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Discussion Starter #1
I'm looking to cast some hands this year for a couple of projects and have never done any casting before. I came across Alja-Safe and was wondering if anyone here has used it before. I've seen plaster and latex used inside the mold but I'm curious if spray foam could also be used. Because it expands and the Alja-Safe is just a gel, I'm wondering if the foam would distort the casting and ruin it.
 

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It's a perfectly fine alginate to use. You may be able to find other brands for less. However, I don't think pray foam would work great on its own for hand castings.

A couple things to know about alginate: it's a temporary mold. You only get one good shot at pulling a casting from it. Why? The alginate is drying out from the moment it sets up. You mix the water with the powder to turn it into a molding material, but the water evaporates out fairly rapidly once it's set. Alginate is also very fragile, so it's unlikely, with something like a hand, that you'll get the cast part out of the mold without tearing it.

Now, spray foam isn't a great casting foam. Look at the other polyfoams that smooth-on has. You mix them and pour them into the mold as a liquid, and then they foam up. This lets them capture the detail, while spray foam will tend to leave big air bubbles.

I'm not sure that a polyfoam into alginate will work great, either. Something tells me that the moisture content of the alginate may interfere with the curing and expansion of the foam. I could be wrong, though.

If you want to cast into alginate, I would recommend a silicone skin backed with polyfoam. The silicone captures better detail than the foam would. You want a silicone that sets up very quickly. I've done this with Platsil Gel-10 (which cures in about ten minutes).

I don't think latex would work well in an alginate mold, since latex takes a while to cure, and you an either let the alginate shrink before the latex is cured, which could distort it before it's cured, or you keep it covered so it doesn't dry out, but then the latex might not cure. Not that it couldn't be done, but I think it would be a frustrating way to embark on your first molding and casting project.

The traditional way to do do latex filled with polyfoam would be out of a plaster mold, so you'd lifecast your model's hand in alginate, pour that up in melted clay, correct imperfections, then mold with a two part ultracal. From that, you can pour up latex, let dwell, then fill with soft expanding polyfoam.



BUT, as to your specific question, you'd not have a problem with expanding foam significantly distorting the alginate unless you way overfilled it and blocked the exit.
 

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Discussion Starter #3
Thanks for your advice, Mr. C. I knew that Alja-Safe is a quick drying substance and only one use. I don't mind that it dries quickly but it does suck that it's a one shot deal.

I agree that spray foam has air bubbles and voids and probably isn't the best to use. Imperfections don't matter too much for the project I'm working so I was really concerned about the expansion. Given the Alja-Safe is single use, I hesitate in trying it and wasting casting material if it doesn't work out.

I watched a few videos using this stuff and maybe they used silicone and not latex. The result was a floppy hand and arm which isn't what I'm looking for. I need something more rigid but not heavy. I bought a set of foam hands last season and was able to drill a hole up through it for a PVC pipe to mount it to my grounds keeper. That's the material I'm shooting for but just didn't know where to begin in getting the mold done.

I also saw CompsiMold, which can be reused BUT since you heat it to melt it, I didn't think sticking my hand in there would be a good thing to do! :)
 

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If you want a life cast you can use multiple times, use body double. I have gotten many clay pours out of life cast heads we did.

If you use alignate, it's best to use clay or a fast cure resin to get a positive. Them you can sculpt and modify that positive to your liking, and make a mold of it. Now you can make many copies of that prop.
 

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Discussion Starter #5
Thanks for the info Gadget. I'm still not sure what I'm going to do yet but at least now I have more product info to use in order to decide.
 
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