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So long story short I've used Alumilite and another normal RTV silicone to make molds before in the past (both 2 part and 1 part molds). I have a resin (for counter tops), but it the exothermic reaction is pretty bad. It sets up fast too, like 2 min work time 10 min de-mold (thats why I like it).

I tried silicone caulk and cornstarch as a quick and dirty way to make a flying base for Xwing (before they sold them individually) and the Resin became super cloudy and fused the mold to the piece.

Side Notes: I dont own a pressure pot. I'm not trying to make 2 part molds. I'm making some rubble piles for the new Fallout game so 2in height and maybe 4 in long. I want them to have a flush to ground look, not mounted on anything. I'm not trying to get more than 2 casts out of these molds either so cheaper the better (if need be I could sell some casts on Ebay)

Would dish soap and silicone caulk method handle the exothermic temperatures?

Did I get the Silicone + cornstarch mix wrong?

Should I save my sanity and go for my normal RTV silicone?

Should I try plaster? I've never used it and I haven't done any research to know what to get.

Any good resins out there that are not to expensive that are good for casting without a pressure pot and have a mild to low exothermic reaction?

Thanks in advance!

Looks like we have used the same playbook!
Tried the cornstarch and silicone multiple times, was never able to get it to work right. The couple times I thought I did, the casts came out grainy once I demoulded.
Poked at the dishsoap method until I realized it was a long path to the same endpoint, silicone caulk just isnt't a great replacement for the real stuff.
Found a reusable option that I like. It has it's own issues but doesn't seem to fit the bill for your needs. If you decide you're going to need lots of small batch casts of different things hit me up and I'll give you a run-down on that.
Sounds like the biggest issue you have is the resin itself. The shorter that cook time, the hotter it'll cook. I really dig the Alumalite with 30 minute pour time. Think it says demould in 2 hours? I always leave it overnight, way better results.
Hobby lobby carries it and with the 40% off coupon they always have it's just over $20ish if I remember correctly.
It's not dirt cheap like some alternative work-arounds but still reasonable and actually works.
The starter kit they carry is also reasonable and effective. For casting a single sided mold, on a lower number of terrain casts I'd heartily reccomend.
Good luck and let us know how it goes!

^^ What they said.

The faster the cure time the hotter it gets from the exothermic reaction (it's a simple temperature/time graph, the shorter one axis is, the steeper the line will be).

For simple 1 piece moulds, you will usually always get a meniscus that forms (raised lip on the underside) because of the surface tension - this can be carved off before fully cured (when it's demoulded) or sanded flat when cured. I cast up rubble piles and walls from single sided moulds all the time.

I still have about a gallon of resin left... rather than buy more resin that cures slowly, I'll fork out more money and get RTV Silicone. Not cost effective but meh.

Ill sell some casts from the mold until the mold gives up.

I did buy some Oyumaru. Maybe Ill cast some barrels and tires in Plaster.

Whats the best bang for my buck for plaster casting? home depot plaster, woodland scenics, or another? Ill start researching but some first had insight would be great!

You can also refrigerate your resin (A+B before mixing) to give you a longer "work time". When it kicks off, it will still get hot, but because it has to warm up from "cold" (not room temp), it won't be AS severe.

We used to do this with "15 minute pot-life" resins in summer because they would start to go off in a bit over 5 minutes in the 40*C+ workshop.

I thought of doing that, and also keeping the mold cold also. Ill keep experimenting to see what works.

I think Ill make silicone caulk + dishsoap molds for the tires and barrels I have and cast them in plaster.

Ill fork out the money and get a Gallon of RTV. Ill have extra for another project down the line.

Thanks for your input!