Epoxy properties

[mlehikoinen]

Looking for some information or experience of others with Epoxy. Having a little difficulty finding what I need through google (gasp!).

How does epoxy react as it ages? Does it yellow like plexi-glass? Does it become brittle?

What doesn't stick to epoxy? I'm thinking of making some epoxy castings for a project I'm designing and wondering what I would like the form with to prevent the epoxy from sticking to the form.

Any thoughts or insights would be appreciated!

[PaulMarcel]

Based on West System product literature, it can be affected by UV, which makes it more brittle. Otherwise it doesn't change much over time. Hardeners will impart a slight yellow hue to the epoxy, but if you are coloring it, you're fine. In the case of West System epoxy, there are numerous fillers you can get from high-strength to easily sanded and faired. All the fillers will make the epoxy look cloudy. For black epoxy, graphite powder is the best vs a dye (plus graphite is light fast).

"High-energy plastic" doesn't stick to epoxy, which is why the epoxy pail, spreader, and stir stick are made of the stuff. Think of the plastic used for CD cake boxes. Nothing sticks to it. If you are making a mold, you could remove it once the epoxy starts to set. Epoxy is an exothermic cure so it generates heat. When you spread it thin, the heat is no issue and in fact because it is thin, it will cure more slowly. Left "in the pot", a mass of epoxy will generate impressive heat when it gets close to fully catalyzing and once it gets there, its very quick! My last project left maybe 3 tablespoons in a "high-energy plastic" container while I went about clamping, fussing, cussing on a project. I then noticed a whisp of white smoke... it was coming from the "mass" of remaining epoxy in the container. It was too hot to handle, smoking, melting the plastic, and rock hard. The rest of the epoxy that was on the project spread in dados was still quite liquid. A concentration of the stuff only makes the catalyst more effective.

Oh, I kept quoting "high-energy plastic" because I don't have a decent way to explain it. That's what the stuff is called, but what the chemical attributes are of the plastic is beyond me. Generally they are non-stick plastics.

I'm not sure what you could do for a release agent in the mold. Wax might work.

Lastly, if I were trying to make something structural, I might consider Bondo first. Definitely can release it with wax, much cheaper, doesn't set quite so quickly, easily faired. It is a bulk version of epoxy whereas stuff like West System or System Three epoxies are very fluid liquids you have to thicken and you'll never get the volume of Bondo out of the can. If you want the nice smooth surface epoxy can give you, shape it with Bondo, smooth it out nicely, then dunk the part in colored epoxy.

Would be cool to see what you come up with!

[mlehikoinen]

Thanks PM, as always, you're simply a mine of information! When my idea comes from concept to fruition, I'll be sure to share!