Resin casting in cold weather
Resin prefers warm temperatures (not hot) and doesn’t like it wet. 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. Cured resin that feels oily is a common result of a curing area that’s too cold or too damp.
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.
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.)
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 full time. You can find a mini crock pot like this at kitchen stores or even use a potpourri warmer.
Several minutes before I am going to 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 warm 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.
For curing, I have a “hot box” to keep the air around the curing resin warmer than my room temperature for at least for the initial part of the cure time. You don’t really want the air hot just warmer than the cool room. The hot box does 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 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 in to the box, but I have seen hot boxes made with a card board. One of these days I am going to create something with doors so it’s easier to access the shelves without losing the warm air. While the heating pad and aluminum pan does does raise the air in the box a few degrees vs the room, I also keep looking for a small heater, something that would fit in the box without taking up much room, with more control over the heat level.
Before I start up my salsa pot spa, I turn on the heating pad to high with the plastic bin in place. This will start warming up the air that’s trapped under the bin and the air around the racks. Starting with the air in the room at a bit below 70F /20C, the heating pad arrangement can warm the air in the box to 76-78F / 22C which is much better for resin curing.
While I am waiting for my “hot box” to warm up and my resin to warm up in its bath, I get the rest of my supplies ready. I cover my work space with wax paper to protect it from spills and make clean up easier, I get out mixing cups and stir sticks, and put on my Nitrile gloves to protect my skin.
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 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 most cured resin is 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.
To measure the resin, I use two cups which makes it easier to see how much I am pouring. I also use drams because the numbers are the biggest and easiest to see. 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. Don’t add a lot extra or you’ll throw the ratio off.
You can 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.
When I have my resin poured, 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, carefully. 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 heat source, the heating pad. I replace the bin over everything.
Since the heating pad has an automatic shut-off, I turn it off so I can turn it back on again to high. The automatic shut off is timed, and I want it on high as long as possible. I will often come back after I know the heating pad would have shut off and turn it back on again for a bit longer on the warm, but it seems to do fine with having the warmest time at the beginning of the cure.
Without the warmth of the hot box, resin takes considerably longer to cure if the room is cold.
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 demold-able 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.
What are your challenges when resin casting in cold weather?