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I'm working on my first major glue up, and I noticed a failure to bond properly along the edge of the outer board, see picture below. I did some research, and I can think of a number of things I did wrong that caused this -- not enough glue, not using scrap pieces to spread out the pressure, not using freshly worked faces, working too slow, etc. My question is, what do I do now?

Do I simply try to pour more glue into the cracks, clamp is again, and hope for the best?

Do I try to drip denatured alcohol into the cracks, to soften the glue and pry it apart, then try to glue it up again?

I don't have access to power tools, so simply cutting off the offending board on the table saw and starting again isn't really an option for me.

enter image description here

Kravaros
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    Your last sentence is really the correct solution - ripping the glue line and trying again. Despite appearances, it probably is a very strong joint. If you're going to paint it, you could fill that gap in a number of ways. But they won't look great for stained finishes. – CoAstroGeek May 12 '19 at 21:13
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    You seem to think that you would need to have a table saw to rip that board off, but to me this looks like it would be pretty quick work to rip with a hand saw. Since there's already such a big gap the saw should track pretty well, and you don't have to remove a full kerf's-worth of material. In fact, this is a classic technique to joint two boards together without planing them...you just put them next to each other (without glue, though) and cut through the joint. – SaSSafraS1232 May 13 '19 at 16:01
  • @SaSSafraS1232 I'm leaning towards that more and more, but at this point I honestly don't trust myself to cut anywhere close to a straight line for more than a few cm. – Kravaros May 14 '19 at 12:00

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You're in luck here in that this is just with the edge board, it would be worse if it were one of the joints somewhere in the middle. It's hard to be sure from just the one pic but it does look like a couple of the other joints aren't great either which is sort of to be expected, but lots of not-very-good glue joints1 give decent enough service so this could be no problem.

Do I simply try to pour more glue into the cracks, clamp is again, and hope for the best?

Obviously you know this would be a ghetto fix and anyway this won't work. The existing dry glue in the gap will physically hold the two surfaces apart and prevent a good glue joint from subsequently forming.

Do I try to drip denatured alcohol into the cracks, to soften the glue and pry it apart, then try to glue it up again?

This is a reasonable idea but DA is the wrong solvent.

So, what to do now?
As bad as this looks and as weak as it will be (relatively) you may be able to get away with it depending on what this is for.

If you really want to get this off you can take advantage of this being a weak joint and just prise the two pieces apart. One or two flat-head screwdrivers or a couple of hardwood wedges would probably do the trick without too much difficulty. Bear in mind the amount of effort needed to get a lot of dried glue off the edges once you do separate them, this can take a lot more work than you anticipate if you don't have the right tools on hand.

So if you end up just leaving it you have a good number of options for filling the crack. If it's only visible on the underside I'd just ignore it, nobody else will know it's there and out of sight you'll probably forget about it yourself eventually.

For next time

  • Work in subassemblies if you can't get this many glue joints done quickly enough.
  • Have everything ready to go before even uncapping the glue. This should include having the clamps, at least the major ones, lined up and opened to the appropriate width for the glue-up being done.
  • Work out a way to spread your glue faster2.
  • More clamps or stronger clamps, and tightened harder.

1 Arguably the majority of glue joints done by weekend warriors and leisure woodworkers aren't as strong as they could be due to two factors. The first is because of the widespread, but largely mistaken, belief that clamping too hard can lead to starved joints. The second is that PVA is the most widespread glue used in woodworking and this requires high clamp pressure to achieve a strong joint!

2 Rollers are good. A notched plastic spreader can work well too, old credit cards or store debit cards are great candidates for conversion to spreaders (useful for both glue and some finishes).

Graphus
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I think Graphus's answer is pretty much right on, but I want to give you another alternative in case you're not interested in tearing the whole thing apart.

You could reinforce the joint with a gap-filling adhesive, such as epoxy. Unfortunately, I don't think you'll get a good bond to the dried glue surface, so I think you'd have to remove it somehow.

I think the easiest way to get a fresh surface would be to drill holes slightly bigger than the gap every few inches along the failed joint. Then get a good two-part epoxy (I like Entropy or West brands) and use a disposable syringe to "inject" it into the holes.

If you want it to look nice use enough epoxy to make the whole thing flush. Depending on the filler you use you might also want to tint the epoxy with some dye. If the gap goes through to the bottom of the piece you will need to cover the joint with tape beforehand so the epoxy doesn't just run through.

SaSSafraS1232
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Woodworking is an art and a science.

With the amount of glue you have in that joint, it's more likely that the wood will break instead of the glue joint failing. There is no reason to remake this.

manual annotation

I manually annotated this image to show where the glue joint has closed. It looks like the glue joint is only 44% closed. % closed = green_area / (green_area + red_area). Wood glue has a holding strength of 100-300 lbs/sq-in in soft wood. Several square inches of this glue joint have closed, so it should be much stronger than the two wood pieces that it joins.

What do I do now?

Make it look better. Mix wood glue and sawdust. Push the mixture into the joint. Use a hand-plane or sandpaper after the mixture dries.

Stephen Meschke
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    I don't think I really agree with the idea that this will be a full-strength joint. PVA glues are NOT gap-filling. In fact, they typically require quite a bit of clamping pressure (100-250 psi per manufacturer's specs for Titebond 3, for example). Depending on the usage of this piece it might be strong enough, but it will NOT be as strong as a properly glued-up joint. I'd say it's fine as part of a butcher block supported by cabinetry, but I'd be very hesitant to mount hardware or legs to the last board alone. – SaSSafraS1232 May 13 '19 at 21:41
  • @SaSSafraS1232 My point was that the strength of the glue joint doesn't matter, as long as the glue joint is stronger than the wood pieces that it glue together. – Stephen Meschke May 13 '19 at 21:45
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    Right, but my point is that if this whole joint looks like the section in the photo the glue joint will not be stronger than the wood pieces that it glues together. If this is in an application where significant strength is required (i.e. the front edge of a workbench) I'd cut it apart and redo it. – SaSSafraS1232 May 13 '19 at 21:57
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    To add to what @SaSSafraS1232 is saying, it is not correct to state that the glue is stronger than the wood. The joint is stronger than the wood if properly glued. For PVA glue, that includes surfaces jointed flat, using enough glue, and clamping the joint with the appropriate amount of clamping pressure. – Katie Kilian May 14 '19 at 04:56
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    Wood glue is not stronger than the wood itself, as addressed in a number of previous Answers. Good glue joints are, but that is not saying the same thing at all. "the strength of the glue joint doesn't matter, as long as the glue joint is stronger than the wood " That is actually true but the whole point here is that the part of the joint visible in the pic will not be, it'll barely be held together. "glue two pieces of scrap wood with just a few drops of glue and test its strength" If you're clamping firmly sure, but do that leaving a ~2mm gap between boards and see how it goes! – Graphus May 14 '19 at 07:20