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Thread: Blue dot mold on green turnings

  1. #1
    Join Date
    May 2009
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    Blue dot mold on green turnings

    I had a large Birch trunk laying outside all winter and just now got it sectioned and turned into 4 large,13"+ diameter bowls of various shapes. Immediately upon completion they were coated with Titebond II and set aside to dry. Picked them up the next day for weighing and noticed significant blue/gray mold spots under the PVA sealcoat, and growing daily. Having never encountered this before I'm wondering what to do, if anything. I'm particularly intrigued by the fact this is growing under the sealant. Any help will be appreciated.

  2. #2
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    Nov 2009
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    You will have to get the glue off to treat the mold with some household bleach.

  3. #3
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    Quote Originally Posted by Richard Coers View Post
    You will have to get the glue off to treat the mold with some household bleach.
    I am curious as to what happens if I do nothing. Will the wood rot? Or will the staining continue rendering the bowl esthetically unacceptable?

  4. #4
    I know maple loves to mold like that under plastic wrap, which I do to all of my bowls other than maple. You can bleach it out, which I don't like to do unless pretty much the whole thing is dipped in bleach. I don't really know if you can get it out after the bowl reaches equilibrium. You may be able to turn it out, cut again, I don't really know. I think it is possible to bleach it out before you seal it. Pretty sure others will chime in here.

    robo hippy

  5. #5
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    Aesthetically unacceptable? That’s a matter of opinion - but what needs to be said is that the wood was molding before you sealed it. Will it continue to mold? Yep. If it’s not too late, put it back on the lathe, take an eighth or 3/16 from inside and out. Spray with a solution of boric acid, let it dry and then seal. Clorox will work, too, but the chlorine bleach tends to evaporate leaving behind the water component - the one thing mold loves, so ultimately, it comes back. Boric acid is readily available, kills mold and bugs really hate it. Better for long term storage on the drying shelves. I’m not a chemist or a doctor, but I understand that it’s no more dangerous than bleach as long as you don’t eat the powder…I spray my storage area every now and again.

  6. #6
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    The out sides were done and sealed on Thursday. Placed under a wet towel for the night. Friday I turned the insides and immediately sealed them. By Saturday morning the mold had started.And itís worse today. Apparently semi anaerobic bacteria since they are growing under a good coat of Titebond. (Possibly the source of the bacteria is my old brush which I store in a moist environment) Iím asking if anybody has experience with leaving the bowls alone. Will the the mold permeate the wood, staining it or worse? Iím quite willing to turn it off but am wondering if I really need to.

  7. #7
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    Aug 2013
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    Providence, RI
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    Quote Originally Posted by Bernie Kopfer View Post
    Will the the mold permeate the wood, staining it or worse? Iím quite willing to turn it off but am wondering if I really need to.
    That really depends on the organism you are dealing with. Get back to us after you have the lab results.

    You could leave it alone and see if the results turn out to be aesthetically pleasing. If you don't want to take that chance, turn it off now.
    -- Jim

    Use the right tool for the job.

  8. #8
    Join Date
    Mar 2003
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    Ontario, Canada
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    The PVA is not bothering the mold, i.e., it isn't inhibiting it. I think you've just created an ideal condition for mold growth - lots of moisture and your attempts to prevent cracking have reinforced it. You need to get the moisture content down to inhibit mold growth.
    I don't coat my bowls all over, I only seal, using Anchorseal but whatever you want, the outer end-grain. The side-grain component doesn't lose moisture very fast. Sealing only the outer end-grain slows the loss but doesn't prevent it. I also wrap fresh turned wood in newspaper and put in a box or paper garden bag. In the first few days the paper usually gets soaken wet and needs to be changed to get rid of the moisture.
    I've had good luck with this method but nobody can ever guarantee 100% crack-free and how prone a piece is to cracking is also species dependent along with the conditions the tree grew in - trees in windy locations, for example, can have more internal stresses than their sheltered friends.
    Last edited by Bill Howatt; 05-16-2023 at 9:27 AM.

  9. #9
    A drying bowl cracks because parts of it dry out too fast relative to other parts, causing the a nonuniform reduction of size. This creates pressure to crack.

    So, the goal of drying a bowl is to get the moisture to leave more uniformly.

    Moisture wants to leave the end grain and sharp edges quickest. So those areas need to be coated.

    The best coating IMHO is a substance that only slows down the moisture release - not stops it. Your PVA IMHO is trapping too much moisture. The bowl WILL eventually dry even through the PVA, but risks leaving mold in its wake.

    Wax is a better choice. Coat at least the end grain and the rim.

    Moisture loss in a bowl happens very rapidly at the beginning and then tapers. Sometimes I get a log that is so fresh and green, it spits water as a rough it out. When this happens, I leave the bowl uncoated for a few days. That initial rush of free water will leave quickly, and won't cause cracking quickly except near the pith (so get the pith out - always, if you can). After the bowl is no longer "wet" but only very mildly "damp" or less, then I coat.

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