More questions on drying slabs

[Seaman]

I hope this makes sense,

If I do a real good job stacking and stickering slabs ( 2-3in thick) to air dry, how low does the MC need to be to rule out any major future movement.
Thanks, frank

[WDH]

I would say below 20 - 25%.  That is going to take a good long while. 

[GeneWengert-WoodDoc]

As a general rule, wood shrinks about 1% in size for a 4% MC change.  So, what will be the final MC of the wood?  If used indoors, typically 7% MC.  In a house wall, 10-12% MC.  Outside protected from rain, 12% MC.  So, you want to get the thick pieces to within 2% MC of the final in-use MC to avoid much moisture change which means avoiding shrinking or swelling.  Wood does not shrink or swell unless its MC changes...temperature has no effect; it is just relative humidity that changes MC.

If you are going to cut these into smaller pieces, then the core MC of the large pieces is also important.

Ok?

[Seaman]

Thanks, makes sense.

[JohnM]

To piggyback on this a bit...  Is it 'ok' to kiln dry a slab, say 3" thick 4 feet wide?  (Not that I have a kiln nor have I yet to make a slab. : :D)  Was just curious if it's 'bad' to remove the moisture too quickly on something that size?

JM

[JohnM]

Thought of something else*.  Should stickers be wider/thicker (2x2?) when stacking the slabs for drying?

*I don't think I've ever been to this section before today. :-\  More info to absorb. : ;D

[WDH]

The thicker the piece, the slower the drying to prevent splits, cracks, checks, honeycombing, etc.  Slabs have to dry very slowly.  I do not believe that the stickers need to be wider.  Regular sized stickers keep the humidity from the evaporating water high between the layers of slabs and this helps keep them from drying too fast.  Slabs are best dried in the company of other slabs.  Dried singly, without company in layers to keep the humidity up, a slab will tend to dry too fast and you will get the cracks, splits, checks, honeycomb, etc. 

[GeneWengert-WoodDoc]

I agree with WDH.  The reason for slower drying is that when there is a wider piece, the overall shrinkage is higher, so the stress in the center width-wise will be higher.  And of course, the thicker the piece, the slower it must be dried as well.

[JohnM]

   Thank you both.

[WDH]

I have stood some single slabs up against the wall under the lumber drying shed by themsleves.  They get lonely and split, check, and crack, bad.  They want the company of other slabs in a sticker stack.  Even 4/4 lumber above and below in layers will keep them company. 

[GeneWengert-WoodDoc]

WDH marks a good point.  All wood dries because of the temperature, RH and air flow...in a kiln, an air yard, a shop, etc.

[Sawmill Man]

What would be the ideal temperature and RH to dry these thick slabs with minimum defect?

[5quarter]

I have dried wide, thick slabs in both a conventional stickered stack and vertically like dominos. For a reason that is still a mystery to me, The vertically dried slabs tend to dry with much less defect. Typically, when setting up a set of slabs, I lean the worst one against the wall nearly vertical. I set the next one against the first, separated by a ¾" sticker on top and bottom. This is in a mostly enclosed, unheated machine shed. airflow is minimal but even. Which reminds me...Whether stacking vertical or horizontal, all air drying should have the same volume of air flow between the layers. That is, any board or slab that gets restricted airflow on one side only will twist itself around and walk off on you.  Heavy oak (8/4 or better) is especially tough to dry without defect. Even the best kiln operators bring their "A" game for those loads. I have some 9/4 bur oak planks that I'm drying right now. I keep the air flow severely restricted. I also make a habit of cutting thicker oak in the fall. By the following May, the core is still ~35%, but the greatest risk of defect is largely passed.

Sawmill man...Different woods will have different ideal drying environments (schedules). maybe Gene can give a few examples. Member Ironwood has a quick and dirty method for drying slabs involving fire and an old propane tank. Do not attempt without adult supervision.  ;) :D

[Jim_Rogers]

I'd be interested in learning Ironwood's method of drying wide or thick slabs....

Jim Rogers

[giant splinter]

I have had fairly good luck drying beams and lumber, generally have them cut, stickered and stacked in plenty of time to allow them to air dry in a fairly small area under movable sections of roof structure before I need to use them, lift off the roof and load out the material .. I would like to have a nice covered drying area around 30.0'X 50.0' to keep them completely out of the weather, driven rain or drifting snow seem to get the stacks slightly wet at times and tarps don't really make a big difference as in bad weather some moisture finds its way under a tarp.
So far its been working out fairly well with a cheap moisture meter, I know its not accurate but for what I do its working ok.

[Den Socling]

 

 

It's too bad that vac kilns are so thumping expensive. Here's a 4" thick x 40" wide Black Walnut slab that I dried in 33 days.

[YellowHammer]

Wow  - pretty much says it all!
YH

[C_Miller]

did some experimenting had 3 1/2 " soft maple slabs and 5/4 quartersawn oak. maple was a freebie and oak was for money.  stacked a layer of maple then a layer of oak. this kept the airflow fairly consistent and then dried using the oak schedule.  all said and done maple went from 70-30%  and oak went from 65 - 6% in 4 weeks.

[Den Socling]

This sounds odd. I would have expected the maple to be dry.

[GeneWengert-WoodDoc]

Even though maple dries faster than oak, the fact that it was three times thicker means it will dry slower....much slower.