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Thread: glue 1 surface or 2

  1. #1
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    glue 1 surface or 2

    After reading Stephens post where he mentioned gluing both faces of the laminated legs, it got me thinking. I generally avoid that and feel gluing one surface is plenty. I think if I was gluing up a mallet, I might go that extra mile but I'm more of a glue one surface guy. Prove me wrong and I'll change my wicked ways.

  2. #2
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    Applying glue to both surfaces is the example I followed when beginning woodworking. I still usually do it that way more than 20 years later, at least when using PVA glue.

    That said, I did a glue up your way yesterday evening, and I expect it'll be fine, especially since the workpiece spent the night under good clamp pressure.
    Chuck Taylor

  3. #3
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    I think at the end of the day, the amount of glue is what is important, right?

    I just try to use "enough" glue, but not "too much," because "too much" is a huge mess. I usually just put glue on one surface, except when I don't, which is mostly up to intuition and how I feel about how much glue is necessary or not for two given pieces to join up...

    I'm a lot more generous with things like mortises, or anywhere that endgrain is present, while I'm much more conservative with flat, well prepared faces.

    And when I can I don't use glue. I mean, some things just don't need gluing, but we like to glue them anyway. Sometimes it's better not to glue things when considering wood movement or future modifications and repairs. I can't tell you how many times I've wanted to change or fix something that was glued...

    But, I only think I know what I'm doing. I've learned enough to know how little I know, so don't put much stock in anything I say or do! Listen to much smarter and more experienced people instead.
    Last edited by Luke Dupont; 05-04-2022 at 9:48 AM.

  4. #4
    As long as you get enough glue on to saturate both faces plus a minimal amount of squeeze-out gluing one face is fine. The spread rate needs to be heavier than when coating both faces. Double coating ensures no holidays. I definitely glue both faces of mortise and tenon joints as the sliding assembly can prevent full glue transfer from only one surface.

  5. #5
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    It could be that both are right. (with PVA glue)

    If there is enough glue to squeeze out, then applying glue to only one side may have the same effect of glue being applied to both sides of a joint.

    If applying a thin coat of glue to the surfaces it might be better to give a thin coat to both (all) sides of a joint.

    My understanding may be incorrect. This being PVA glue absorbs in to the wood along the joint. When it dries the molecular structure of the dried glue is holding the pieces together as long as there isn't a gap.

    PVA glues are not a gap filling adhesive. Some epoxy glues can be used to bond across gaps.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  6. #6
    Many many years ago an old guy who I was working for told me to spread glue on both surfaces & called it "sizing" the joint ? Never questioned it and continued to "size" every thing I've glued up for last 40 years. Maybe unnecessary but never had a failure just probably wasted a lot glue

  7. #7
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    Quote Originally Posted by Jim Koepke View Post
    It could be that both are right. (with PVA glue)

    If there is enough glue to squeeze out, then applying glue to only one side may have the same effect of glue being applied to both sides of a joint.

    If applying a thin coat of glue to the surfaces it might be better to give a thin coat to both (all) sides of a joint.

    My understanding may be incorrect. This being PVA glue absorbs in to the wood along the joint. When it dries the molecular structure of the dried glue is holding the pieces together as long as there isn't a gap.

    PVA glues are not a gap filling adhesive. Some epoxy glues can be used to bond across gaps.

    jtk

    Would you do anything differently with hide glue?

  8. #8
    I've done it both ways. It doesn't matter in my experience.
    I pay way more attention to the flatness.

    In fact, there is an argument to be made that doing one surface only, then smooooshing the two surfaces together and witnessing how well the transfer coverage is on the other piece is evidence that your two surfaces are properly mating.

  9. #9
    I was taught to put glue on both surfaces but that always gave me too much squeeze out. A few years ago, I switched to glue on one surface only. Never had any problems with that approach. It saves a small amount of time - the time you'd spend putting glue on the other surface.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  10. #10
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    I always do that.

  11. #11
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    I only glue both sides when gluing end grain. On the end grain piece I put glue on and rub it in good with my finger. I than glue the other piece and go back to the end grain piece and put a little more on before making the joint up. Doing the end grain this way was what I learned as sizing. Try it for yourself. Put some glue on end grain spread it, let it sit a minute or so and look again. It will look dry especially on open pore stuff like oak.
    Jim

  12. #12
    Quote Originally Posted by Kevin Jenness View Post
    As long as you get enough glue on to saturate both faces plus a minimal amount of squeeze-out gluing one face is fine. The spread rate needs to be heavier than when coating both faces. Double coating ensures no holidays. I definitely glue both faces of mortise and tenon joints as the sliding assembly can prevent full glue transfer from only one surface.

    +1
    I apply glue (PVA) to both mating surfaces. I prefer to see the glue evenly applied, rather than assuming that full coverage was obtained simply by judging the amount of squeeze out.
    End grain joints can require more glue or a sizing coat to properly adhere, due to the nature of the wood.
    I sometimes think, applying a light coating of glue to both sides rather than a heavy coat on one side uses less glue in the long run. That's just a WAG

  13. #13
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    I was doing a lamination on those legs, and used a roller to moosh the beads out...

    M&T joints: Coat the tenon.

    Gluing up a flat panel, like for a table's top....one bead down one edge...then "rub" the 2 parts together, until I feel it begin to stick..

    Dovetail Joints: I brush on glue to the half that is sliding into the joint...but not the other half...
    A Planer? I'm the Planer, and this is what I use

  14. #14
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    Quote Originally Posted by Luke Dupont View Post
    Would you do anything differently with hide glue?
    Not having ever used hide glue my answer to this could be meaningless.

    Though isn't that how a rubbed joint is put together?

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  15. #15
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    Quote Originally Posted by Richard Hutchings View Post
    After reading Stephens post where he mentioned gluing both faces of the laminated legs, it got me thinking. I generally avoid that and feel gluing one surface is plenty. I think if I was gluing up a mallet, I might go that extra mile but I'm more of a glue one surface guy. Prove me wrong and I'll change my wicked ways.
    What kind of glue? What does the mfgr recommend.

    I recently used System Three T88 epoxy when edge-joining 1 bubinga/guatambu/walnut. The instructions were clear to apply epoxy to both surfaces and dont over-clamp.

    The actual effectiveness of the joint with glue on one or both surfaces might depend on the wood species and surface prep.

    You could test this. Prepare a number of pairs of test pieces, perhaps 4/4 about 2x2 or so, prep the edges and glue/clamp with both methods. Id prob make at least 4 or 5 tests for each method. After an appropriate amt of time hold one half in a vice and smack the other with a hammer or apply some other force. (I might use a big wrench for a non-impact force.) See if one method holds better. For a more complete test repeat with other species, perhaps combinations.

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