The very best environment for working with epoxy resin is a steady 75° - 80°F and low humidity. But while we may get the occasional perfect day for resin casting, more often we have to deal with whatever our environment throws at us. This is especially true for artists and crafters who work outdoors, and even more so in the winter months. In this post I’ll talk about how temperature and weather affect epoxy resin projects. And more importantly, what you can do to keep working with resin on cold days.
How and Why Does the Cold Affect Epoxy Resin?
Epoxy resin works by mixing liquid resin and a hardener together to create a chemical reaction that hardens into a glass-like material. Like many chemical reactions, heat facilitates this process. In fact, resin doesn’t need to be exposed to air to cure, it just needs warmth. In addition, the reaction creates its own heat as well. Without enough heat, the chemical reaction is weakened or doesn’t happen at all. As a result, your resin casting will never properly cure. It may dry, but stay soft, bendy, and easily dented. Or worse, your project might remain gooey. How cold the resin itself and the room temperature are during and after mixing can determine how fully your resin project will cure. Cold resin may also appear cloudy even if it cures all the way because lots of tiny bubbles get trapped in the thick mixture.
Remember that when you’re thinking about temperature and epoxy resin, you need to think about three separate things: 1) The temperature of the resin and hardener before you start to mix them together, 2) The temperature of the environment or room you’re working in, and 3) The temperature of the area you leave your resin in to cure.
1) The Temperature of the Resin and the Hardener
The best temperature for mixing resin and hardener is 75°-80°F, but you can go up or down 5° and still get a good result. Keep in mind that if you mix resin on the low side of the temperature range, bubbles will have a tougher time escaping and you’ll need to put in more effort to eliminate them.
Resin gets thicker and more viscous at colder temperatures. By contrast, resin and hardener thin out as they warm up. Since you probably won’t be sticking a thermometer in your resin, use your eyes. Tip the resin bottle to the side and see how it moves. At the right temperature, resin and hardener are very liquidy, like warm honey, and move easily and smoothly.
2) The Temperature of your Environment or Room
If your mixed resin is nice and warm, and you have a warm place to let your project cure, you have a few degrees more flexibility with the actual room temperature while you work. This is especially the case if you're working quickly and the resin doesn’t have a lot of time to cool down. You can also use a slightly cooler (70°-74°F) environment to your advantage. After the resin is mixed, the slightly cooler temperature will give you a longer working time. This is really helpful if you are mixing up multiple colors, or have a lot to pour.
3) The Right Temperature for Curing Resin
Once you’ve poured your project you need to keep the temperature of the environment as stable as possible in order to keep the chemical reaction in the curing resin as stable as possible. Try to keep the temperature within 5°-10° for the whole curing time, preferably in a 75°-85°F range. Some fluctuation won’t affect the end result, but keeping it to a minimum is best. Also, don’t let the environment temperature drop below 70°F or you risk affecting the hardness of your finished project.
Cold Weather Tips & Fixes
So, does all this mean you should abandon epoxy resin in the winter? Definitely not! Once you know what to watch for and have a few tools at your disposal, you should be able to create with epoxy resin all year round. Read on!
How Do I Warm Up My Resin Before I Mix It?
This is one of the easiest things to fix. There are several simple ways to warm up resin and hardener. First, keep the bottles closed until they’re ready. If you have time to wait, just leave them in a warm area of your house or studio. A sunny window sill might be all you need. Or a kitchen counter. I often leave my resin bottles in the warmest part of my house first thing in the morning so they are ready for casting at the warmest time of day. If that’s not enough, or you need your resin warmed faster, put the bottles in a bucket or bowl of hot water. Don’t use boiling water. Just hot from the tap is fine. Depending on the volume of resin you are heating, you may need to change out the water to keep it hot. Remember to check the consistency of the resin to see if it’s warm enough. Wipe the bottles completely dry before opening them.
What If the Room is Too Cold While I’m Working?
As I mentioned earlier, the time when resin is most forgiving of the cold is while you’re working with it. Even so, you should keep the room temperature at at least 70°F. If you're indoors, turn up the heat shortly before you begin mixing. If this isn’t possible, close off a small section of the house or garage with a closed door, plastic sheeting, or fabric, and run a space heater. Bathrooms are perfect spaces to block off and work in, but you can also heat a walled canopy or shed for a short time with a space heater. If you’re in your house make sure to protect your surfaces; dried resin is permanent. Here you can see how I’ve laid a board over my bathroom vanity to keep it clean and give me a solid work surface. Also, if you’re enclosed in a small space with uncured resin, always wear a ventilator mask!
What If It’s Too Cold While the Resin is Curing?
Keeping an area warm for 8 hours or more is usually the hardest problem to solve in cold weather, so here is a list of ideas for keeping your project above 70°F while it’s curing.
You might already own something that can be used to cure resin, but be aware of a few important things. First, for any appliance, device, or set-up that doesn’t have a temperature calibration, make sure you have an oven safe thermometer and test the temperature before using it to cure your resin. Next, many appliance warming features only go as low as 150°F, which is too high for resin and resin molds. Check your device to make sure it can go down to at least 85°. Lastly, while many kitchen devices can be used for keeping your resin warm while it cures, you should never use the same appliances for resin and for food. Resin is usually safe for food once it’s cured, but not while it’s curing.
That being said, probably the cheapest and easiest solution for creating a warm spot in your house, shed or garage, is to use a heating pad (starting at $10), and put it either inside or around a box that will hold your project. If it’s very cold, the box will need to be insulated and the heating pad will need to be inside. You’ll need to do some experimenting and have a thermometer handy to check the temperature before you put your resin in the box. However, once you have figured out a configuration that keeps the box temperature at least 72°-75°F you’re good for the rest of the season.
- For small shallow resin projects like casting pendants, a food dehydrator offers perfect temperature control and low flat shelves. Food dehydrators start at $45.
- Electric warming lunch boxes, starting at about $35, are designed to keep your lunch warm all day and some can be used to cure resin. Make sure you check the lunchbox specifications for the temperature it warms at. Note that these lunch boxes may have small interiors, so plan accordingly.
- Insulated food carriers start at under $20. These are the silver-lined carriers you might get pizza delivered in, or that a caterer uses to bring warm food to an event. Some carriers are soft-sided and some of them are hard plastic. Some have electric warming features, otherwise you can put an electric heating pad inside. These can have a lot of room.
- Craft ovens and countertop toaster ovens will work fine if the minimum appliance temperature is lower than 100°. Most of them start at 150° which is not recommended for for more than about 10 minutes. Check the specifications and if you find one with a low temperature warming feature you’re good to go.
- Egg incubators start at $45. This is a pretty unusual suggestion, which I haven’t tried myself yet, but egg incubators can be set to keep a perfect warming temperature for a very long time. You’ll have to reconfigure the inside to lay your resin flat. And also check the height dimensions to make sure your project will fit.
- Kilns are an expensive way to cure resin, but the calibration is very accurate and kilns can be left running safely for hours or days. So if you happen to have access to a kiln, it’s a great solution for curing your resin projects.
- Turn up the heat. Literally, turn up the heat in the house, or the section of the house where your resin is curing. You can also close off a small area of your house or garage and run a space heater so that the room stays at least 72°-75°F. Make sure you know the safety
requirements for your heater and follow all manufacturer recommendations. Small space heaters start at $20 and are a good solution if you have a safe place to leave it running, where it can be monitored and be undisturbed by children and pets. Never put it inside of a box. A small space heater will do a good job of warming up a bathroom with the door shut.
Frequently Asked Questions
Should I have concerns about the resin cracking from the cold?
Unlike glass and ceramic, resin doesn’t crack from drastic temperature changes. If your resin is not fully cured, cold temperatures will keep it from curing properly. If your project is fully cured, the hardened resin will withstand boiling water or a trip to the freezer with no cracking or harm. It can even go straight from one extreme to the other without cracking as I show in these photos, where I pour boiling water on frozen resin.
Can the hardness of my resin project vary with temperature?
Yes and no. If the temperatures (as discussed) are warm enough for the resin to cure fully, the exact temperature won’t affect the resin’s hardness. The temperature will only affect how long the resin takes to fully harden. On the other hand, if the resin is too cold, then the lower the temperature the less cured the resin will be. A slightly too-cold temperature may result in a dry, but soft cure. But another 10° or 20° drop may leave you with a tacky mess. In both cases, once the resin has completed its chemical reaction, you can not harden it by adding heat. However, sometimes you can save a poorly cured project by adding new layers of properly cured resin over it.
Why does my cured resin have a wavy texture?
Another result of using resin that is too cold before mixing is that you may end up with a wavy surface, even if the resin hardens fully. This can happen if the resin crystallizes from exposure to low temperatures. If the distortions don’t interfere with your project, these waves are harmless and can be sanded flat. However, to avoid a wavy surface in the future, slowly and completely warm both the resin and hardener before measuring and mixing. This should get rid of the crystals and give you a proper cure.
Why Does My Epoxy Resin Feel Hot?
When you feel the outside of a mold and notice it’s getting hot, this is a good sign. It means the chemical reaction that hardens the resin is underway and your resin is curing correctly. Since this is a chemical process you may find that the curing resin is much warmer than the room it’s curing in. That’s perfectly normal.
What if My Resin Freezes?
The manufacturer says that IntoResin can get as low as 17°F and still give good results. This is great news if your resin delivery was left on a freezing porch, or forgotten in a cold shed. However, while your epoxy resin kit should be fine after a deep freeze, I wouldn’t freeze my resin on purpose, or purposely store it in freezing temperatures. Resin will have a longer shelf life and better predictability when stored at moderate temperatures; 60°-80°F. But if your resin does drop below freezing, don’t worry, with a little care you can still use it.
Frozen resin won’t become a solid, but it will get very thick. Never use it in this state. Before you pour or mix any resin or hardener, you must warm them both back up to at least 70°F, 75°would be even better. There are a number of ways to warm up frozen resin. If you have time to wait, just let it thaw in a warm area of your house or studio. The bottles will be closed, so they can safely sit on a kitchen counter in a warm spot. If you need to use your resin more quickly, put the bottles in a bucket or deep bowl of hot water. Don’t use boiling water. Just hot from the tap is fine. Depending on the volume of resin you are heating, you may need to change out the water to keep it hot.
What is the best temperature to store IntoResin epoxy resin?
The general rule of thumb is to store epoxy resin kits in an environment that stays in the 60°-90°F range when you’re between projects. It’s okay if the temperature fluctuates, or even temporarily goes above or below this range. My experience has been that if I store my resin inside the house at resin-friendly temperatures, I get more longevity and reliability out of my resin kits. When I store resin in the garage it usually still cures, but doesn’t last as long and sometimes yellows. Either way, always remember to warm your resin if it’s below 72°F before beginning a project.
IntoResin epoxy resin has a perfect consistency and excellent working and curing times at 77°, though I’ve had great results working five degrees higher or lower. A few degrees up or down won’t make much difference in the final product, but it does affect the timing of the process. The cooler your resin and environment are, the longer your working time (which can be an advantage) and the longer your curing time, which could be hours or days.
For example, IntoResin specifications quote the following parameters: At 77°F, with 55% relative humidity, you get 5-10 minutes of working time before your mixed resin starts to thicken. Your resin will set in 30-60 minutes and be fully cured in 8-12 hours. That’s the point at which you can remove your resin from a mold, drill it, or use your project. This is important to know so you can adjust your expectations with the weather, or adjust the resin and room temperature for a particular project. If you need more working time, you can keep everything a little cooler. If you’re in a rush, turn up the heat.
Give it a Try!
I live in Northern California. You would think that our long summer season and high temperatures would make it easy to find days that are perfect for working with epoxy resin. However, it really just goes to show that no place is perfect. Temperatures in the winter can go into the 30’s and it’s very common to have 40°F temperature variations over the course of a day. These huge fluctuations are not good for curing resin. Also, since we don’t get snow in the winter, we have poor insulation and seldom turn on the heat. Our indoor temperature is usually around 60°- 65°F degrees in the winter which is also not good for creating with resin. As a result, I’ve had to try many solutions to work in the cold weather, and have had many successes and my share of failures as well. I’ve learned to time my resin crafting with the warmest part of the day. I’ve learned which parts of my home warm up the best. And I’ve learned what month I have to bring my resin work indoors.
Hopefully, this article has helped you learn about cold weather epoxy resin crafting as well. Unlike when I began, you are now armed with information and a variety of solutions to try. Everybody has a different home/work situation, but there should be enough here for you to experiment and find what works for you to keep resin crafting year round!