Five minute epoxy isn't

[Brian Kent]

I usually leave epoxy to dry overnight or all day.

So in a time where I needed to believe "Five minute" epoxy, I found out that after 5 minutes it is a little bit tacky. Just curious how long it will take to hold up the tail of the poor broken ceramic bird on top of the cookie jar. (grandson doesn't want grandma to be sad.)

62°

[Reed Gray]

I prefer 24 hours, no matter which glue I use.... Safer that way...

robo hippy

[Dennis Ford]

It is very temperature sensitive, sets fast at higher temperatures, takes what seems like forever when cold.

[Ken Fitzgerald]

It can depend on the amount of hardener added too! Too little can sometimes prevent it from setting up at all.

[John K Jordan]

I believe the 5 minutes indicates the WORKING time. The cure time is longer.

From one 5-minute epoxy instruction:

"Cure time for 5-minute epoxy is 3/4 to 1 hour for a functional cure. Full bond strength is reached in 16 hours. "

When I use epoxy I test the tackiness of what is left over on the mixing surface to know when the epoxy in the joint is hard enough to be moved if needed, but always wait at least overnight before stressing it.

Of course, things go down hill when the shelf life is exceeded. I like to write dates on things.

JKJ

[Brian Kent]

Thank you all.

[Larry Frank]

Just an additional thought. I had some issues with 5 minute epoxy when making small amounts likely due to not getting amounts correct.

I bought a cheap electronic scale and now weigh the amount and it has worked much better. I weigh it and mix it in the small pill cups that I found really cheap.

[John K Jordan]

Just an additional thought. I had some issues with 5 minute epoxy when making small amounts likely due to not getting amounts correct.
I bought a cheap electronic scale...

That's a good idea - I have good scales but never weighed. I generally squeeze out two parallel tracks of resin and hardener then mix.

My favorite way to mix just a little epoxy for use at the lathe: I stick a short length of 2" aluminum HVAC tape to the lathe bed and mix on that. With the flat tape it is easy to squeeze out equal length tracks to get the amounts right (or close).

JKJ

[Curt Harms]

It is very temperature sensitive, sets fast at higher temperatures, takes what seems like forever when cold.

You're not kidding. I have system3 small squeeze bottles. It was cool so was really thick. Figured I'd put it in a warm (not hot) water bath. That worked, it flowed well. The pot time seemed like about 2 minutes though.

[John K Jordan]

You're not kidding. I have system3 small squeeze bottles. It was cool so was really thick. Figured I'd put it in a warm (not hot) water bath. That worked, it flowed well. The pot time seemed like about 2 minutes though.

With the "right" amount of heat you can also get a disastrous runaway thermal reaction with epoxy.

Long ago I ran a small metallography lab and routinely vacuum-potted uranium samples in epoxy in small sample rings, maybe 1-1/2" dia x1" tall. When in a hurry for results, I occasionally warmed the potted sample to accelerate curing. Once I warmed it a TINY bit more than usual. The exothermic reaction was rapid and severe - I was left with a useless dark amber chunk of smoking epoxy, deeply cracked and fissured, with shards splitting off and popping out as I watched!

I suspect this reaction would never occur on a thin layer of epoxy but would need a certain critical volume. I never experimented further; I just took that as a lesson in patience!

That experience was over 40 years ago. Looking today for the first time with Google, I found this little video where this guy's batch of epoxy hit a smokin' 300+ deg F on the surface. No telling how hot it got inside.
http://longezproject.blogspot.com/2014/03/epoxy-104.html

JKJ

[John Terefenko]

I would have went with med. CA Bonds instantly and made to hold things like that very well.

[Al Launier]

What Ken Fitzgerald & Jonn Jordan said.
I believe the mix ratio is absolutely critical for maximum strength. I find it more accurate to mix a bit more than is necessary as I find it easier to make each bead the same height & size. I'll run a bead alongside each other trying to maintain the same size & then cut each to the same length. Plus the extra amount allows testing on scrap pieces to test the hardness & breaking strength rather than test the final product. Also, I've found the 5-minute epoxy to be more brittle than a longer curing epoxy, such as 18 hour epoxy, which I use for making golf clubs.