Detecting moisture in end grain balsa

Discussion in 'Projects & Proposals' started by Barry_S, Feb 27, 2024.

  1. Barry_S
    Joined: Feb 2024
    Posts: 4
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    Location: Sydney

    Barry_S New Member

    I have bought a second hand Merlin moisture meter.

    When I use it on the boat, I see measurements from 4 to 39.

    4 being the driest and 39 being the wettest. When I find a high reading area I test it a few times to make sure and mark the boundaries. Then with a hole saw I cut a disc out of the top layer only to find the balsa is bone dry and looks like it has never been damp, ever. When I run the meter over that section again it reads low now. I experimented 3 times testing differently each time.

    Same result.....

    I'm new to these meters so maybe I'm doing something wrong but I have experimented with the settings and on other timbers, surfaces etc. The only thing that makes some sense is if there is humid air inside the layers and I release them when I take the top skin off, doesn't make a lot of sense granted but the best I've come up with so far.

    It is hot and humid.

    Any help appreciated
     
  2. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    End grain balsa readings are notoriously inaccurate because all end grain readings are notoriously inaccurate. Why? Well, the structure of wood is for it to dry outside in and the moisture levels are best read on the face of the wood, which is basically impossible. So, to get an accurate reading; you'll need to average maybe 4-6 end grain readings. The other thing is the meters are really meant to read the other way or across the grains.

    Another problem is pin length. If you use short pins or only have short pins, the reading will vary greatly in a day. And eventually, the pinholes will cause reading errors when on a coupon.

    Something I'd try is after removing the glass and getting a reading, tape a piece of plastic over the coupon surface and seal the edges all the way around. If that plastic gets water droplets on it; you don't need a meter to know your emc is over 15%, more likely over 20%. If the boat is outside, it is a best practice anyhow to avoid heading up to emc for a tropical zone.

    Another thing I have experienced is daily changes. The wood surface does dry faster than the whole board and this is highly worse in a coupon test. So, let's say you find 34% emc day 1. Day 2 you test and are please to find 29%. Day 3 you test it again and find 33% and wonder, wth. What is happening is the coupon area dried quickly, but then becomes a sponge for the rest of the wet wood. I've experienced this issue using halogen to dry a transom. After the light was shut off for safety reasons (never leave a halogen for drying unattended), I was always pleased the transom was getting so dry. The next day; it would be wet to the touch again. This issue went away after several drying days, but in a place where you are not using halogen; this phenomena will repeat for a long time.

    I'm actually not surprised in the variation you are seeing.
     
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  3. Barry_S
    Joined: Feb 2024
    Posts: 4
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    Location: Sydney

    Barry_S New Member

    Thanks for your response, the meter is the nondestructive (no pins) type, I assume the same applies.

    I'm interested in the halogen drying. How would I do this, can I buy a halogen drying light ?
     
  4. Tops
    Joined: Aug 2021
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    Location: Minnesota

    Tops Senior Member

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  5. Barry_S
    Joined: Feb 2024
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    Location: Sydney

    Barry_S New Member

    Thanks again Fallguy, I don't think it's for me though
     
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  6. Barry_S
    Joined: Feb 2024
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    Location: Sydney

    Barry_S New Member

  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Another way to remove moisture is with vacuum.
     
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  8. Howlandwoodworks
    Joined: Sep 2018
    Posts: 225
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    Location: USA MO

    Howlandwoodworks Member

    A inexpensive moisture meter will not give a accurate reading on a boat deck moisture level but it will show you where it is highest, maybe.
    Stud finding wall scanner works the same way by measuring the resistance of electrical flow through the said substances surface.
     
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