Wood Drying/Moisture Content

[redbopeep]

Hey, guys, I've searched the posts and don't see an answer so here goes:

I've got some Douglas Fir coming down from Washington state (for my deck beams), the wood is 8/4 and 12/4 x various widths from 10" to 20", air dried. I know the moisture content ranges from 14-16% for the 8/4 and higher (up to 20%) for the 12/4.

We'll be doing deck beams in September (we hope!)

Questions--

What MC is OK to use without risking these beams warping/checking after we've put them in place. 20% seems a little high to go ahead and use, but...maybe not...?

Also, we'll stacking w/stickers outside but out of the sun (under an open tent) in a hot dry climate (So. Cal 80-90F until mid-Sept and um..low relative humidity 20%-65% day-night), any clue about how long might it take to get closer to the 16% or so MC? %/month? Any ideas?

Thanks!

[Bob Smalser]

I know the moisture content ranges from 14-16% for the 8/4 and higher (up to 20%) for the 12/4.



Assuming this boat will live in hot, dry California once you are done, you can expect DF in covered beams to have a moisture content as low as 6% (maybe as low as 4% even - ask Dave Fleming) at the end of your dry season and around 12% at the end of your wet season. The longevity of DF compared to White Oak isn't because it's more rot resistant...in fact it's less rot resistant...it's because it stays drier than oak during its working life, with significantly less time above the 20% EMC threshold required for mold spores to germinate.

As DF is only around 30% EMC in the log, 20% is still pretty green to build with. The problem won't be as much checking or shrinkage as it will be the moisture differential between the dry outside and wet inside of the stock. When it comes off the resaw looking like a banana peel, you'll know it needs more time in the stacks. Keep that fresh wood out of the San Diego sun however, or you'll prove me wrong about checking.

Shrinkage from 20% EMC to 6% EMC will be 2.3% across its vertical edge, 3.6% across its flatsawn edge, and 5.4% total shrinkage. That's a little over 3/32" in the flatsawn face of a 3" beam. DF if milled properly isn't prone to either warping or checking if kept protected, and I don't anticipate problems there. If there are problems, it'll be moisture differential spoiling your rips.

http://pic20.picturetrail.com/VOL12/1104763/3075040/214182916.jpg

But you still may be OK. DF is more forgiving about staying straight than many woods. When the stock arrives, borrow a moisture meter with a slide hammer electrode and 2" pins. Measure the EMC at different depths in the stock and see what you have. It's a much wetter Summer than usual up here where it was harvested and milled. If the green stock was kept well covered, you may not have any significant problems.

How long to bring 12/4 stock at 20% EMC to your September 6% equilibrium in sunny California by air drying? July or August of next year, I'm afraid. Jump in Californians if I'm wrong, but once the cool October rains come, I don't believe wood in San Diego begins drying significantly at all until the following April or May.

[redbopeep]

So, it sounds like I CAN use the wood but it will take a long while for it to dry out. Hum...now I'm beginning to wonder if we can work with this or not...we need to get the deck beams installed now, not in a year.

The boat will be going up to the Pacific NW once she's launched. She'll be here in So Cal though until sometime in 2008.

Other kiln dried DF on the boat was at 7% until we enclosed and humidified her a couple months ago, That wood now reads at 11% steady which gave me the impression that moisture levels change pretty quickly. Not so, eh?

The new wood will not be stored for drying in her humidified enclosure until its actually installed of course.

I don't have to take delivery of the wet wood, but cannot locate another reasonable source for the 12/4...

[Bob Smalser]

Other kiln dried DF on the boat was at 7% until we enclosed and humidified her a couple months ago, That wood now reads at 11% steady which gave me the impression that moisture levels change pretty quickly. Not so, eh?



From May to September they do. From October to April they do not.

I didn't say you had to wait. I said you have to check its moisture differential. Either with a good meter or some test rips. Whether the stock remains straight when ripped will tell you if you have to wait or not.

If the enclosure you are using raised 7% kilned wood to 11% in two months during a San Diego summer when the reverse is normal, then that's either a heckuva enclosure or somebody should consider checking their meter and technique. Pinless meters only measure moisture at the surface of the wood and are worthless for your purpose of determining moisture differential. A misted surface could read 11% with the wood beneath it still at 7%. How was the moisture content of the in-transit stock measured?

[redbopeep]

It is a very good enclosure with a greenhouse fogging system in place and its a Tramex Skipper pinless moisture meter. The meter measures either at surface or at depth between .25-.75 inches.

I will ask my Washington state contact to give me some info on the range of humidity levels he found present at various depths in the wood before he sends it down here. It is not yet in transit, they're preparing the shipment today/tomorrow. He just checked levels today but I wasn't bright enough to ask all the right questions...

My biggest worry is warping.