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Thread: Hysol bonding to varnish

  1. #1

    Default Hysol bonding to varnish

    Hello,

    I’ve received my kit and I’m reading through the instructions in preparation for the start of my build. I’ve done a lot of reading in here about Hysol and Varnish. It seems to be the consensus that Hysol doesn’t bond well to varnished pieces. I’ve ordered the quick build STi wings, I’ve come across a section in the manual about installing the Main rib, a web filler rib and a transition rib. The instructions state to “Varnish each of the #1 rib pieces separately prior to installing on the wing spars.” Therefore I would like to think that Hysol will adhere to a varnished piece of wood.

    I’m happy to hear any comments from those that have completed this step.

    Thanks

  2. #2
    taff's Avatar
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    Default Re: Hysol bonding to varnish

    Varnish?
    What varnish is it?
    If it's EV 400, then sand it at the areas that are going to be bonded.
    Hysol sticks to other things other than wood, why shouldn't it stick to a top quality cured epoxy like EV 400.
    Make sure that the epoxy is fully cured before sanding.

    Not sure if this is possible.
    Maybe you can "varnish" the main rib. But avoid coating the bare wood areas that will later be in contact with Hysol.
    After the adhesive cures, then touch up with EV 400.
    Completed my Classic 4, May 2003. It had std wings. speedster tail.
    912 UL Rotax. Sold to a person in Spain.

    Completed a Skybolt December 2018

  3. #3
    Senior Member
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    Default Re: Hysol bonding to varnish

    I just finished the rib 1 stack a couple weeks ago and if you don't varnish them now, you won't be able to later. Same reason you install the flaperon brace now on rib 1 instead of getting it all together. I can't tell you it's better without varnish but the Hysol sure seems to have adhered to the rib stack just fine. I would also note something I learned about doing at least the main rib of the stack with the wing installed on the fuselage. While it doesn't call out in the instructions to have the wing mounted, I got lucky and ducked the bullet when I did the left one not installed. Others before me noted that they were not so lucky and installing the rib flexed the spar just enough that when they went to mount the wing, it would not go. They had to "surgically remove" the rib and I guess that wasn't a fun job. Best of luck with the build. Varnishing is like watching grass grow but other than that - it's been fun.
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  4. #4

    Thumbs up Re: Hysol bonding to varnish

    Thank you Taff & Geek for the inputs. When I began my horizontal tail section I installed the ribs using the Hysol, then varnished them afterwards using the EV 400. I don’t think there was anything wrong with using this method but it was more difficult getting into the tight spots where a rib fell close to a parallel, metal framing member. I think moving forward I may apply the varnish first, then sand to scuff it and apply the Hysol to ensure a good bond. I have yet to begin the ribs in the vertical tail section so I think that will be a good time to test my theory.

    I have not yet began the rib 1 stack that Geek is speaking of however I’ll be sure to pay special attention to that and fit the wings prior to Hysol to ensure a good fit and not having to perform any surgery. I don’t think I would make a good Doctor, but a better mortician.

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