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Thread: Problem varnishing in corners

  1. #1
    Join Date
    Sep 2016
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    Central Missouri, U.S.
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    Problem varnishing in corners

    When I make boxes, I usually run into this problem. The varnish seems to not want to stick to horizontal surfaces where they connect to adjacent verticals. I first thought it might be that poly doesn't want to stick to most things, but the attached photo shows an inside corner of a walnut box, using Pratt & Lambert 38 glossy as a wipe-on, diluted 2:1 with mineral spirits. This is the third coat, taking care to put plenty of varnish along the inside corners. It just seems to pull away from the edges as it sets up. Any help?

    Thanks!
    varnish.jpg

  2. #2
    Join Date
    Jan 2017
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    Marina del Rey, Ca
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    Might be glue contamination causing this.
    "Anything seems possible when you don't know what you're doing."

  3. #3
    Agree with Andy. PVA glue is the worst about that.

  4. #4
    Join Date
    Sep 2016
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    Central Missouri, U.S.
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    Nope, there's no glue there. That's a 3/8" bottom panel that sits in a dado to hold it in place. I spot glue in a few places, but not there.

  5. #5
    Join Date
    Mar 2003
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    San Francisco, CA
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    10,304
    I think the fluid finish is disappearing into the dado. Surface tension pulls it into the crack. One fix would be to apply your finish to the interior surfaces before you glue up the box.

    An added benefit to prefinishing like this is that if you do happen to get squeeze-out, it comes off the finished surface pretty easily.

  6. #6
    Join Date
    Sep 2016
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    "Surface tension pulls it into the crack."

    Actually, that term occured to me, but I'm not smart enough to know exactly how it works. I do know that if I keep applying coats (lots of coats) the area eventually gets covered. I guess the dado fills up. Trouble is, I then end up with so much varnish that it looks overdone.

    It also makes sense, in that it doesn't happen on the interior corners, which are glued miters. They're glued shut, no place for the varnish to move to.

    Thanks!

  7. #7
    Join Date
    Apr 2016
    Location
    Tasmania
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    2,162
    It happens when applying finishes too wet. It's best to apply the minimum to cover without it being too wet. Easier to control spraying than hand applying. Cheers

  8. #8
    Join Date
    Sep 2016
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    Central Missouri, U.S.
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    Thanks, Wayne. Makes sense, if it's surface tension. I've been trying to solve it with heavier application. Sounds like less is more, so I'll give that a shot.

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