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Thread: Best glue for failed joint

  1. #1
    Join Date
    Jul 2010
    Location
    Rockland, ME
    Posts
    205

    Best glue for failed joint

    Hello,

    I have a mitered joint in solid hardwood that has partially failed. The piece is a case with a long 23" mitered joint, reinforced by Dominos. I was clamping one side of this case to another identical case and used too much clamping force. About 1" of the miter joint separated. The rest of the joint seems very solid -- it's just a small portion of the glue line(end grain to end grain) split. There's a very fine gap. What glue should I use to repair this? The PVA wood glue I used originally doesn't seem to be the right choice. Especially since I'll essentially be gluing glue to glue. What do you think? A gap filling CA glue? Gorilla Glue? I've never used epoxy before(and don't actually have any)...would this be best?

    I'd love to hear as much advice as possible.

    Thanks!

  2. #2
    As far as I know, the only glues with any reasonable adhesion to cured PVA are epoxy and CA, and of those CA seems to be best. How much gap do you actually have? It sounds like the joint didn't fail but you actually clamped it wrong and it dried like that, and now you need to fill the gap? If it's a dominoed joint, without looking at it my first thought would be that you're getting minimal strength from the miter anyhow, compared to the dominoes, so maybe just treat it as a cosmetic flaw. Maybe some sawdust and thin CA to fill some of the gap, and then wood filler to hide it as best as possible.

    Or am I reading the situation wrong?

  3. #3
    Join Date
    Jul 2010
    Location
    Rockland, ME
    Posts
    205
    Thanks, John. Yes, you're right, the joint didn't really fail. At least not fully. Like you said, it's more of a small cosmetic flaw. The gap definitely wasn't there originally -- I saw and heard it split when clamping the side of this case to another. The Dominos are definitely what is doing most of the work holding the joint together, but my fear is that this split (probably about 1/64" at its widest on the inside of the miter) might grow and create other cosmetic problems. Which, of course, I'd love to not happen if I can hold the split together with glue.

  4. #4
    Join Date
    Dec 2003
    Location
    SF Bay Area, CA
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    15,332
    Polyurethane glues stick to just about anything but you just want to fill the gap? Why not glue in some small wedges/slivers of the same wood to help hide it? Epoxy will work and likely the poly will work, too.
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  5. #5
    Join Date
    Jul 2010
    Location
    Rockland, ME
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    I'm actually really worried about the broken glue line spreading down the rest of the miter. And a little about the overall integrity of the whole joint(although wi the Dominos, I probably should t be.) What I'd like to do is put a little glue into the 1/64" gap that opened on 1" of the joint, clamp it, and hope it never opens up again. CA would be the easiest for me, and as John mentioned would do a good job of bonding to the cured PVA I originally used in the joint, but I fear it might be too brittle of a glue. That it might just crack down the road.

  6. #6
    Join Date
    Sep 2013
    Location
    Wayland, MA
    Posts
    3,655
    Go for the dutchman. Widen the crack out enough to get a piece of wood in (chisel, saw, or micro router), then pound in a slightly wedge-shaped piece of wood with glue carefully matched for color, grain and grain direction. If you like, while finishing use a fine tipped brush to or pen to carry the grain lines across the repair. Chances are it will be both invisible and a permanent repair, a fat glue line will always look like an error.

  7. #7
    Join Date
    Apr 2008
    Location
    North of Boston, MA
    Posts
    357
    Seems to me your best course depends on the crack.

    If you can push it closed using clamps, then I'd go with CA. It won't fill a gap, but will stick well if you can get the surfaces close. I wouldn't worry about strength. CA is brittle, but that location shouldn't be subject to shock.

    If you can't clamp the crack shut, don't try to glue it. Epoxy is the only glue that likes gaps, but you will make a mess of the adjacent surfaces trying to get epoxy into such a small crack, and epoxy is difficult to clean up. Instead, use one or another of the techniques suggested above to fill it.

  8. #8
    Can you post a picture?

    Given that you used Dominos, I would not be concerned with the structural integrity of the joint; you're just filling a gap. To that end, if the gap is fine enough, I would mix epoxy with a very little bit of sawdust (just to make it opaque) and sand it into the joint. You'll get less of a 'plasticwood' look if you use epoxy vs pu glue or pva + sawdust. CA is fine too, but unlike other posters here, I have found it to have poor adhesion; if the wood moves, it has fallen out of knots on turned objects I've done.

    If the gap is very fine and you're using shellac or oil based varnish as a topcoat, , they you might be able to even fill the gap by sanding in your first topcoat.

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