definitely pays to pick your logs for slabbing. I do find there is rarely tension in the heart, if you're lucky enough to get rid of the sapwood without it pulling itself to bits then you're home free