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I've always used the strongest JD weld epoxy for glue ups rated at something like 5000 psi 'just to be safe' since the only downside was having to wait around 12 hours for curing https://www.jbweld.com/product/j-b-weld-syringe

But recently I saw they have a quick bonding one for wood that's rated at 1800 psi https://www.jbweld.com/product/woodweld-syringe and stated that it actually bonds stronger than wood. That got me thinking and I looked up sheer psi for wood https://www.woodworkweb.com/woodwork-topics/wood/146-wood-strengths.html (and obviously there are a lot of factors that will affect these numbers) and they were around 2000 (again I didn't deep dive into how exactly testing was done).

I also looked up PSI for decent wood glue and titebond 2 is right around 1,800.

So am I wasting my time using long cure epoxy for furniture building and repairs? I can buy 1 minute instant epoxy with sheer PSI of 3000+ is there any downside to switching to it working with wood.

Thanks!

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  • There isn't a simple answer to this because epoxy can be used in multiple ways, e.g. not just as a gap-filling adhesive but actually as a filler (with or without dry filler material mixed in). But for general glueing purposes, yes, a typical 5-min epoxy will do what's required, and it's certainly better than, for example, a joint with so-so fit being glued with PVA or an expanding polyurethane (something done far too frequently). Highly related, this happened to come up in my YouTube feed a couple of days ago: youtube.com/watch?v=DpDKTqnesMI from The Honest Carpenter channel.
    – Graphus
    Jun 5 '21 at 2:10
  • I should mention that you won't gain quite as much time as you probably expect by switching. Although a 5-min epoxy sets in 5 minutes (very approximately) it takes far, far longer to become strong. Many users won't stress a joint for a couple of hours, some wait longer, and no brand can be considered fully cured until ~1 day. I tend to wait 3 hours minimum, and half a day/overnight when it's cold as my workshop is unheated and cold retards epoxy curing (and heat greatly speeds it up, which can be very useful). I've dropped lots of other epoxy tips in previous Answers if you'd like to search.
    – Graphus
    Jun 5 '21 at 2:22
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One chooses adhesives for many qualities, and strength is only one of them. I'd go so far to say that, for most of us, the PSI rating of a bond is not even the most important quality to consider when choosing an adhesive.

(Reducing the entire science and craft of adhesive choice to a few lines in a Q&A site is a fool's errand, and this is in no way a comprehensive discussion of the pros, cons, and uses of these glues. This is for discussion purposes only. For details I always recommend reading the scintillating verbiage on the label.)

Typical PVA wood glue is plenty strong enough for most construction and repair, but a strong bond depends on a very tight fit and good clamping (whether that is done with actual clamps, or glue-and-screw).

Epoxy would be chosen when you need that strength, and you need to bond dissimilar materials, or you need to fill some gaps. Hide glue would be a good choice for gap-filling when you don't need ultimate bond strength (or you want to be able to take it apart easier at a later time). Contact cement would be chosen when you want to permanently display your mistakes.

Cyanoacrylates are excellent for filling small voids or building up damaged material, or when you want to rely on its ability to wick into tight places.

So if your repairs involve tight and relatively clean wood surfaces and you can clamp well, PVA is fine. If you are working with joints that aren't mating well, then other adhesives might be a better choice.

Once cured, any well-chosen adhesive properly applied will make strong bonds that will likely be stronger than the wood around it.

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  • Excellent concise coverage of the topic, bravo.
    – Graphus
    Jun 5 '21 at 2:23
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    Thanks for the great summary, I like this gem "Contact cement would be chosen when you want to permanently display your mistakes." Jun 5 '21 at 3:49

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