Can I cast a small concrete part in a plastic mold? Should I use a release agent?

Question

Ok, here's the thing, I am going to make a vacuum forming machine to make plastic molds. Can I fill the plastic mold that I make with concrete to make say, a small ornament? Will I need a release agent? If so, what kind of release agent?

Answer 1

I have made small ornaments out of Portland cement, using candy molds. No release agent needed. After it's fully dry it should release pretty well. After i take things from the mold, I wrap them in a wet towel for 3 days to make it even stronger.
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Answer 2

I have made molded objects using a standard bricklaying mortar. 4 parts sand to 1 part cement. They worked fine. Cement by itself can be brittle. If the mold is very smooth, you probably won't need a mold release agent. I'd experiment to find out. If I had to use a mold release agent, I'd start with silicone spray and also try stearic acid and talcum or french chalk powder.

Answer 3

I make molds of grogged plaster in plastic and always use a release agent. My favorite is Vaseline that i apply by hand and then wipe off to thin layer with a paper towel. I had something stick a tiny bit once and vowed never again.
Is a release mandatory? Probably not? Is it helpful? Yep!