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Fudge factor for moisture meter?

Post in 'The Wood Shed' started by danham, Feb 7, 2013.

  1. danham

    danham Member

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    I'm dealing with some crappy wood I got suckered on, so bought a moisture meter to see just how bad things are and also to try to sort the wood into piles of "no-way this year," "maybe" and "this should burn."

    The meter instructions say to get the pins in 5 mm. That isn't going to happen on most splits I've tried. I'd have to hammer on the meter. So for rough sorting I began stabbing splits on the end best I could. I know this is less accurate than measuring a fresh split, but bear with me. I ended up with two piles: one of pieces that measured 20% or higher (max was 24%), and another pile of pieces less than that, ranging from 13-19%.

    I brought one of the "better" pieces indoors and measured the moisture at the ends again -- 17% -- then split it and measured fresh wood -- 21%.

    I haven't burned any of this wood yet, but a few questions. Is this meter inaccurate? A lot of this crap burned as if it were 30% wet (will never use this dealer again). Is a 4% difference between the end and the fresh split typical, and can that be used to estimate without splitting?

    It looks to me like this cheap meter ($20) may only be useful to do comparative, not absolute measurements.

    Your thoughts?

    Thanks,

    -dan

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  2. Backwoods Savage

    Backwoods Savage Minister of Fire

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    A reading on the end is about worthless for sure. I wonder if you took an awl and punched two holes then immediately put the meter in if it would give a somewhat accurate reading.

    Learn from this Dan. There is a reason we recommend getting 3 years ahead on the wood supply. Good luck.
    cptoneleg likes this.
  3. DanCorcoran

    DanCorcoran Minister of Fire

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    Measuring the ends means nothing. They are the first area to dry and can be dry as a bone while the inside is full of moisture. Others have suggested using a nail or other small object to make holes for the meter, to keep from bending the meter pins. The only meaningful measurement is taken from a freshly split face, with the pins parallel to the grain.
  4. cptoneleg

    cptoneleg Minister of Fire

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    Fudge all you want , but it doesn't make your wood burn any better.
    Backwoods Savage likes this.
  5. danham

    danham Member

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    OK, thanks for the comments. Yes I know about buying, stacking and aging. This wood still s*cks.

    At any rate, dealing with what I have in hand for now, does anyone have a helpful opinion on the meter reading I got with the fresh split? Shouldn't 21% burn adequately (it didn't; I have now tried it and it was wet and hissing)? Is this meter defective?

    -dan
  6. bogydave

    bogydave Minister of Fire

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    Fudge factor ?
    ± 15% give or take 5% or so :)
  7. gzecc

    gzecc Minister of Fire

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    Split a few pieces. measure them all in the center of the split. Do you know if all the wood is the same species? What you will notice with border line wood is that large pieces will show higher moisture content. Your hand should be in the low 30's, the molding in your house should be below 10%. Use the monitor as a reference. After a little time with using it you'll know your wood!
    danham likes this.
  8. jdp1152

    jdp1152 Minister of Fire

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    You can usually get a good gauge on a MM in the spring or fall when you have your windows open instead of using heat or AC. On a pleasant spring or fall day, your dry wall should be in the 7-10% range on the perimeter of the house. A bit higher for ceilings. Don't be alarmed if it's higher. Winter without a humidifier should read 0-7%. Summer with no AC, upwards of 20%. I'm surprised you can't get 5mm into a grain. I measure red oak from time to time and all I need in a good push. You've probably passed a 5mm kidney stone and never known it.
  9. HDRock

    HDRock Minister of Fire

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    Like said , end means nothing,never check there !!! Split it, check it, sort it.

    3 or 4 in diameter checked on face grain is pretty accurate
  10. Jon1270

    Jon1270 Minister of Fire

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    This is exactly right.

    A pin-type moisture meter measures electrical resistance. The MC reading it gives you depends on how the manufacturer calibrated it, but the standard calibration is for Douglas Fir at 70 degrees F. So what your meter is saying to you is, "I can't tell what kind of wood this is and I can't tell how warm or cold it is either, but assuming this wood you're sticking me into is a piece of doug fir at room temperature, then the MC is approximately X%." Species other than doug fir can throw it off by a percent or two. Cold wood will make it read artificially low. There are commercial-grade moisture meters that have built-in species and temperature correction, but they cost on the order of 10x what the typical cheap MM costs, and they still won't give you a meaningful reading without somehow getting the contacts deep into the wood.

    In almost any piece of wood there will be a gradient from wetter parts to drier parts. The reason it says 5mm is that the meter and the instructions written for it were designed for measuring the MC of sawn boards used for furniture, cabinetry, moldings, flooring. Most of that wood is rough-sawn at 1" thick (~25mm). 5mm is 20% of the thickness of the board, which is where you're reasonably likely to get a reading that's roughly equal to the average MC over the full thickness. A more accurate instruction sheet would tell you to push the pins in to a depth equal to 1/5 - 1/3 the thickness of the piece. With a 4" split of firewood, you'd have to stick the pins in *at least* 13/16" from the outside, which obviously isn't going to happen. So, we resplit. Since resplitting every piece just to measure the MC gets to be ridiculous, we look for ways to avoid doing it. We tap on the end of the split and listen to it. We look at the ends for discoloration and cracking. We lift pieces and judge whether they seem heavy or light for their size and species. And most of all we keep a couple years' worth of properly-stored wood on hand at all times, so we're always burning stuff that has seasoned for a long time and we don't have to think too hard about it.

    A moisture meter is good for checking a few representative sample spits from a pile that was all CSS at the same time, but it's not all that useful for sorting through a big pile mixed stuff to find the best (or least bad) pieces. For that, you're better off falling back on sight and feel. You'll get better with practice.
    Trooper, Gark and danham like this.
  11. Ralphie Boy

    Ralphie Boy Minister of Fire

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    I use a M.M. as a minor reference and curiosity tool only. I've found the best way to measure the moisture content of my firewood is with a multi-year calendar.;)
    danham likes this.
  12. danham

    danham Member

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    Great advice and info - thanks. One question, given that we are about to experience a blizzard, is it wise for me to be sticking the pins into my flesh to calibrate the meter? I mean hey, the e-room might be closed [grin]. And my wife might not be too happy with holes in the dry-wall.

    Kidding aside, the temperature issue is a big ah-hah. I was measuring outdoors at around 25F. And the advice about using eyes and ears for the big decisions is right on. I fresh-split a piece that I "liked" late last night that was at room temp and it read 21% and burned just fine.

    Thanks again, and you folks in the blizzard warning area, stay warm & safe.

    -dan
  13. gzecc

    gzecc Minister of Fire

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    Just be sure to wipe the pins with alcohol before the hand test and of course have some sterile dressings for wrapping the wound. Make sure to test the most prominent piece of woodwork and or drywall you have in your home. These will be the best test samples!
    StihlHead and danham like this.
  14. HDRock

    HDRock Minister of Fire

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    With today's technology inexpensive moisture meters , are a far better indication, than smackin some wood together, but if dried 2-3 years probably not necessary.
    Many , do not possess 2-3 year seasoned wood
    Lumber-Jack likes this.
  15. clemsonfor

    clemsonfor Minister of Fire

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    Yea even that 24% should burn fine. Split say 3 pieces into really small ones to get a fire going really hot with many coals then load that wood on top of the coal bed and run the air wide open for 15 mins then back it down it will burn like wildfire!
  16. jdp1152

    jdp1152 Minister of Fire

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    How big are your pins and how far are you planning on stabbing the wall? I stick em in the drywall all the time to monitor a few old leaks and the holes aren't even noticeable.

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