Alginate Molds & Fiberglass Resin

[A Hunters Moon]

Okay, I've been trying to keep my thread count down by posting other questions I have in my previous posts. The only problem is that no one seems to see it the second time around. lol So here's another. Through a friend I can get some dental alginate for around seven a pound.

Do you think an alginate mold could stand up to having fiberglass resin cast in it?

I'm wondering if it would destroy the mold or if I could simply use a release agent of some kind.

 

[Emperor Chaos]

No, it will stick to the mold anyways and just get a big mess and a waste of money and time.
I tried that like 9 years ago before I knew about silicone rubber. Stone base molds (Alginate, plaster, ulrta cal) are only good for latex.

 

[A Hunters Moon]

I tried silicone for a different type of project way back but it took weeks to dry. Is there a particularly fast drying brand of silicone to buy? I'm assumning this is the hardware store type.

At the moment I want to sculpt and cast smaller parts for a plasma canon project I started some time ago. All of which I want to cast in fiberglass resin. Most threads I'm finding are bio related. Any tips, suggestions, or links would be appreciated.

 

[crawjaw]

If the parts are small, you don't want to use silicone and you need the replicas cast in fibreglass/resin then latex is ideal. Small parts can usually be cast in single sock type moulds and might not need any support case mould.
If you use alginate you could make a plaster replica and then sand/drill it to give you super sharp lines/detail, then re-mould as above.
Alginate is useless for direct resin casting.

Silicone from the DIY outlets can sometimes bring success but it would be much better to buy some RTV silicone from a recognized mouldmaking outlet.
Silicone moulds pick up more detail and can stand more wear and tear than latex usually. It is also less prone to shrinkage.

 

[Mannowar]

Apperantly, based on this thread, I've had much better luck with alginate than others here, but maybe it depends on what you're trying to acheive. As for detail, I use it for lifecasting and it will pick up every detail from fingerprints to pores to cuts on your hands. I've certainly never had any detail issues with it. I've cast both resin and plaster in them with no problems...
For lifecasting though, to me at least, I don't care if the mold is destroyed as long as I get the casting I'm looking for, so I just break it right off the new casting. If I'm lifecasting a hand for instance, with alginate, after molding, I'll hit it with a healthy dose of Ease-Release 800 and pour my resin or plaster. Once that's done, I remove the mold and pitch it.

But if you're trying to do multimple castings of cannon parts, you're going to want to go with RTV silicone. I use either Mold Max 30 or Dragon Skin, both by Smooth-on, depending on what I'm molding. If you were using RTV silicone that took weeks to cure, you must've mixed it wrong, as it will cure to handling overnight and fully cure within about 1 week. And by mixing wrong, I don't mean wrong proportions neccessarily, but you may not have thoroughly mixed the catalyst in, which will most definitely cause curing issues.

Hope that helps.

 

[A Hunters Moon]

The parts I'd like to mold are mostly flat or round objects with smooth edges. Nothing with a whole lot of detail. I'm not exactly sure what silicone I used last but RTV sounds like a good option. I may give it a go.