Drying Green Timber

Hello!

I’ve just had a tonne of jarrah and marri milled into planks of various sizes (180mm x 40mm to 50mm x 25mm), all around 2 metres long.

Just wondering if anyone can offer tips on drying the wood to make outdoor tables and benches? I have a 7 month deadline so cannot do the standard “1 year per inch thickness”.

I have built a drying box in my backyard, consisting of an enclosed and insulated box (2m long x 1m x 1m) with a 150W heat lamp, small battery-powered fan and ventilation.

So far i have noticed the marri is cracking faster than the jarrah, and that the thick timbers (75mm x 50mm) are experiencing the most cracking. I have sealed all ends with mineral turps so far, and plan to add another coat of PVA glue and water mix when I have time.

I'm still relatively new to woodworking so any suggestions are appreciated.

Cheers,
Tom from WA's southwest

turn the lamp off, open the box up, wet it well a couple times a day for a week, and let it air dry to below 20% MC before going any further. It's probably too late but you might save some of it. You might get lucky but chances are you're making really expensive firewood right now.

A couple of years air drying :oo: and then when you dress it it will still want to crack and twist:o.

Without a properly regulated kiln I'd say you are battling to dry them without significant damage in 7 months.

Mineral turps doesn't do any significant sealing so that will be part of your problem.

Where is the box? is it is the sun or under cover.
It's really easy to cook the wood in such a small container with a box in the sun.
How many CFM of ventilation, and CFM of recirculation (this is essential - you need more of this than ventilation) have you got.
Does you heat lamp shine directly on any timber?
If you have no recirculation the humidity and temperature differentials inside the box will make a real mess of the timber.

It is important to air dry green timber before kiln drying and then good practice to air dry again after the kiln. Your time frame is of no interest to the timber and acceleration will only create problems. This material is not for your current project.

Thanks mate will do. I've got a moisture meter so will keep track of it. Once it's all below 20% MC can I turn the lamp on again to dry effectively? Maybe like every second day?
Also, the logs had been sitting out for about a year before being milled so they're not super fresh. Thanks for your input.

Ok thanks mate that's good advice. The box is undercover. Not sure of the CFM but it's definitely recirculating over ventilating as the fan is positioned far from the small vents.

Yes the heat lamp shined directly on some of the timber, but I've resolved to switch it off until the wood is below 20% MC. Shall i position the lamp so the light is completely deflected? Thanks for the input.

Thanks mate, to note is that 95% of the timber is air drying, only 5% is in the drying box (which I've switched off thanks to suggestions here). Any rules of thumb for the time frames between air drying -> kiln drying -> more air drying? Cheers.

I built the Virginia tech solar kiln https://www.pubs.ext.vt.edu/content/...20-030_pdf.pdf in Canberra. I added a 36V solar panel and wired a 12v attic fan through a 36V to 12V step down box. I am currently deciding whether to add a 2nd fan... Its not a pretty kiln but it works fine in Canberra winter with a 45 degree roof.

The idea of the solar kiln is that it cools off every night releasing the stresses caused by drying

For its first run I put 2" thick cedrus antlantica in our drying shed racks for 2 to 6 months (from 2 different logs) as the moisture just falls out in the beginning. I then put both stacks in the Kiln for 6 weeks with all the vents closed to retain humidity, followed by 2 weeks with the vents open. It turned out great. Basically I take out a board every week, weigh it, and when it stops getting lighter, its dry enough.

I currently have a mixed load of 2" thick pseudoacacia robinia, cedrus atlantica and Ulmus Procera in there, due out on the October long weekend.
I intend to follow the same process. When the boards stop losing moisture with the vents closed, I'll open the vents, when they stop losing moisture with the vents open or it slows down to a dribble, I'll unload the stack and process a board to do a weight check against dry weight (which I can establish for any species by microwaving a test piece till its dry, although I also double check the reference library)

The ends of all boards are sealed with end grain sealer, up to 1" from the end.
All boards are stickered with 19mm square stickers. Sticker placement is at the ends, and spacing on 400mm centers.

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Originally Posted by tom_southwest

Thanks mate, to note is that 95% of the timber is air drying, only 5% is in the drying box (which I've switched off thanks to suggestions here). Any rules of thumb for the time frames between air drying -> kiln drying -> more air drying? Cheers.

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3 months air each side of the kiln up to 50mm. Over 50mm requires more like 6months prior then 3 months after. This is rule of thumb only and seasonal changes will need to be factored in. Always better to err on the side of longer air dry where possible.