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Discussion Starter #1
So I know I should be using ultracal30 for my molds but I live in a small town and can't fimd it anywhere. Is there any chance that there is a way to mix something similar with more readily available ingredients? I've been using plaster of paris (I know, I know but I figured these first few are more practice and I have no plans on reproducing them more than once or twice).
 

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What Hump?
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Some people use hydrocal instead of ultracal. I doesn't hold detail as long (for as many pulls) as ultracal, but if you are casting latex out of the molds, the latex sets/dries a bit faster.

I actually sent an email to U.S. Gypsum when I was trying to find a local Ultracal supplier, and they sent me a list of distributors in Colorado; Reynolds Advanced Materials being one of them. It turns out, Reynolds rocks. They have EVERYTHING for molding and casting and their employees are all very knowledgeable and into Halloween type work.
 

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Discussion Starter #6
Wont plaster of paris work too ? Im sure its softer but with enough coats of clear laqure paint should toughen it up.
Yeah, that is what I've been using. I just worry about losing detail. The last mold I made I've run 5 times and it seems to be doing okay. To be honest my detail isn't anything fabulous right now anyway and once the molds wear / break I can sculpt a new version. I could use the practice any way. Thanks for the clear coat idea though. I always spray the side I pour the latex in but maybe I'll coat the outside too for extra support.
 

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Google the MSDS:

Plaster of Paris - 85%
Portland Cement - 10%
Crystalline Silica - 5%

By weight, not volume. Keep in mind that cement is nearly twice as dense as plaster. Silica is a carcinogen, so I doubt you'll find that at the hardware store. If I were to try reproducing it, I'd go 90 plaster to 10 cement, by weight. If you want to fudge it, go 94 plaster to 6 cement by volume, and you should be in the ballpark without overdoing the cement.
 

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Scared Silly
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If you're spraying clear coat on the mold that you're casting latex in, you're defeating the purpose of using plaster in the first place.

Plaster is used for casting latex because the porous nature of the plaster draws out the ammonia in the latex, creating a skin and allowing it to cure faster. If you seal that off, you're just making it harder for yourself. If you want to get more castings out of a plaster mold than the mold will hold up to, you save the first casting, fill it with soft polyfoam, and remold it when needed. That's your "master" casting.
 
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