Question about using epoxy 2 different ways with plywood on frame construction

Discussion in 'Wooden Boat Building and Restoration' started by AwJees, Nov 20, 2021.

  1. AwJees
    Joined: Aug 2021
    Posts: 21
    Likes: 2, Points: 3
    Location: Beoit Wi

    AwJees President of He-Man Woman Haters Club

    This question is a result of reading a lot of posts about epoxy use and assembly of wooden boats. My boat is a 22 foot Carolina dory, plywood on frame. First method is to simply apply epoxy to bare wood surfaces being joined and then screw in place. Flip the hull and epoxy the inside. Second method is to encapsulate frames in epoxy first. Set them up on the strongback and temporarily screw plywood in place. Get the fit right and cutting done.
    When ready to put plywood on permanently remove temporary screws and epoxy the inside of the plywood fill screw holes with thickened epoxy and screw back in place. This means I will be joining a wet epoxy to a cured epoxy surface [ the frames]. Will I get a good bond this way? Ive read yes and no from other sources. If this works I wont have to epoxy the inside of the hull after flipping. I am disabled and really cant work on my knees so i have to think out how I do things. I trust this forums opinions more than others.
     
  2. fallguy
    Joined: Dec 2016
    Posts: 5,258
    Likes: 1,006, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    It depends.

    Every brand of epoxy has a typical open chemical bonding window; this is called primary bonding.

    After the primary bond window has closed; you must seek to achieve a secondary, mechanical bond. Epoxy is ver strong, but it will sheer off glassy, uprepared substrates easily. Until you don't want it to, that is....he he.

    So, let's say you epoxy coat 6 frames from morning, midday, and nite to get 3 coats of epoxy on them. Then let's say you have an epoxy with a 48 hour bond window. And you get two of the frames installed in that 48 hours. It can technically be done without sanding.

    The other four frames would require sanding with 40-60 grit paper on all surfaces to create a mechanical bond surface.

    I will tell you that I always sand after 24 hours despite my epoxy and a 72 hour bond window.
     
    Sam C likes this.
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