Epoxy resin overheated – resin is hot and smoking

resin is hot and smoking what happens when resin overheatsSomething happened to me recently mixing resin that hasn’t happened in a long time. While resin getting hot is completely normal (and should happen to make sure resin cures), my epoxy resin overheated and cured in its cup in about 90 seconds. Yes, it can happen to even the most experienced of resin crafters. I want to make this a teachable moment for everyone who creates with resin.

Let me set the stage:

After warming my resin kit, I mixed three ounces of Resin Obsession super resin to pour into three different molds. I poured the first two projects without any problems, but by the time I tried coloring the resin for the third project, it started to smoke. Within a minute, the resin heated significantly and fully cured.

So why did the resin smoke, get very hot and cure?

There are several reasons when combined, that caused my resin to heat up quickly and cure.

Factor #1

Resin kits have a minimum and maximum mixing amount. The minimum amount ensures enough heat is produced to start resin curing, but there can be too much of a good thing. Paying attention to the maximum mixing amount is essential to make sure the resin doesn’t heat up too quickly. In this case, I mixed three ounces of the Resin Obsession super clear resin, which is the maximum mixing amount for this resin.

Factor #2

While warming resin is excellent for reducing bubbles, that heat also adds to the heat of the reaction. While I usually warm my resin in a hot water bath for five minutes, I got distracted this time. My resin sat in hot water for closer to ten minutes before I used it.

Factor #3

I live in Florida. Even though it’s only March, it has been unseasonably warm for the last three weeks. The humidity hasn’t been bad, though, so my studio has the windows up and fresh air breezing through. Even though it was late afternoon, it was 80 degrees inside.

Factor #4

While I can’t explain in technical terms, when heat is produced in a cup of mixed resin and hardener, it builds upon itself. The more resin and hardener that is heating up, the quicker the heat builds. I only used about 1/2 ounce of the 3 ounces I mixed in my first two projects and let the other 2 1/2 ounces sit in the mixing cup, producing heat.

So what did I do wrong that my epoxy resin overheated — and what should I have done differently?

overheated resin in cup

1. Even though I made sure not to mix more than the maximum mixing amount, the extra heat from the resin sitting in the hot water bath too long added too much extra heat to the reaction. I should have paid closer attention to the amount of time the resin sat in the water instead of multitasking.

2. Because my room was warmer than what is ideal for resin curing (resin likes a temperature in the low 70’s F), I should have either turned on the air conditioner or waited until later in the day to pour resin after things cooled off inside.

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3. I should have used the resin for the ‘big’ project first. That way, there would have been less heat building up in the cup to cause it to overheat and cure.

So what should you know in case this happens to you?

Situations like this are why I always recommend having excellent ventilation when working with resin. In my case, I was working underneath a ventilation hood, plus had the benefit of airflow from the open windows. At a minimum, you should have air circulating to allow the fumes to move away from you in a case like this.’

Use cups that are designed to mix resin. Even though my cups got very hot, they didn’t leak, melt or crack. That always can’t be said for other paper or plastic cups. Worrying about the resin smoking is bad enough; you don’t want to worry too about the cup leaking resin everywhere.

Have a metal container handy when you are mixing resin. If your resin overheats and smokes, you do not want to put it into a plastic or cardboard container. These can also leak or worse — catch fire.

Do not throw the hot resin in your trash! The reaction is still occurring and can melt your trash can or start a fire. Instead, take it outside where it can sit on a surface while things cool off. In my case, I walked 10 feet through the front door and set my smoking hot resin on concrete to cool off.

Have a fire extinguisher close by.  While this is the worst-case scenario option,  it never hurts to be fully prepared should you find your epoxy resin overheated.

Want to see more about what happened?  Enjoy a close up of the bubble-filled, cured resin in this video:

Want to learn more of the resin basics so this and other mistakes don’t happen to you?  Be sure to grab your copy of the instantly downloadable PDF book, Resin Fundamentals.  The book gets you to resin expert status in only a couple of hours, even if you have never worked with resin before!

Unpublished Blog Posts of Resin Obsession, LLC © 2020 Resin Obsession, LLC

13 thoughts on “Epoxy resin overheated – resin is hot and smoking

  1. I’d like to know the guidelines on the amts that you can mix safely, as I know there is a big difference in casting, coating, doming resins. …and how much mixed resin does one need per sq. ft., please. Doming resins for coasters I mix no more than about 6 oz. (3 oz. ea.resin and hardener) for instance. Casting resins for a large cabachon…how much TOTAL should you mix safely…or a geode before dividing up into smaller cups for diff colors? Even a link to a chart would be helpful.

  2. I have a ruined carpet in my craft room from using a cheap plastic cup that melted and leaked when I wasn’t looking.
    Lesson #1 – Don’t use cheap plastic cups!
    Lesson #2 – If you have carpeted flooring, lay a plastic sheet down to protect it, like a painters tarp.
    Lesson #3 – Don’t leave your resin until it’s poured and covered!!

  3. Thank you for posting about this hardening issue in Florida! I spent all day prepping and waiting until midnight to try my 1st big pour last night… epic failure! I’ve been flabbergasted over how instantly the entire project went horribly wrong… and how I managed to mess it up so badly??!! Of all the projects I’ve taken on, the spectrum of materials I’ve used… epoxy resin is the first to kick my butt!
    After being upset over it for 12 hours now, you’ve made me feel better about things going wrong sometimes. .. but now what do I do?!
    It’s around 100 degrees, humid and gross… no avoiding this dilemma…
    Mixed great, had all my colors ready, randomly poured the 1st color, turned around to grab trowel and saw 2 melting cups that were half hardened already, other 2 cups about to do the same, so hot I really thought would catch fire! Grabbed bucket, water, got everything safe asap… of course the poured epoxy was basically cured in those 2 minutes also… wasted hours, materials and have a piece of my patio table out of commission, looking like a volcano puked on it in the garage….
    Eek!
    There’s no hope for a 70 degree day anytime soon. Its July, I’m in southern Florida… taking on the impossible!

  4. This just happened to me and I had never seen this before. I lost a lot of product and couldn’t figure it out and then I saw your hot water bath comment and had my ah ha moment. Thank you so much

  5. Katherine – Would a fire extinguisher be effective for a runaway resin / catalyst reaction? I have read in the past that the most effective method of dousing a uncontrolled reaction like that is to use sand to effectively smother the resin and allow the reaction to eventually cool. What’s your thoughts on that approach?

  6. So I am been doing resin shot glasses I’ve noticed that I’m getting a lot of bubbles in them. The fuel oil went out of the furnace yesterday but I did not realize it until after I had started pouring one ,poured in my silicone mold I put it in the oven on 210 for 10 minutes. Then I pulled them out to cure until today when I pulled them out it feels like shards of glass are running all up and down them. I’ve realized the oven is not the best way to keep up to get the bubbles out What else do you suggest?

  7. Reason 4, the fact that the hotter the resin gets the more heat that is produced, it’s pretty easy to explain in fact. The chemical reaction produces heat. The fastest the reaction, the more heat, and the rate of the reaction is dependant on the temperature,vso the hotter it gets he faster the temperature changes. In chemistry and physics these sorts of phenomena are common, where the rate that something changes is proportional to the total amount of that thing. In this case the rate that heat is produced, is proportional to the total amount of heat in the cup. The total amount of heat times a constant is the temperature in the cup. The solutions to such equations are exponential. Chemical reactions are known to runaway like that. Depending on the chemicals involved it can catch fire or even explode.

    In fact, items 1-3 are also related to this. The total heat as a function of time is an exponential curve. By starting with more heat, your starting further along the exponential curve, closer to the part where it runs away out of control.

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