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Experiment: Tracking drying by weight

Post in 'The Wood Shed' started by Jon1270, Feb 24, 2013.

  1. Jon1270

    Jon1270 Minister of Fire

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    I took down a young mulberry yesterday, and am now trying an idea that I've been toying around with for a while. When I got home I lopped about an inch from the end of a split, and weighed both pieces with a kitchen scale.

    MulberryInitial.jpg

    I dried the small piece completely in the microwave (also left it in a warm conventional oven overnight to make sure) and weighed it again.

    MulberryTest2.jpg

    The difference between the original weight and the oven-dry weight tells me how much moisture there was to begin with, which in turn lets me know what the initial MC was for both the offcut sample and the larger split. The sample started out at 214 grams, and at oven-dry was down to 114 grams. It lost 100 grams of water (the nice round number being pure coincidence). 100/114 = 0.87.7 = 87.7% initial moisture content.

    The big piece started out at 3074 grams. I can now measure the average moisture content in that split very accurately by weighing it and doing a little math. It will hit 20% MC when it gets down to 1,965 grams.

    I intend to weigh the split every Saturday, and periodically post updates here.
    fox9988, albert1029 and ScotO like this.

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  2. red oak

    red oak Minister of Fire

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    I think you have to use the original starting weight - 214. So it would be 100 / 214 which gives me 46.7% moisture in the original assuming that at 114 it is bone dry. It'd be interesting to see if it gains weight if it's sitting outside.
  3. Jon1270

    Jon1270 Minister of Fire

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    Actually, both are correct. I'm using the "dry basis" measurement, i.e. the dry weight is the denominator. You're referring to the "wet basis" method. Electronic moisture meters estimate dry-basis moisture contents. The difference in the numbers is magnified when the wood is very wet, but it matters much less when you get down to burnable levels. 20% dry-basis is roughly equal to 17% wet-basis.

    It won't do that unless it sits in a puddle. The split dropped about 1% just overnight.
  4. ScotO

    ScotO Guest

    I LOVE a good back yard experiment......You do realize, however, that this test will be much different with each species of wood, right?

    Try this experiment with, say, white oak, and you'll get different results over a longer period of time.....

    I'm waiting on someone to invent a microwave that I can fit 8 cord into at one time, that will run on solar power, that I can dry out my splits in a matter of a day or so.......that would be an invention that would revolutionize the wood burning industry!! I plan on building a solar kiln/hybrid woodshed someday, but I have too many irons in the fire right now......
  5. Jon1270

    Jon1270 Minister of Fire

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    Yep, I'll do that when I have a chance. A limitation of this approach is that you have to cut and weigh the pieces very soon after the log is bucked. If the end is allowed to dry out before you slice off the sample for oven-drying then the MC of the small sample won't be representative of the larger piece. A neighbor plans to take down a white oak sometime this spring, so I'll have the chance to grab a fresh sample and whisk it off to the lab...
    ScotO likes this.
  6. Jon1270

    Jon1270 Minister of Fire

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    I just realized that you were probably talking about the oven-dried sample, not the big split. I expect that would gain weight sitting outside. I'll toss it out there and see...
  7. Jon1270

    Jon1270 Minister of Fire

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    A four-week update, in case anyone is interested. MC of my test Mulberry split is down to 71%.

    MBT1.jpg

    That little oven-dried slice, which I put out with the split, rebounded quickly. It's currently at around 16%, where I imagine it will more or less stay.

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