Can someone describe an epoxy-starved joint?

Discussion in 'Boatbuilding' started by OrcaSea, May 7, 2015.

  1. OrcaSea
    Joined: Oct 2014
    Posts: 100
    Likes: 1, Points: 18, Legacy Rep: 17
    Location: Arlington, Wa

    OrcaSea Senior Member

    I have decided to do some structural re-building on my little 16' sailboat restoration job, and other than some small repairs I have not done any major structure building with epoxy & wood. This repair involves the keel and replacing the bedlog and sections of the keelson and I want to make sure it is strong.

    I am used to wood glued joints (clean & tight) and understand it is a little different for epoxy? So, I have questions, like, can you use fasteners with epoxy in structural joints, or will it squeeze-out too much of the goo? Stuff like that.

    Thanks!

    Curtis
     
  2. TeddyDiver
    Joined: Dec 2007
    Posts: 2,578
    Likes: 120, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Few basic things. Precoat the both surfaces with unthickened epoxy. This will prevent the starvation just use slower epoxy formula that it won't kick-in too fast. Be sure it's still wet or tacky when you apply the thickened (pref.with microfibers) epoxy on the other surface. Set parts together. You can use fasteners but they are just to keep the parts lined and in contact so that all the way of the joint some of the epoxy squeezes out. If you need some bolts or big screws in some places they are easy to put in place after the glue has allready hardened.
    BR Teddy
     
  3. upchurchmr
    Joined: Feb 2011
    Posts: 3,051
    Likes: 149, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Any glued joint works best with a minimal thickness of glue.
    .005" was what I was taught.
    Epoxy is the same, it just allows more gap than others with less loss of strength.
    So long as there is no voids, which is what Teddy is talking about how to avoid.
    The unthickened epoxy is to insure the glue penetrates as much as possible into the wood (which is not very far and often over claimed).
    If you squeezed the glue out (for example to .001") the joint would also have less strength.
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 475, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The joint needs some gap, for epoxy to do it's job, so if it's under a fair bit of pressure during assembly, you can literally squeeze out the goo, leaving the joint starved. I run into this on laminations, where I'm applying a lot of pressure to make the pieces conform to the shape of the jig. To prevent starving the joints, I lay a length of monofilament in the wet epoxy, as I'm assembling the joints. This serves to keep the joint open enough to allow the glue to have a place to live.
     
  5. OrcaSea
    Joined: Oct 2014
    Posts: 100
    Likes: 1, Points: 18, Legacy Rep: 17
    Location: Arlington, Wa

    OrcaSea Senior Member

    Thanks, guys, I appreciate you taking the time to advise : )

    I imagine if the mating surfaces are left clean but slightly rough that will allow some space for the goo as well as some tooth to grip on to.

    Thanks, again!
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 475, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The trick with epoxy is to bring the mating surfaces together, just enough to touch. You can even back cut the non-visible portion of the joint to offer some goo room, yet have a razor tight seam exposed.
     

  7. pauloman
    Joined: Jun 2010
    Posts: 268
    Likes: 10, Points: 18, Legacy Rep: 151
    Location: New Hampshire

    pauloman Epoxy Vendor

    one of my customers adds some fine ground walnut shell (used for non slip) into the epoxy - this works like a spacer preventing all the epoxy from oozing out if clamped too tight

    paul oman - epoxyroducts.com
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.