Curing 2 part epoxy in summer humidity

[James Nugnes]

I had to use a two part epoxy to sculpt a tail for a carving as the tail was just too thin to carve without risking breakage. My problem is that at least in this humidity I can't get the epoxy to harden. I made about four tails so I could pick the one I like the best and none of them will cure completely. Should have hardened in 24 hours and I am already up to 48-72 hours and none are hard enough to shape and texture.

Any idea what I can try to speed up the curing process?

[Paul R Miller]

Are you mixing very small quantities? The most common reason for poor cure in epoxies is inaccurate or incomplete mixing. This is not a catalyst reaction like polyester. The components are both consumed in the reaction and in a specific ratio. When mixing very small amounts it is difficult to get exact ratios and the result is that when all the resin molecules have found a hardener molecule to bond with, there are a number of extra molecules remaining in the mix and they will cause problems with the physical properties of the cured product. The best idea for small quantities is to mix more than you need, grit your teeth, and throw away the expensive left-overs.
What ever you do, don't try to add more hardener. This will only make the problem worse.

[Mike Hollingsworth]

how about some heat?

[James Nugnes]

Well, according to instruction I had to put a thin wire running through the tails to shape them. I can probably use a heat gun or blow drying. It would probably take that kind of heat. Is that the kind of heat you are talking about?

I really think I mixed the stuff close to accurate. I even used two different types just to see if there was any improvement.....about the same.

[Paul R Miller]

Be careful with too much heat. The epoxy will become thermoplastic. I didn't mention it because in summer temperatures you should be trying to slow the reaction not speed it up. There is something wrong in the material or preparation.
What ratio is it supposed to be?
What kind of epoxy did you use?
What, if any thickeners or fillers?
How long did you mix it?
How old is it?
I'm grasping at straws here. As a boat builder I've used a great deal of epoxy in a wide variety of situations / uses and this has me stumped. I'll give it some more thought if you can answer the questions and give me a better picture.

[Mike Henderson]

I have to echo what Paul said. In heat, epoxy tends to flash off (harden very quickly and to generate a lot of heat in the process). I use West Systems epoxy. What I'd do is mix one squirt of each and stir it around very well. If it starts to get hot, stick the container in some ice. You may think this is excessive but the epoxy can go off really fast if it starts to get hot.

Make absolutely sure you have the proportions correct.

Mike

[James Nugnes]

One was Milliput and the other is Sculpt. Both call for equal parts. Both are about two years old but remained sealed the entire time as I simply did not have use for them until now.

I have a couple other types that are two part. Maybe I should try yet a third type.

Maybe having chosen the absolute hottest most humid weather period so far this year in the NE is just ripping me up. We have had triple digit temps with well over 90% humidity the last few days and the daytime temps have been at least 90-95+ the entire time with two 100+* days tossed in for good measure. Night temps falling to about 85* (what a break!!).

No added thickeners or fillers. Just a thin metal wire running through a piece about 2.5" long by 3/16" diameter. I mixed for about 4 minutes....having combined it...rolled it out...recombined it, shaped it, added the wire and set it aside to cure.

It is setting up so darned slow I can't believe it.

Whenever I am working with materials like Quik-wood or some sort of epoxy or filler I always set aside some extra and ball it up just to see how the extra is curing separately from the actual workpiece. Oddly enough the balls of epoxy seem to be curing at a somewhat faster rate than the workpieces. They are not completely cured but they are close to it. That has really got me stumped! Could the wire be a contributor to the problem in some sense?

[Paul R Miller]

The age of the material is the best guess I have at this point. Two years could be a problem especially if subjected to extremes in temperature. Doing it on the hottest day should not have caused this. It should have caused the opposite problem. There's no reason for the wire to figure in either. This has to be a material problem. You watched your ratios carefully and mixed thoroughly. You had warm temperatures. There's nothing left to blame it on except the material. You could contact the manufacturer but shelf life can be an issue with epoxy.

[James Nugnes]

I had some Tamiya two part around and it cured overnight. So I guess it is age although it was just as old as the other two. However it was packaged much better.

Milliput comes in cello wrappers....Sculpt comes in plastic tubs that have simple lids...no seal of any kind. So I think that is the difference. All of these two part epoxy's say they feature long shelf life but none of them define how long "long" will be. Without some sort of effort to keep the air off the epoxy (Tamiya does make an effort unlike the other two) I would not expect "long shelf life".

[Paul R Miller]

Good to know you have a resolution to the problem at hand.