silicon molds

Has anyone done this? any reason why it would not work? How much heat do you think the silicon could take?

I believe the type of silicon in there casting kits can go up to around 500F.

Straight up silicon can go up to around 600F, but many mold casting silicons are slightly different. You can get the food safe silicon mold material and that is rated to 600ish i believe.

The amount it would take would depend on the size of what you're doing.

I’ve tried this during Christmas holidays and it is working pretty well. As it is said it smell awful but it’s working. Also, the curing time could be very long: 24 to 48 hours.

I’v also used Mold star silicone product for work and it’s a little bit more expensive but the mold are far better and more reusable…

For temperature, you’ll be find up to 250 degC or even more with the blue star product.


My molds are all made from smooth on's oomoo30 and have held up pretty well.

Dustin mentioned that he thought this might be related to your PET plastic slingshot project. If that is the case I would go for makin a plaster mold. It would be stabler and you would have no worries about heat.

So I use do molding and casting daily, part of my job.
Silicones are made differently, Oomoo for example is a tincure, cant handle as much heat, MoldStar is a platinum cure. Platinum can take more heat and lasts a whole hell of alot longer. (some are food safe also)

Then you have hardware store silicones, these have curing issues, are not food safe, do not handle well against heat etc. The hack isnt worth.
Check out for Spec sheets of many good silicone.

right now, my idea was to make a ‘rough blank’ shape, that could be molded, (and thus, reproduced) and that the ‘copy’ could be used to make a plaster form to press/cast the HDPE. I"m assuming that the plaster could break or be destroyed in the process, So I wanted to be able to reproduce the ‘original’ used to make the form multiple times.

I had originally thought about using the silicon mold, but realized it might not be stiff enough to tolerate the squeezing/pressing that I’m imagining could happen when ‘casting’ the HDPE,
so original (hand made blank -in clay or whatever) → silicone mold → secondary ‘positive’ shape → plaster or similar → press HDPE in plaster ‘mold’ → finish rough HDPE shape with woodworking tools…

I also want to try creating some patterns in the HDPE using the different colors of plastic that are available.