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Author Topic: Kiln drying hemlock  (Read 419 times)

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Offline PAmizerman

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Kiln drying hemlock
« on: April 27, 2018, 05:51:50 PM »
Well I got a call today. A local construction company is working on building an environmental center and needs 30,000 feet of hemlock. I'll rewrite that so you don't ask me if I screwed up
:D. Yes 30,000 board feet.
Problem is they want it now and want it no more than 15% moisture content.
So my question is can hemlock be kiln dried effectively? And how long would it take? I just wish peaple could plan ahead.
What is the minimum amount of time to air-dry hemlock?
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Online moodnacreek

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Re: Kiln drying hemlock
« Reply #1 on: April 27, 2018, 06:11:11 PM »
No body plans ahead except maybe farmers. I have gotten w. pine and spruce below 15 per cent in 4 weeks in march cross ways in the wind, roofed over.  That was 1 x.

Offline GeneWengert-WoodDoc

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Re: Kiln drying hemlock
« Reply #2 on: April 27, 2018, 10:48:03 PM »
I assume that they want Eastern hemlock and not Western hemlock.

There is an issue: Many hemlock butt logs that are over 75 years old have a bacterial infection that increases the green MC, that causes wet pockets at the end of drying, that causes shake or wind shake, and that weakens the wood.  So, if you will be doing the logging or sawing, you will not get the best yields with older logs.  Most large mills know this, so Eastern hemlock is not very common in the lumber market.  Drying is hard because of the wet pockets...a lot of the lumber will be dry in 21days...depending on thickness, grain, kiln equipment, kiln schedule.  However you can add a couple of weeks or more for the wet pockets.  They have perhaps 30% more moisture to start with and dry slower than "normal" wood.  If the piece averages under 15% MC, will they accept it even though a few small areas are 25% MC or so?

If they want under 15% MC, this is a traditional MC level.  But how dry will they accept.  Much under 11% MC and the wood gets brittle when machining. Will they accept some end splits and chipped grain from the planer, or will you have to eliminate those pieces? The smaller their tolerance, the longer it takes.  The same with is a tree defect that shows up after drying and is usually a defect that drops grade to the lowest level.  Will you have to suffer the loss for this defect?

Air drying time to under 30% MC depends on the weather, but two months minimum, not considering wet pockets.  Because the relative humidity in your area is around 65% RH, it will be hard to achieve under 20% MC in three months.  The EMC is around 13% in your area, so after a year you can get down to 15% MC.  Really hard to get from 15 to 13% MC if the outside is 13% EMC.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

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