How much pressure to use when clamping wood together with epoxy/silica glue?

Discussion in 'Boatbuilding' started by mariobrothers88, Dec 10, 2020.

  1. mariobrothers88
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    mariobrothers88 Senior Member

    Hi guys I am about to glue the 1"x3" timbers to my bulkheads using epoxy/fumed silica. I was wondering how much clamping pressure to use: none to barely any pressure, light pressure, or moderate pressure?

    Thanks in advance guys!
     
  2. bajansailor
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    bajansailor Marine Surveyor

    I am thinking very little - surely you only need enough to hold the two pieces together?
    If you clamp them too tightly, you squeeze all the epoxy out.
    Make sure that you 'pre-prime' the surfaces first with a coat (or two) of epoxy, before applying the epoxy to join the parts together.
     
  3. DCockey
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    DCockey Senior Member

    Sufficient to keep the pieces in place and ensure the epoxy is evenly spread up and doesn't run out, but not so much that all the epoxy is squeezed out. Epoxy, partricularly filled epoxy is very tolerant of variation in clamping pressure.
     
  4. mariobrothers88
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    mariobrothers88 Senior Member

    Thanks Bajansailor I definitely won't forget to preprime the wood :)

    How many hours is the minimum amount of time I should leave the clamps on? 8 hrs? 12 hrs? 24 hrs? Thanks in advance for all the help!!!
     
  5. fallguy
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    fallguy Senior Member

    When you see squeeze out; stop clamping.

    For critical areas, like a beam; you can also use 1708 which can't compress. But build the beam to Richard's spec.

    clamping overnite is best, but make sure temps are above 60 or low temperatures will retard cures

    wirking outside; you also need to familiarize yourself with amine blush and mitigation and fixing it
     
  6. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Question: How much pressure to use when clamping wood together with epoxy/silica glue?

    Answer: Less than you think.
     
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  7. fallguy
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    fallguy Senior Member

    Also, when you see the squeezeout; you want to trowel it out. Get a metal trowel and use it elsewhere, but do not squeeze beyond the initial squeezeout to save epoxy or you can make a weak joint.

    The ideal epoxy joint is about 0.040", but this is subject to some scrutiny.

    If you are laminating curved timbers; getting to one millimeter may result in voids in the lamination as you oversqueeze here or there. Sometimes 1mm is not practical is all.

    But the ideal goal is 1 millimeter.
     
  8. ondarvr
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    ondarvr Senior Member

    Adhesives frequently have glass beads added (not hollow spheres) of the exact diameter for the best dimension for the adhesive being used. It can vary from one type of adhesive to another.

    When clamped, the parts will have the correct gap for that adhesive.

    On wood it's a little trickier because you could still apply too much pressure and force the beads into the wood. But it helps.
     
  9. missinginaction
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    missinginaction Senior Member

    All good advice. One aspect of this that I always had trouble with was the parts sliding around once the resin was applied. I learned to drill a few small holes in the parts. 1/16th of an inch or smaller depending on the drill bit I had laying around. Dry fit the parts and tap a finishing nail into the hole and into the second of the two pieces you're gluing. Slather everything up and then slide the parts around just a bit until you can feel the nail(s) drop into the receiving hole(s) you made. Just tap them in lightly. Now you can lightly clamp the piece as others have said and not worry about your parts sliding around. Once the resin has kicked off you can easily remove the little nails with a pair of pliers and a twist. Put a drop of resin in the little hole and you're done.
     
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  10. fallguy
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    fallguy Senior Member

    Very important on vital parts like beams and transoms. Even more so for parts under vac as once the bag is closed; there is no adjusting.
     
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