Weighting lumber stacks.

[Dave Shepard]

How many forumites weigh down their lumber stacks? When the last batch of boards went into the quasikiln, the wide stuff ended up on top. It's all pine, and the wide stuff is 22". There is a lot of cupping across the width of the board. Would weighting the stacks make a difference? I put another stack in yesterday, and I put all the wide stuff on the bottom. I hate to see all my hard work shriveling up into a potato chip.


Dave

[Dan_Shade]

i weigh down my stuff.  80-100lbs per row of stickers.  It's a pain in the arse, but it helps keep the boards flat.

I use concrete weights.

[Tom]

The message I've gotten is that weight helps, but it's difficult to add enough weight to make any difference. 

What I've done is stack 2x material or even 6x6 on top of the stack.  My theory is that the weight helps, but it also puts the valuable 1x material below something that will slow the drying a bit.  sometimes it helps.

[Norm]

I do the same as Dan. On the top row I use concrete blocks to a double row of stickers. Still though some boards will move no matter how much weight you use. We have no softwoods here so my experience is in hardwoods.

[stonebroke]

I see that some people use cargo straps to maintain tension, at least on air dry piles. Don't know if it would work in a kiln.

Stonebroke

[Den Socling]

The conventional rule is 300 pounds per square foot.

I was having a problem with English elm warping in a vacuum kiln in Auckland. With the last load, I had the operator put the elm on the bottom and Sidney blue gum on top. That was enough weight.

If I am drying something really prone to warp like holly in a vacuum kiln, I lay a bladder on top and then leave in a little air into the bladder after I pull vacuum. Just 3psi gives me 432 pounds per square foot.

If you had a steel frame above your stack, I wonder if you could build an inflatable press with inner tubes?

[Dave Shepard]

That's a neat idea Den, thanks. The stacks are inside a shipping container. I am sure the roof would hold a lot of force. The only problem then would be integrating the fans. Although they haven't been bought yet. One step at a time, I guess. I like the air idea, you could put a pressure regulator on it and it would compensate for shrinkage.


Dave

[dundee]

I saw a 40 foot shipping container being used to dry Cypress pine in Australia only last week, this was not a vac kiln, what I did see, the owner bolted 6x6 on the width of the container roof the used hydraulic bottle jacks to create force onto the lumber, works fine with no warp /twist, the lumber was 150x27mm wide. These jacks were activated from a pump outside the container

This guy has dried 300mm pine boards the same way with OK results, the stickers were 300mm spacing of absolute / uniform thickness (of the same species)

[Don_Lewis]

I had one customer use two old water bed mattresses.

[OneWithWood]

I cover the stacks with plywood on stickers and then I put four rows of 2" limestone 14x14 pavers spaced evenly on the plywood.

I don't know if the weight helps, but it doesn't hurt and plywood/limestone gives me a nice flat surface for the baffles to rest on.

[zopi]

i've seen  6x bunks drilled to accept allthread...and matching ones on top..clamps the
boards down..dunno how well it works tho...but you can stack more lumber right on top..

[Kelvin]

My biggest timesaver was putting all my weight, anything, on pallets and putting 6x6's across the tin and setting the pallets, two per 8' length on top with forks.  Boy this works like a dream, course you gotta have a fork set, but man, can't imagine moving all that weight all the time.  I just stack a pallet with either bricks or log cut offs till my 2000# lift starts tipping and stick two of those on top.  Sure makes a difference.  I'd never leave lumber unweighted.  In the kiln i manually add bricks till i can't fit anymore on top.  this is a pain.  Someday i'll come up with something better there.

[solidwoods]

Sounds like the top may be over dry.
Or drying too fast.
have you checked that?
Pine if dried with dignity will dry flat.
jim

[Dave Shepard]

At the present time, we have little control over airflow and temperature. This pine was air dried outside for several months, but I did not get a starting MC before it went into the kiln.


Dave

[beenthere]

Dave
I'm wondering how the kiln operator can set up a dry kiln, not knowing what the moisture content is to start with??  Will the sample boards and moisture samples be a bit worthless under these conditions? 

Just curious, but how does one know when to take the lumber out of the kiln? 

Or just set up a Relative Humidity condition in the kiln that will give a dry moisture content like say, 8% mc, and leave the kiln run until a sample quits losing weight??   

[Don_Papenburg]

I would think that if you had a good support in the kiln roof that air springs from trucks  would be the ideal solution for weighting the stacks. 

[Dave Shepard]

beenthere, there is nothing scientific about our drying process. I try not to get involved, but every time I see something foolish going on over by the kiln, I get myself in the middle of it. The consistency and quality of the lumber coming out of the kiln is atrocious. The boss keeps asking me what to do to improve things, and then goes in some other completely opposite direction. I like th idea of using the airbags, we have tons of old trucks down in the junk yard. We could make a metal frame that drops down on either side of the fan units and just regulate the pressure for each stack.


Dave