Super glue and epoxy are two specialty glues that certainly have their uses. But each of them have some pros and cons that will affect your opinion of them. Is epoxy stronger than super glue? Let’s take a look at super glue vs epoxy and when to use each, so you can get the best results possible from each.
Caveats of super glue
Super glue has extremely high tensile strength, but underwhelming shear strength. That’s why the 1980s commercials for super glue could show a man gluing his helmet to a beam and hanging from his helmet, supporting his full weight. The high tensile strength means super glue can indeed support 200 pounds or more, if the force is strictly up and down relative to the glued joint.
But most real world applications aren’t like that. When you try to glue a broken handle back onto a coffee mug, the force isn’t up and down when you go to use it. The shear strength comes into play at that point. Initially the results look good. You put a couple drops of glue on the mug, stick the handle on, wait 30 seconds, and it seems pretty good. And it’s probably fine the first few times you use the mug again. But within a few weeks, the handle breaks back off because the force is mostly side to side relative to the glued joint.
Super glue works pretty well when you can compensate for its weak shear strength. It works reasonably well on plastic models because the model pieces have pegs and holes that provide the shear strength, while the glue provides tensile strength. The result is a strong joint.
Weaknesses of super glue
Super glue also performs poorly when the pieces don’t fit together tightly. When the repair has gaps, most ordinary super glues won’t stick well. There are special formulations that can deal with gaps better, but they tend to be more expensive and not necessarily sold in the stores you frequent.
It also doesn’t handle low temperatures well. I use that property to disassemble super glued parts easily.
If super glue never worked as well for you as it seems to in that 80s commercial, that’s why.
It is extremely adept at gluing skin though. Which can be a problem. You don’t want to glue yourself to whatever it is you’re working on.
What about epoxy?
Epoxy creates a chemical bond that holds pieces together. Overall it’s a better general purpose glue. The problem is it’s less convenient. You have to mix up the two parts, which always results in some waste, and it takes longer to cure. Super glue cures in 30 seconds, where epoxy takes 5-30 minutes depending on the formulation. The stronger grades take longer.
Epoxy also handles gaps very well. When your pieces don’t fit together tightly, the epoxy will tend to flow into the gaps and fill them. You can contour it with a toothpick before it cures so you get a nice, smooth, tight bond.
I’ve fixed a lot of things with epoxy over the years that I thought stood no chance. In almost every case that you’re tempted to reach for the super glue, chances are you’re actually better off with epoxy, as long as you don’t need an instant repair.
The other disadvantage with epoxy is cost. Super glue costs about 1/3 as much. Sure, the epoxy tube is bigger, but chances are both will go bad before you use it all. Then again, I’ve found it’s generally worth the cost.
If I need a really thin layer of glue to finish a repair, I may prefer super glue. But generally speaking, I probably use epoxy more.
Is epoxy stronger than super glue?
While epoxy’s tensile strength is not as strong as super glue, its shear strength is much better. If you’re trying to glue your helmet to a beam and dangle off it, super glue might be stronger. For most things you’re actually going to want to do, usually epoxy is stronger than super glue. Super glue’s shear strength is 14 PSI vs epoxy’s shear strength of 4,560 PSI. Super glue’s tensile strength is about 4,000 PSI. Epoxy’s tensile strength can range from 2,900 to 4,400 PSI depending on the formulation.
In some situations, super glue may be a little bit stronger. But epoxy is a much more consistent overall performer.
Super glue and baking soda vs epoxy
There’s a trick with super glue to fill gaps. Put some glue where you want it, sprinkle baking soda into the gaps, then it crystalizes into a strong bond. If you need more, just add a bit more glue, then sprinkle on some more baking soda.
It works reasonably well and the result is strong. It seems to compensate for the shear strength at least to a degree. I prefer epoxy, but the glue and baking soda trick works if that’s what you have on hand.