Here’s a handy tip I recently verified experimentally with $60nz worth of fresh two part polyurethane ‘Supercast’ casting resin from TopMark: it freezes!
Yeah ok, I’m not recommending anybody actually freeze their casting resin, but chilling polyurethane resins is quite a common trick used to extend their working times. SuperCast is a fine product in itself that has many desirable working properties for me…bar one: it sets quite quickly, in around two minutes. This can be problematic, particularly if you’re pouring several detailed molds, then you’ve got to work fast.
It’s also a problem in summer when your garage is an oven and the working time of SuperCast goes down considerably. Hence I usually chill my resins in the household fridge (in a sealed plastic bag, on the top shelf), however then it’s a fairly long trek to fetch them. Our garage has a cabinet deep freeze so I thought: I’ll just pop the resin in there for 30 minutes before pouring this next batch of molds. Of course I promptly got distracted by some other project and left the bottles in overnight!
End result: Frozen polyurethane resin, or rather half frozen as Part B seemed to freeze while Part A remained a sluggish brown liquid. Fortunately resin has no water content (air moisture degrades it after all) so evidently freezing it has no ill effect, which I tested by promptly pouring a set of molds which set just fine.
Phew.
So could you freeze mixed resin for later use? Or would the moisture in the freezer still set it off?
Normal setting is an exothermic catalysed chemical reaction. Chilling the two parts simply seems to slow the onset of that reaction so freezing mixed resin wouldn’t gain you anything I don’t think.
People do freeze mixed epoxy putties because it does extend their working time. But with ‘green stuff’ and the like you’re talking a couple of hours of working time instead of a couple of minutes. So the reaction involved is a lot slower.
Exposure to air moisture (ie. when you open the bottles) degrades the resin parts involved (I don’t know the chemistry involved), reducing working times and eventually making the resin useless. Although that can take years in my experience.