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Weight loss in air drying

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Eric Johnson, Jun 2, 2006.

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  1. Eric Johnson

    Eric Johnson Mod Emeritus

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    According to my reference ("Log Rules & Other Useful Information" published by the Northeastern Loggers' Assoc.), the following species lose the indicated amount of weight when going from a green state to "air dried," which is defined as 20 percent moisture content. This is derived from estimates of the weight of sawn lumber.

    I got to thinking about this the other day during a discussion in another thread about how to figure out how dry your wood is. I think weight is the best indicator. If you take a green sample piece and weigh it and write down the result, you should be able to get a good idea of how much it's dried at any time by weighing it again and making a comparison.

    In this case, moisture content is the amount of water (by weight) relative to the amount of bone-dry wood. That's how wood moisture content is usually calculated, occasionally resulting in mc readings in excess of 100 percent for some species when green.

    Anyway:

    Beech - 24%
    Hickory - 27%
    Black Cherry - 28%
    Soft Maple - 29%
    Hard Maple - 30%
    Yellow Birch - 30%
    Red Oak - 31%

    Given the margin of error, I think it's safe to say that they're all in the 30% ballpark. Let me know if there's a species not listed that you would like a number for.

    When sawmills check mositure content of lumber in their kilns, they use a fancy (expensive) moisture meter which can be driven deep into the piece of wood. They also take their samples from the middle of a stack in the middle of the kiln. You should do your weight sampling from a piece in the middle of your pile, if possible. Firewood from the top and/or edges of the pile or stack dries faster and thus will not give you a representative sample.

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  2. elkimmeg

    elkimmeg Guest

    Another spin a green wet red oak log weighs 15 dry 20% moisture content should weigths 10 lbs or less
  3. Eric Johnson

    Eric Johnson Mod Emeritus

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    That's an interesting approach, elk, but it works.

    15/2 = 7.5 x 1.2 = 9 lb

    EDIT: I thought I had that figured out, but now I'm not so sure. Can you elaborate on your method? Math ain't my strong suit.

    EDIT:/EDIT: Thanks Harley! Duh! (pulls knuckles from floor and smacks open palm against protruding forehead).
  4. Harley

    Harley Minister of Fire

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    perhaps oversimplied, but if you use the "ballpark" 30 %, then in Elk's example, 15# log

    15 X .7 = 10.5# after drying
  5. wg_bent

    wg_bent Minister of Fire

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    Did they list Pine, Sumac, Poplar or Mulberry?

    Pine is incredably light even when pretty green. I've got some rounds in the yard that are about 19" across and they're no problem to pick up, whereas I had some similar sized Cherry a few weeks ago and that stuff is almost impossible to pick up a 19" round that's 15" long.

    On the Other hand Poplar is really heavy when wet, yet I suspect it will loose almost 50% of it's weight when dry.
    Mulberry is similar to Poplar. Very heavy green, but very light when dry.
  6. Eric Johnson

    Eric Johnson Mod Emeritus

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    No luck on sumac or mulberry 'cause they're not commercial lumber species.

    As to pine, I have 10 different flavors listed. In the case of eastern white pine, the number is 28%. Ditto for loblolly. Shortleaf is 38%.

    When you say poplar, if you're talking about yellow (tulip) poplar, it's about 18%. If you mean Lake States popple (aspen), then the number is 41%. Interesting.

    While we're at it, I forgot to include another popular firewood, ash, in the original list. White ash checks in at 14%. That's why they say you can burn white ash even when it's green.

    Obviously, if you were trying to decide which species to burn green, the lower the number the better.

    Not that I'm recommending that with ash or any other wood.
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    Another wrinkle to this process is that the rate of transpiration varies from species to species, presumably due to the each wood's unique cell structure. Yellow birch, for example, gives it up slowly. IME, you need to air-dry yellow birch for two years under normal conditions to get it to dry sufficiently. Cherry and soft maple, on the other hand, seem to get rid of their water pretty quickly. White oak takes longer than red oak. And so on.
  8. Sandor

    Sandor Minister of Fire

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    I read about the weighing method years ago, but they did not supply numbers. Thanks Eric.

    Nowadays, I find myself picking up the piece, and just giving it a feel. I can pretty much figure if its "dry" or not. Not scientific, but after 20 years, it works.

    Think I'll play around with the bathroom scale this year on some green freshcuts. Watch the weight, and try to extrapolate the drynessness from the appearance (color, radial cracks) on the rest of the pile.

    Sitting back with beer with the serious look..... "Yea, thats 20%"
  9. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    God I miss the days before hearth.com. All those years when I just cut it, split it, stacked it and forgot about it until winter. Now my freakin chimney is lined, the wood is put up earlier than any time in history and all I can think about is "Gosh, I wonder how well it is drying? Should I cover it? Should I take the cover off on the sunny days? Better get the moisture meter and check it! What if it rains tonight?"

    Arrrrrrguh!
  10. elkimmeg

    elkimmeg Guest

    Hey how you doing recovered yet?
  11. wg_bent

    wg_bent Minister of Fire

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    Or we could just burn coal in stoves and really forget about all this....eco alert... eco alert!! :)
  12. Sandor

    Sandor Minister of Fire

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    If your asking about my Lymes disease..... about 75%.

    My eye stopped twitching last week, joint pain gone, but stamina is hurting. One more week of the antibiotics to go.

    Thanks for asking Elk, like one big family!
  13. PAJerry

    PAJerry Member

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    Interesting fact about ash. I guess if I run out of wood next spring and can go out and cut one up to stay warm - got lots of it out there. Doing some checking on the emerald ash borer. Hope it never gets here but I got a feeling it won't be long.

    I used to cut wood for the fireplace in September to burn that winter. Now that we have the stove- and hearth.com - it was all done before May 1 and I have a few pieces I check by picking them up to check how dry it's getting. Seems to be progressing well with plastic just on the top to keep the rain out.
  14. wg_bent

    wg_bent Minister of Fire

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    Same here Jerry. I started putting chicken wire on top of the wood, then the plastic. It keeps some air space above the wood, and keeps the plastic from conforming to the wood. then water doesn't collect on top of the plastic at all. It works MUCH better than plastic alone.
  15. Eric Johnson

    Eric Johnson Mod Emeritus

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    That's interesting, Warren. I'm trying to figure out a good way to keep my pile tarped over the winter, but without getting big pools of water (chunks of ice) forming in the voids between the piles. The bigger the pile, the harder it gets.
  16. wg_bent

    wg_bent Minister of Fire

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    I guess I should be a little more specific as to the fencing I use. It's the green wire fencing with spaces that are 1x2" rectangles.

    It's left over from a lot of fencing I removed when I moved into the house. It's quite stiff and works really well. I use 6mil plastic too. It's a lot tougher than 3 mil.
  17. fbelec

    fbelec Minister of Fire

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    we had this discusion last year sometime and someone i can't remember who, said that if the wood gets to dry it would burn up fairly quick and not throw alot of heat. if that's the case, when this ash starts drying it won't be to good. at 14% it's almost good to go as is to keep it from burning up quick. i know this sounds dumb. i have some ash waiting to be stacked right now. it was a tree 2 months ago but now it very light in weight. it almost feels dry. and if you hit two pieces together it makes the dry wood klunk sound.
  18. Eric Johnson

    Eric Johnson Mod Emeritus

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    Warren,

    I know the kind of fencing you're talking about. That would work great, I think. I have some that's orange; it would make a great base for a tarp. Lattice would work just as well too, I think. A slight slope or crown should be all you need to shed water.

    fbelec,

    Those percentage numbers are a little confusing; I had to look back to refresh my memory. The 14 percent is the amount of moisture (by weight, compared to the solid wood) that needs to evaporate to get the ash down to air dried state, or 20% moisture content. Once it gets there, it shouldn't get any lower, at least not for awhile under normal conditions. It just gets to an air-dried state more quickly than most other woods, because it contains less water to begin with. In my experience, 2-year-old ash is excellent firewood.

    Getting too-dry wood is kind of like getting too rich--it probably won't happen to most of us.
  19. PAJerry

    PAJerry Member

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    I'm using the 6 mil plastic too. The wire idea sounds great, though I only have some regular hex-mesh chicken wire available here right now. I going to try it on my pine stack and see how it works. Thanks Warren.
  20. Eric Johnson

    Eric Johnson Mod Emeritus

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    Somebody else said it first in another thread, but the best firewood cover I've ever used is used lumber wrap from the lumber yard. The only trouble is that you're living with a lumber company logo.
  21. fbelec

    fbelec Minister of Fire

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    ok got it now.
    can you turn those wrappers inside out?
    i use black 6 mil plastic. i'm on my second year .
    not to expensive 50 foot roll
  22. Eric Johnson

    Eric Johnson Mod Emeritus

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    Come to think of it, fbelec, I think you can.
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