Resin casting in cold weather
Resin prefers warm temperatures (not hot) and doesn’t like excess moisture. Resin that’s too cold is like molasses. While you’re attempting to mix the parts, no matter how slowly you stir, you’ll trap all sorts of bubbles. The thicker consistency also makes it tough to fully combine the two parts. Since part of the curing process is a chemical reaction causing heat, resin that’s too cold can have problems curing properly. Sometimes resin that cures soft and bendy cured at too cold a temperature.
I live in British Columbia, Canada where it is cool and rainy most of the year. I also like it cool and rainy, well, not rainy inside, so I am living in the right place for me. So for most of the year, I have to plan ahead to have successful pours.
Tip 1: Turn up your room temperature
I’m able to set the heat for a single room, so I’ll set the thermostat up a bit for my workshop and keep the door closed to trap that warm and keep out the cool. Turning the heat up in that room also helps to dry it out a bit, too. (Yes, this really is how cold it is before the heat gets going.)
Tip 2: Warm up your resin kit
To warm up the resin, I give it a “spa day”, a warm water bath for 10 minutes. I have a salsa pot mini slow cooker which keeps the water warm during the spa time. A bowl of warm water will work, but the water doesn’t stay warm the entire time. You can find a mini crockpot like this at kitchen stores or even use a potpourri warmer.
Several minutes before I start mixing, I fill the salsa pot with warm water and turn it on. I use the salsa pot to keep the water warm while ‘bathing’ the resin, not to heat the water. It takes longer to heat the water from cold and I am a lot more likely to overshoot the warmth I want.
When I’m about 10 minutes away from when I want to mix, I put the resin bottles into plastic bags (without holes) and then into the pot. I can put the bottles directly into the pot, but it’s messier (and destroys any paper labeling). If I am going to be using liquid colourants, I also put them into the pot with the resin.
While I wait, I also prepare any molds I plan to use. For this example, I am using an Ice and Treat mold to make some Halloween items. I bought this one on sale a couple of days before Halloween. Wa-Hoo!
WARNING: If you use “food” mold for resin, do not use it for food after. Once you use it for resin, you should think of it only as a resin mold. While cured resin is likely non-toxic, you still don’t want to ingest it. Also, many of the inclusions for resin might not be good for you either.
After the resin has warmed up, I take the resin out of the spa and make sure the bottles are dry on the outside. You don’t want to accidentally drip water into your resin mixing. I unplug the salsa pot because it doesn’t have an auto-shutoff.
Because I’m working with small volumes of resin in molds, I’m using the Resin Obsession super clear resin. If you aren’t sure which resin you should be using for your project, be sure to check out our article on how to choose a resin.
To measure the resin, I use two cups which makes it easier to see how much I am pouring. I’m using Resin Obsession Super Clear which is a 2:1 ratio two-part resin. In this example, I poured 2 drams of part A and 1 dram of part B. I could have poured 4 and 2 or 6 and 3 or, well you get the idea. When the weather is cold, I add 2-3 extra drops of part B, which is the hardener. This helps to offset the cold a bit. While you might think adding extra hardener is a good idea to help heat up the resin, don’t! Here’s what happens when your resin overheats.
Tip 3: Create a resin hot box
Resin casting in cold weather also means I have a “hot box” to keep the air around the curing resin warmer than my room temperature for (at least) the initial part of the cure time. Simply having the air in the box warmer than the room air will help a lot with curing. The hot box also does the double duty of protecting the curing resin from unwanted inclusions like dust, cat hair, human hair, or anything else that might wander by and drop in.
My ‘hot box’ is put together from a pair of super-cheap letter trays sitting on an inverted low profile aluminum pan, sitting on an electric heating pad (that has an automatic shut off), and covered with an inverted clear plastic storage box. I like the clear bin so I can see into the box, but I have seen hot boxes made with cardboard.
Tip 4: Warm up your resin mold
When you are resin casting in cold weather, warm up the mold before pouring the resin by using a heat tool, just don’t get them too hot. When using plastic molds, if you heat them up too much, they can warp and distort. So, just enough heat so the mold is not cold.
After pouring the resin, using the heat tool not only helps to pop bubbles that might form, in cool weather it also helps to warm the resin and start the curing process. In the time it takes to mix and pour, in a cool room, the resin will have cooled down again.
After pouring the resin, I carefully remove the plastic bin, without tipping it (to keep the trapped air trapped) and set it aside. I put the freshly poured mold on the rack. If I am only inserting one mold, I put it on the bottom shelf which is the warmest in my “hot box” because it’s the closest to the heating pad. Then, I replace the bin over everything.
Since the heating pad has an automatic shut-off, I check it several times during curing to make sure it’s still generating heat and hasn’t turned off.
Enjoy your cured resin charms!
When the resin is cured, take it out of the hot box and do the normal stuff to finish it.
Super Clear cures to a demoldable stage in about 6 hours. This quicker cure time for an epoxy resin makes it great for a single-day project. If you take it out of the mold at 6 hours, when you first take it out of the mold, it will still be a little pliable but completely non-sticky. You can sand and paint or do other finishing effects immediately. The resin will continue to harden and should be fully hard after another 6-12 hours.
When I demolded the items, the beaker was too thin right by the top. I didn’t want the item to get too bulky and the bottle part was more recessed so I didn’t pour in enough to that cavity. First time using a mold, you discover things like that. Next time I’ll be able to gauge the depth for that cavity better. Everything else turned out great.
I added a bit of paint and some bails to the skulls and eye to make pendants. I glued the eyes back to back with the bail between them to make a 2-sided pendant. I’m not sure what to do with the worms other than just to leave them on the counter as decoration.
I made a decorative tag with the vials and beaker. I added a bit of paint to the vials.
Having more challenges beyond resin casting in cold weather?
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