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epoxy strength vs cure time

Old 12-10-2004, 04:10 PM
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kamakasi
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Default epoxy strength vs cure time

Is there a increase in epoxy strength vs it's cure time? They only thing I seem to remember is that faster curing epoxies are not water proof.
Old 12-10-2004, 05:38 PM
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Rodney
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Default RE: epoxy strength vs cure time

Yes, the slower curing epoxy forms longer molecular chains as it cures which results in more strength. As to water proofing, cure speed has little or no effect, all are relatively waterproof. note that all epoxies, even the 5 minute cure type, do not gain full strength for about 12 to 24 hours depending on temperature.
Old 12-11-2004, 03:13 AM
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Default RE: epoxy strength vs cure time

I also found that the 5 minute types seemed rather brittle compared to the slower cure types. This is a generalization though as other brands of 5 minute may be better in that regard and some slow cures may be worse.
Old 12-12-2004, 12:06 AM
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Mike James
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Default RE: epoxy strength vs cure time

Yep.

Like most modelers, I've used the hobby store-type 5, 10, 15, 30-minute epoxies from time to time. No denying that if you're in a hurry, they're convenient. But they are completely different chemically, and even the best ones i've used are inferior to longer cure (laminating) resins. I do like the ZAP laminating resin, although I don't use it anymore.

I've been using West Systems stuff for about 15 years, and you can really see the difference around the shop...
Mix any brand of 30-minute epoxy, use what you want, and leave the excess in the cup. (We use nylon cups, and re-use them when the resin is cured and will pop out.) As Bruce said, the faster epoxies will be very obviously more brittle.

Also, if you use the fast epoxies on a plane, just take a look at those joints after a few months. The resin is starting to change color, and often will shrink away from joints entirely. (and around glow fuel... even worse.)

The good laminating resins, on the other hand, make better joints, don't shrink as much, don't become brittle, and age much better. Today, I'd rather use a good epoxy and wait, than use the fast epoxy.

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