Re-Drying Southern Yellow Pine
Lessons learned from drying untreated Southern Yellow Pine. July 7, 2011
Question
I buy 5/4 SYP deck boards (before being treated) from a local pine mill. It has been dried in their pine kilns, but the MC is between 15 and 28%. So I sticker it and redry it to 9% in my kiln.
I redry it because I mould it into T&G, V-groove ceiling and wall paneling for indoor use. The problem is: I get a lot (25% or more) of warped lumber, mostly side bend, some quite warped and unusable. How can I redry this with minimal warp? I have a steam kiln, so I could add steam to the schedule if I knew what it was.
Forum Responses
(Sawing and Drying Forum)
From contributor D:
Sounds like you are getting quite a bit of juvenile wood, the tree's pith, near the edge of the lumber. When I dry quarter-sawn wood with the pith involved, besides cracking, I get a C shaped board, as you say, side-way bend. Try cutting the pith out before drying, 1-2" away from the pith, or order your lumber without the center of the tree.
From the original questioner:
Thanks for the reply, but I'm not cutting the wood - I buy it already milled, 5/4 by 6" wide deck boards. So, what I've got is what I got.
From Professor Gene Wengert, forum technical advisor:
SYP is known to be prone to warp, especially wood from trees that are under 25 years old. There is more warp the drier the wood is. Side bend is common, especially when the annual growth rings are not centered on the end of the piece. All in all, this warp is why we do not see much SYP in low MC uses such as furniture.
You can learn more about warp causes and cures at the link below.
Warp in Drying
From the original questioner:
Dr Gene, question. Remember the SYP has been dried once, per the SYP schedule I'm sure, down to 15 to 28%. When I dry it, I just dry it down to 9%, equalize for a few hours and quit. Would any conditioning help? And if so, what schedule?
From Professor Gene Wengert, forum technical advisor:
There is no schedule or process you cause that will help. Of course, make sure you never create conditions that will add moisture back to the surface.
From contributor D:
You may or may not find this interesting, but a company wanted me to dry 5/4 SYP down to 0% in one of my vacuum kilns. Why? They wouldn't say. I did and the wood came out straight as an arrow. Why? I don't know.
From Professor Gene Wengert, forum technical advisor:
Amazing indeed. I wonder if it was your kiln or the wood. Did you notice if the lumber was from large trees? Did you have to run the kilns in any special manner to achieve 0% MC?
From contributor A:
I saw and dry a lot of SYP and 9% is pretty dry. Do you get a lot of chipping and tear out? Most of mine I do in the 12 to 16% MC range and it machines well and does not move when installed.
I make 6/4 x 6 flooring and lose maybe one out of a hundred boards. Most of it has to do with the trees and sawing with the pith centered on the board. Most of my pine has 10 rings or more per inch.
What you are buying is boards that never get dry till they are installed on a deck. Then they can not move. If you buy deck boards and leave them out for a few days, they will bow all over the place.
From contributor D:
Gene, they cut the ends off and took them with them. The rest is still laying here so I got another look. They sure weren't big trees and there was no special cutting. As far as kiln settings go, I used a higher than normal temperature and a lower than normal pressure.
Click here for higher quality, full size image
From Professor Gene Wengert, forum technical advisor:
Awesome indeed.
