Air drying eucalyptus

[AlexA]

I have some 10/4 think, 10 inch wide, and 22 inch long boards of Tasmanian Blue Gum (eucalyptus globulus) which I am planning on air drying to become chair seats. This stuff is soaking wet right now (only milled a week ago) and i know this wood can be temperamental.

After some research I found several research papers on the subject will a focus on commercial drying. This one mentions block stacking the boards and keeping them wrapped in plastic for 4 weeks before racking and drying in a solar kiln. http://www.fwpa.com.au/images/processing/PN03.1315.pdf

Has anyone tried this? I have stacked my boards in a tight cube and wrapped it in plastic. I'm planning on letting them sit for a few weeks but this seems like the block stacking would cause drying speed discrepancies.

has anyone tried this?

[Guest]

Alex,

I have virtually zero experience with, and certainly expertise in, drying wood, especially eucalyptus which doesn't grow here. However, I read the paper published by the Australian wood products people you linked. It sounds to me like the plastic wrap was done to facilitate the absorption of the boron diffusion solution they applied rather than as part of the drying process, which was done after the boron treatment. If you are not treating your timber with boron, it sounds like the plastic wrap would be counterproductive to your goal of drying the timber.

For what it's worth, I purchased some 8/4 ebony online for saw handles. It was represented to have been air dried for many (don't remember how many) years. Nevertheless, it arrived with 18% moisture content. I needed it to be less than 10%. Ron Brese uses a "finishing kiln" to dry relatively small pieces of exotic timbers for his wonderful hand planes. It's nothing more than a chimney made of light 1/4" plywood on a simple frame with an incandescent light bulb at the bottom and a rack on which the wood is placed. The heat from the light bulb rises up the chimney and creates a very gentle draft that passes by the timber and accelerates the drying. You can vary the tempreature and the volume of air rising through the chimney by increasing or decreasing the wattage of the incandescent bulb. I built one of the kilns and successfully dried my ebony handle blanks. I started with a 60 watt bulb and changed it to a 100 watt bulb after about two months. In three months, I was able to dry my 8/4 blanks from 18% MC down to 7% with no checking splitting, case hardening or any of the other calamities that can occur from improper drying technique. A simple finishing kiln is probably impractical for large boards, but for smaller pieces, it's just about perfect. Here's a picture of mine:



Good luck with your eucalyptus.

Hank

[AlexA]

Thanks Hank. That is a pretty simple solution for trying small pieces that could be broken down when not in use.

I was wondering the same thing about the boron but I have seen plastic wrap mentioned in other papers as well as a form of pre-treatment, I think it is to slow down drying to minimize collapse.

The thing that concerns me is that none of them mention the block stacking. I could see the block staking being done to minimize warping, but it seems like that would increase the moisture gradient.

From your read, was the block stacking only for shipping/boron treatment or do you think it was kept that way for those 4 weeks?

[AlexA]

I just re-read the paper and realized they had painted the end grain prior to milling. That would help to reduce the end grain drying. I better do that when I get home tonight.

[Guest]

Alex, you must keep in mind that I know absolutely nothing about this subject except what I read in the Australian Wood Products paper. It sounds to me, though, that the initial plastic wrap and block stacking took place immediately after sawing. I don't know how fast Lyctid infestation occurs, but it would be my guess that the initial wrap and block stack was done to minimize the exposure of the freshly cut wood to the beatles and protect it intil it could be transported to the treatment facility and treated with boron. My reading of the article doesn't indicate how the lumber was stacked after it was treated, only that it was wrapped in plastic for four weeks, after which it was "racked out" for drying. The wrapping and block stacking may, indeed be part of the process to stabalize the wood prior to kiln drying, but I don't know that and I can't tell from the article. My very limited exposure to this kind of thing tells me that plastic wrap and block stacking would be counterproductive if your goal is dry the wood. I could be wrong (often am) and one or both of those steps may be recommended or required for your kind of eucalyptus. I probably shouldn't have responded to your post since I know zero about this topic. Sorry for talking out of my hat.

Hank

[AlexA]

the drying rig alone was worth the response :-)

Thanks for your thoughts.

[AlexA]

After some more research you were correct, the block staking while wrapped in plastic is to allow the boron to diffuse. I also should have painted the ends immediately after cross cutting.

I'll be racking the boards and painting the ends tonight when I get home and then putting plastic sheeting over the rack (for the first few weeks).

[Rick F]

Wow, I actually air dried some Eucalyptus. And some Pacific Yew.

I stacked it in the crawl space, kept pressure on it, and left it for 2 years.

Mine is cut 8/4. I painted the ends, some cracking, but honestly it dried really well..

[AlexA]

Thanks, I've sitckered them, painted the ends, and wrapped ratchet straps around the stack.

[AlexA]

On the off chance anyone else is looking to do this I wanted to add a update.

After a week stacked under plastic I removed the plastic to allow more airflow. We then had a few days of 70 degree temps with high winds which ended up drying out the boards way to quickly. some boards dropped from 30+% moisture do around 20% moisture and several boards checked very badly. They are back under plastic for the time being.

Boards are stored outside in the shade in a sheltered area of the yard.