Challenges of Drying Eucalyptus
Many ways have been tried to prevent Eucalyptus wood's tendency to warp and check, but none have proven to be highly successful. February 29, 2012
Question
We have many eucalyptus trees in California with incredible large clear boles. I think these are either Eucalyptus globulus or E. camaldulensis but I'm not sure. I've also seen many references to blue gum Eucalyptus so this may a common name for at least some of these large trees. While the wood is beautiful and plentiful there is a terrible problem with twisting and checking, so the commercial mills don't touch the stuff as far as I can tell. Is there any method of special handling, conservative drying, and conditioning that would result in reasonable yield for these beauties?
Forum Resposnes
(Sawing and Drying Forum)
From contributor G:
Vacuum kiln with an internal membrane that, being at ambient air pressure, provides 14.5 psi pressure on the stack to reduce warp?
From Professor Gene Wengert, forum technical advisor:
I have seen extremely slow drying to control checking, but then warp is high. I have seen every piece receive a metal band (1" wide) down the side about 5" then across the end and then up the other side 5" in an attempt to control end checks (due to growth stresses). Pre-steaming to relax the stresses has been tried. I have seen concrete weights on the tops of piles (10" thick slabs). All in all, I have yet to see what we would call successful drying on most pieces; expect some pieces (maybe a lot) to misbehave. (Note that there are many species of eucalyptus, so some species may indeed dry better than others.)
From the original questioner:
We will be drying with a Nile L500, so vacuum kiln is not possible. But Wood Doc, when you say misbehave, is this end checking (we could live with this)? Did the metal bands help? And why does slow drying cause warp? We would be drying 2 inch thick material.
From Professor Gene Wengert, forum technical advisor:
In brief: When we can dry lumber quickly, we develop an outer layer of dry wood that is nearly twice as strong as wet wood. This dry, strong region helps to prevent warp. If we dry slowly, we do not get this dry, outside region, so warp can occur more easily. This is also why when partially dried wood is rewetted, that warp (mainly cupping) will be excessive. The dry, strong outside region is no longer strong when it is rewetted.
From the original questioner:
So is this a foolhardy mission? Are the Eucalyptus globulus and E. camaldulensi species basically not possible to dry with reasonable yield? If there is loss but some reasonable yield it may still be worth it if the yielding boards are stable after drying. Is this the case provided of course that they are dried in the best manner possible? Are there any drying schedules available for these species?
From contributor O:
I believe the common name for those species is blue gum and red gum. I would totally forget 8/4 in a DH kiln. I believe the wood would sit there and refuse to dry. Eucalyptus is very hard to dry.
From contributor A:
You could try asking an Australian miller, as they are milling and drying all types of eucalyptus timber. It is native to Australia. There are millers at Heyfeild Victoria Australia. They should be able to answer your questions.
