Why Does Resin Flash Cure? 3 Reasons It Happens

why does resin flash cureSo you googled ‘Why does resin flash cure?’ and ended up here. In my experience, that means one of two things:

You’re a resin nerd, and you love reading about everything resin. (Boy, are you in the right place 😜)


You mixed resin only to have it cure way too fast. With lots of bubbles. And maybe some smoke.

overheated resin with bubbles

But even when it does flash cure, it doesn’t have to be a total waste. (More on that in a minute.)

So I can’t explain this to you without having a mini chemistry lesson about what resin is.

Two-part resins produce heat when you mix the resin and hardener together. The heat causes the liquid to turn into a solid mass. And for you resin nerds, that’s called an exothermic reaction.

Pretty cool, eh?

But too much heat makes resin flash cure. And by flash cure, that’s where the resin cures much quicker than it should.

Every resin formula is different in how it produces heat. But regardless of the epoxy type, the more resin you mix, the more heat it makes. Too much heat causes it to flash cure.

As if making something full of resin bubbles wasn’t bad enough, resin that gets this hot might start a fire. The resin itself isn’t flammable, but the resin mixing cup might be. For safety reasons, it’s essential to know why your resin is too hot and flash cured. You want to know what to do differently next time.

So why does resin flash cure?

Reason 1: You mixed too much

One of the ways to control the heat is not to mix too much at once. That’s why your epoxy resin should say what the maximum mixing amount is for that resin. When you go above that amount, things go sideways, and you’re calling your resin a big ugly moose turd.

⭐️ BONUS: There’s more you should know about your epoxy, besides maximum mixing amount, before you use it. Here are the ten questions you should ask before you buy resin.

Reason 2: Your resin kit is too warm

warming bottles of epoxy resin in a hot water bath

One of the best ways to avoid resin bubbles is by warming your kit in a water bath before using it. It thins out the liquids, making it easier for bubbles to release. But, that doesn’t mean you need to warm up your resin to the temperature of the sun. The heat of the water bath adds to the heat of the resin reaction.

Reason 3: Something sped up the reaction

If a little is good, a lot must be better, right?

Nope. Nope. Nope.

Just like blowing up a dead whale with dynamite, adding extra hardener to resin is a BAD idea. Adding extra hardener (or anything else to speed up heat production) is another reason why resin can flash cure.

⭐️ BONUS:  If you’re in a hurry to finish your project, there are other ways to speed up resin curing.

What can you do to ensure your resin doesn’t flash cure?

resin mixing instructions

1. Follow the kit directions.
2. Don’t overheat your resin bottles.
3. Use your resin as soon as possible after mixing, so the heat doesn’t build upon itself in your resin mixing cup.

What do you do if you think your resin might flash cure?

You can cool down resin. (Believe me. It’s a thing.)

And if it’s too late and your project has already flash cured, don’t throw it away. I mean, you can if you want to, but you can turn your epoxy resin mistakes into something useful.

By the way, if you work with resin long enough, you’ll ask why does resin flash cure. Here’s what you need to know—it’s all a part of learning. Don’t be hard on yourself. I flash cure resin from time to time. If you don’t push yourself to fail, you won’t be an epoxy resin master.

Want to learn more of the resin basics with me?

It’s why I wrote the ebook, Resin Fundamentals. It’s the book I wish I had when I started with epoxy resin 15 years ago. I would have saved myself so much aggravation! Buy the PDF book now and get an email download link in minutes.

Unpublished Blog Posts of Resin Obsession, LLC © 2023 Resin Obsession, LLC

Like this post? You may be interested in  11 Best Resin Craft Safety Tips

9 thoughts on “Why Does Resin Flash Cure? 3 Reasons It Happens

  1. I have a two part sphere mold and no matter what resin I use it flash cures when I put the top on and finish filling it. Any ideas why this happens? I’m only pouring an ounce or two and pouring it right away.

  2. That was epic. Thank you for the video of blowing up a whale. I first heard about this a few years ago. I couldn’t believe it so of course Google here I come. But that is a perfect reference for mixing too much resin at one time! It sounds good in theory but no no no no. I was so shocked the first time I had a flash cure, all I could was stare at it!!
    Thank you for all the information you provide and the video. lol

    1. I did the same thing! Lol when it started smoking I was thinking this is not going to end well I picked it up to get it outside in the cold holy cow that was hot

  3. So, I have been using resin for 5 months now, and I never had a flash cure until today. I live in a climate that changes from cold to hot during this time of year. This is the first one I made since the weather got hot this week. I only mixed 4 ozs . I did out it in hot water to get the bubbles out which i started doing because its cold here in my house in the winter. Is it safe to say that during the hot months, I no longer need to put the cup in hot water even with my air conditioner on? This happened at 71 degree room temp.

  4. Today I got 2 flash cures in the same mold. I was making 13 different molds today, and the last 2 I used the same cup to pour into 2 different molds. One flash cured and the other didn’t. Afterwards I cleaned everything out and decided a new approach. I did an ounce each of different layer colors in this mold. None of them flash cured until the last ounce, however, I poured the other 2 Oz from the same mix cup into a different mold and it didn’t flash cure.. ???

  5. Tried to make a small box out of 6 indivifual sides, about 1/8″ deep. All pieces came out bendy. They are still bendy after 4 days of curing. Did i use too much color in my epoxi resin, or was it the fan, or the temp, or the temp of the resin?

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