Chris Schwarz's Blog

Bound Up On the Topic of Glue

I have never used the right amount of glue , well that’s the way everyone else sees it.

Whenever Publisher Steve Shanesy comes in while I’m gluing, he’s bound to make a comment that I’ve got too much glue on a surface. My reply has always been: Better too much than too little. I’ve never had any finishing problems relating to glue squeeze-out (a great benefit of handplaning your panels) and I haven’t had any joints fail.

Other glue experts would say I use too little glue. I rarely wet both surfaces of a joint (though I’m trying to change my ways on that). I prefer to apply it fairly liberally on one surface then work quickly to get the two surfaces together, especially when I’m using yellow glue.

On Friday we laminated the pieces for the legs on the new LVL workbench. The photo above shows about how much glue I use to join these two surfaces, which make up about 155 square inches on each face.

I poured out a thick bead from the bottle (no fancy glue bottles here) then used a scrap of thin wood about the size of a credit card to trowel the glue to a thin layer. Then I quickly put the two parts together and got a clamp on the lamination at the center.

In the end I looked for a bead of glue squeeze-out at the seam that looks like water beads arrayed on a spider’s web.

Actually, in the end I’m looking for joints that won’t fail. So far, so good.

In the coming days we’ll cut all the joinery for this bench using one setting on our table saw with a dado stack. Then we’ll start bolting it together.

One promising sign that this is going to be a good bench: The 2-1/2″-thick top came out quite flat, stiff and gap-free. And people in the shop are already starting to work on it.

- Christopher Schwarz

8 thoughts on “Bound Up On the Topic of Glue

  1. Joon Orione-Kim

    Kevin,

    The difference between LVL and traditional ply is that the plys in LVLs are not placed on bias to each other. The grain all runs in the same direction basically. Because the veneer is rotary cut, it still has more potential for tearing out than lumber, but you are not dealing w/ endgrain milling like you would when edging baltic birch plywood. The endgrain is the reason that your jointer blades are trashed after running the plywood over it.

    In theory the glue content in the LVL is going to be more abrasive than just wood, but as to how much more abrasive, I don’t know that anyone would be able to speak empirically on the subject.

  2. Kevin Doyle

    Chris/Megan,
    This is a cool to see this project. I’ve seen Norm A. using LVL a few times for shop furniture, but not like this. I’m a precision engingeer and I am really excited to see how this works out since this material will be stronger and more stable than just about anything else available. I am especially interested in the tool life during fabrication. I’ve seen my HSS jointer blades scared after edging a few lengths of 3/4" baltic birch ply. Keep the posts coming.
    Kevin

  3. Sean

    Jeremy,

    I haven’t done the experiments, but the stuff you mention about tenons makes little sense to me. I always thought the main strength of the Mm&T came from the long grain bond between the tenon cheeks and the sides of the mortise. All the other mating surfaces are end grain to long grain, and as such, much less strong.

  4. Sean

    Like most things, it depends. Gluing up a benchtop, the only problems that come from using too much glue is that it makes a mess and can make the pieces slide around a lot before aligning. But there are times when using only as much as necessary can sure save you some work and keep you finish from being marred by those horrible glue resist patches. For example, I was working with some cherry and was gluing in a strip of wood on the inside or a carcase to act as a stop for the inset door. I wait until the door is hung to do this, so that I can position the strip exactly. Anyway, if I use too much glue in an instance like this, positioning is harder (the sliding again) and clean up is not easy as clamps are needed to hold the piece in position while it sets – thus wiping away is difficult to impossible. I suppose I could wait until the glued gelled and scrape it off, but I find this hit and miss with ungelled glue underneath just underneath the skinned over part and it just generally being a technique that does not guarantee that some glue won’t stay in the pores. If glue does get in the pores, one now faces the nightmare of scraping and sanding enough to get below it. Much easier to just calibrate the right amount of glue in the first place. The main thing in this instance was to make sure that I wiped the excess from the edge areas so that as the glue from the middle spread, it filled these spaces rather than beaded out.

    YMMV

  5. James C

    I’d have to agree with using more, rather than less, glue on a joint. I once had a person at a woodworking course ask me why I used so much glue. I explained to him that it was easier to remove the excess that spilled out than to add extra later.

    James

  6. Jeremy Kriewaldt

    A similar discussion occurred on The Wood Whisperer a few weeks ago:
    http://thewoodwhisperer.com/how-much-glue/

    As you can see from this, I found a most enlightening discussion of gluing and the difficulties thereof in J E Gordon’s book The New Science of Strong Materials. That book and the companion (Structures) are worth reading in their own right but the insight on gluing is very useful.
    Most of the strength of a glue joint is at its edges – the stuff in between is a passenger that contributes nothing except weight. Some runout is better than a starved joint if that means that you have a bead of glue along the whole of the outside lines of the joint. Sometimes this is going to be hard to achieve but think of a mortice and tenon joint. The ideal is to get a thin but complete glue line along:
    1. the 4 longitudinal corners of the tenon where they meet with the corners of the mortice and
    2. the four outside corners of the shoulders of the tenon where it meets with the face into which the mortice has been cut.

    The first is easy – spread glue on the 4 inside corners of the mortice (no need to go all the way to the bottom) and the longitudinal corner edges of the tenon. For the second, I find it best to put glue on the 4 tenon shoulders. You can be a bit more generous on the tenon edges and in the mortice than on the shoulders – you should push any surplus to the bottom where it will do no harm. Be more careful on the shoulders and try to get more of the glue on the outside of the shoulders than the inside to reduce squeeze out while still getting a complete bead of glue along the outside of the shoulder/face joint.

  7. dave brown

    Chris,

    I hope you get all these issues that keep you bound up out of your system before you start work on your Chinese stool again.

    Have you tried a good dim sum?

    regards,
    Dave

  8. Bill

    I was at a professional cabinetmaker’s shop a few weeks back and he had made himself a huge wood-bed lathe, with the ways made up of laminated 2x10s or something about that size. I asked him how the heck he laminated such big hunks o’ wood together and in explaining his process, he told me that when he has to do big surface-area glue-ups like that, he buys those cheap plastic tiling trowels, with the fine v-notches and uses those to spread the glue around. He said he finds it leaves behind just the right amount of glue and makes it very fast and easy to spread it all out and get everything covered, and once it gets caked up, he just tosses it, because they’re only about a buck a piece or something.

    I thought that was a useful tip.

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