Two-part epoxy is a resin and a hardener mixed at a fixed ratio. Set times run from minutes to hours by product, and full cure from hours to days. WEST SYSTEM says never to change the ratio to change the speed. Putty is the same two-part idea, kneaded by hand.
Set vs cure
WEST SYSTEM describes three stages. Mixed epoxy starts liquid, and that open time is when all assembly and clamping should happen. Then it gels, firm as hard rubber, dented by a thumbnail. Then it goes solid, at about 90% of its strength, and clamps can come off, though it keeps curing over the next several days.
WEST SYSTEM says a hardener’s pot life is much shorter than its open time. For its 205 hardener it gives 9 to 12 minutes in a 100 gram cup at 72°F, but 60 to 70 minutes in a thin film. Gorilla notes its epoxy warms up as you mix it.
Mix at the maker’s ratio
- J-B Weld Original and KwikWeld, and Gorilla Epoxy, mix 1 to 1. WEST SYSTEM 105 with 205 hardener mixes 5 to 1, and with 207 or 209, 3 to 1.
- WEST SYSTEM says not to adjust the cure time by changing the ratio, and that most curing problems trace to the wrong ratio. It says to stir for at least 1 minute.
- Gorilla says to mix its epoxy about 20 seconds and apply it within 5 minutes.
Each product’s times
| Epoxy | Form | Sets or works | Use or cure |
|---|---|---|---|
| J-B Weld Original | Twin tube | Handle after 4 to 6 hours | 15 hours minimum before use |
| J-B Weld KwikWeld | Twin tube | Sets in 6 minutes | Fully cured in 4 to 6 hours |
| J-B Weld SteelStik | Putty stick | Sets in 5 minutes | Drill after 60 minutes |
| Loctite Epoxy Putty | Putty | Working time 3 to 5 minutes | Functional in 60 minutes; full cure 24 hours |
| Loctite Epoxy Quick Set | Two-part | Gels in 4 to 10 minutes | Usable in 1 hour; full cure 24 hours |
| Permatex 5 Minute Epoxy | Two-part | Sets in 4 to 6 minutes | Usable in 4 hours at 72°F |
| Permatex Cold Weld | Two-part, equal amounts | Sets in 8 minutes | 16 hours before service |
From each product’s page or data sheet. J-B Weld’s KwikWeld page says both 4 hours and 4 to 6 hours; we give the range. J-B Weld says set and cure times change with conditions.
A “5 minute” name isn’t a promise: Permatex says its 5 Minute Epoxy sets in 4 to 6 minutes. Loctite adds that joining parts close to its Quick Set’s set time reduces adhesion.
Putty vs tube or syringe
J-B Weld says its twin tubes, syringes and putty sticks are all two-component epoxies; the main difference is how they’re dispensed. The putty has an outer and inner layer that you knead by hand, wearing gloves, into a moldable mix. Loctite says to knead its putty until the color is even, about 1 minute.
WEST SYSTEM warns that a thick mass of mixed epoxy heats up as it cures, and says not to fill voids or cast layers thicker than 1/2 inch with its epoxy. We’d mix only what you can use in the open time, and wear gloves.
Epoxy or super glue?
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