Thank you. I found several versions of the Hydrocal product at the USG site.In short, no. Look for a substance called Ultra-Cal or Hydro-Cal. It is similiar to Plaster, but will hold up to vacuum forming better.
Hmmm... I've had pretty good luck with water putty and Ultracal casts... but then I hardly ever make more than a few of anything.Actually, just about all gypsum products don't hold up well to vacuforming in the long run. The chipping will start shortly after a few pulls, depending on the shape of your mold. But if you're only wanting to make 3 or so pulls from it, then by all means, use it. If you're looking to make more pulls from a single mold, then I suggest using a heat resistant resin (like Smooth-Cast 385 from Smooth-On) or constructing the mold completely out of wood.
Alginate is water-based, and it shrinks and distorts as it dries, so it's only good for one-offs (or maybe two- or three-offs). You don't usually use it for making a bunch of parts, but for making a copy or two.I know there are cases of making silicone molds and then filling them with resin to make the additional parts. Will alginate handle this sort of thing? I'm assuming you just need the right release agent, but I'm completely new to this kind of thing...
Right, just make a negative mold in alginate, lay on a few layers of plaster bandage, then after the plaster sets, demold it, support in a sand box or something, and pour quick setting urethane into it. That's the theory, anyway.Ah. You think the best route might be using the alginate/plaster cloth for a quick pull and then just fill it with Kwik Kast for a nice master?
The alginate actually sets in about 8 minutes (a bit slower if you use very cold water---which you can if it's not a lifecast where you have to worry about goosebumps.) That's plenty of time to cover a human face, and enough for a whole head or a torso. (I think most people actually use the regular set for faces.) You spend more time making the mother mold than actually putting on the alginate.How large/complex of a surface can you lay up that way, since you said alginate sets in around 20 minutes?