Thread: 1 Resin : 1 Hardener = Epoxy Glue

It is not usualy that exacta science, but if by some chance you got a little more hardener in it may have gone off quicker. Temperature and humidity also have a lot to do with curing times. If you normaly use it at night after work it may take 2 hours to go off but if you have glued up your bench on a hot humid afternoon it could go off very quickly. Good luck.

Epoxy sets by chemical reaction between the resin and the hardener, so manufacturer-specified ratios should be strictly followed. With resins that set via catalysts (polyester, vinylester), you can vary the set time by varying the amount of catalyst used.

As mentioned in the earlier post, one possibility ambient temperature, another is the temperature of the mix. The chemical reaction resulting from mixing the resin and the hardener will generate heat, usually not noticeable when mixing small amounts, but for larger volumes the heat can be significant and will speed up the reaction. I recall mixing up a batch of West system epoxy once in a small metal container, and burning my fingers when I picked it up after about 5 minutes, and a couple of minutes later the mix was rock-solid.

What Greg said. Most epoxies I've used have a disclaimer on the can, along the lines of the weather may alter the drying times.

At 1:1 you can expect "about" the time they refer to on the can. More hardener = quicker drying time, less = slower. On hot days I've used slightly less hardener to give myself longer working times, but I won't add more.

I also believe that the hardness/brittleness of the final result is affected by the ratio and the recommended 1:1 gives the best results, although I think you'd have to stray to a 1:2 or higher mix before you'd notice it without lab testing.

Originally Posted by Claw Hama

It is not usualy that exacta science, but if by some chance you got a little more hardener in it may have gone off quicker. Temperature and humidity also have a lot to do with curing times. If you normaly use it at night after work it may take 2 hours to go off but if you have glued up your bench on a hot humid afternoon it could go off very quickly. Good luck.

Originally Posted by Greg Hawthorne

Epoxy sets by chemical reaction between the resin and the hardener, so manufacturer-specified ratios should be strictly followed. With resins that set via catalysts (polyester, vinylester), you can vary the set time by varying the amount of catalyst used.

As mentioned in the earlier post, one possibility ambient temperature, another is the temperature of the mix. The chemical reaction resulting from mixing the resin and the hardener will generate heat, usually not noticeable when mixing small amounts, but for larger volumes the heat can be significant and will speed up the reaction. I recall mixing up a batch of West system epoxy once in a small metal container, and burning my fingers when I picked it up after about 5 minutes, and a couple of minutes later the mix was rock-solid .

Thank you for the clarification & more expl. of the chemical reaction . In fact, I'm aware of those aspects and always consider them while dealing with epoxy.
I haven't used WEST system epoxy though, but I'll make sure to 'watch out' for the heat when using metal container

Originally Posted by Skew ChiDAMN!!

What Greg said. Most epoxies I've used have a disclaimer on the can, along the lines of the weather may alter the drying times.

At 1:1 you can expect "about" the time they refer to on the can. More hardener = quicker drying time, less = slower. On hot days I've used slightly less hardener to give myself longer working times, but I won't add more.

I also believe that the hardness/brittleness of the final result is affected by the ratio and the recommended 1:1 gives the best results, although I think you'd have to stray to a 1:2 or higher mix before you'd notice it without lab testing.

Great info Skew !!!
This kind of info that I'm after. From your explanation,

1. Do you mean that we can 'adjust' the mixture ratio slightly to obtain certain curing time without worrying of the glue strength??
2. "In term of brittleness, 1:2 mixture is the max tolerable ratio". Am I right??

Once again many thanks for those great reply!

Originally Posted by hcim

1. Do you mean that we can 'adjust' the mixture ratio slightly to obtain certain curing time without worrying of the glue strength??
2. "In term of brittleness, 1:2 mixture is the max tolerable ratio". Am I right??

There's a little bit of leeway, yes. I'm not anal about measuring mL for mL, but in general my mixes are still about 1:1. For longer drying time, I'll skimp a bit on the hardener, using about a 9:10 mix instead. A little bit can make a BIG difference.

1:2 is too far... I was being a bit tongue-in-cheek there. What I meant was that it'd be some ratio like that - which'd be unworkable in practice - before you'd notice any degradation of it's character once it does go off.

For woodworking use, that is. For fibreglassing or similar where strength or flexibility are critical, then you'd notice the difference much earlier.

i've seen it before where epoxy potting compound was not mixed in the correct quantitys and never dried at all.