Thread: Two part expanding foam questions

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Hey, group. I have heard that some of you like to use the two part expanding foam instead of great stuff. I was wondering how difficult it is to use. Also, where can I get it and what is the price? I've heard this works better in molds because it doesn't have the shrinkage that greatstuff has. Any help would be great!
Thanks in advance!

Two part foam is cool but your mold has to be able to withstand the expansion. From my experience, once it gets going there is no stopping it. It made a couple of fat looking skulls. I’m heading to my shop soon, I’ll see what the price is on label.

My 2 quart was $35. Price is probably higher now. Maybe $40. It's not hard to use but I have few applications for hard foam.

Does the two part foam work better in latex molds, or should I consider using great stuff. I bought some molds that don't have a mother mold. I am trying to figure out the best way to get a good casting, without stretching the latex, so I can then make a mother mold to better support the latex for future castings. Any ideas? Other than not buying any more latex molds without a mother mold...

I have only used foam in RTV molds, never used latex. I imagine as long as you use the proper mold release you’re all good. Two part foam and Great Stuff will both stretch your mold without a mother mold. The two foams expand in all directions. Maybe, fill mold with hydrostone or another cheap plaster and then make a mother mold. I have never used Great Stuff for casting, only filling holes in my house.

In my opinion, there is no comparrison between great stuff and 2 part foams. Great stuff is not designed to be used for casting. It's expansion is always unpredictable. There are many different types of 2 part foam. Some are rigid and expand with force, and others don't warp in a latex mold even without a mother mold. It all goes by the foams density ratings. You can get it from Smooth On, or from cementex. I like Smooth on's better myself.

Originally Posted by Vlad

There are many different types of 2 part foam. Some are rigid and expand with force, and others don't warp in a latex mold even without a mother mold. It all goes by the foams density ratings. You can get it from Smooth On, or from cementex. I like Smooth on's better myself.

Vald, am I looking for a low density or a high density foam if I don't want the latex mod to warp? Sorry, it seems like a silly question but I'm "just a girl".

Hi MT !!, Here's the Smooth on page>>>>>>>>>>>
http://smoothon.com/foams.htm
I've been using the #5. It has enough of a cell structure to be a nice stable skull, but still fairly lightweight. Nice middle ground type stuff. I do find that you need to punch air escape holes in the latex mold in such points as the skull "cheek' bones. the foam doesn't even have enough force to push out air pockets otherwise. Here is a pic of my latex bucky skull mold. Please note the small holes are for air escape, and the large hole in the underside of the chin is where I pour in the mixed 2 part foam. Of course the rest of the cut seem is duct taped together before each pour, and I use liquid auto wax as a release agent. 2 part foam sticks to latex like you wouldn't believe. >>>
http://img.photobucket.com/albums/v1...g?t=1199769457
When Black Cat was buying some 2 part foam for me last time, she asked Cementex for an equivalent, and they sent back a 2 part rigid foam, which stretched apart the latex molds as it expanded, and left me with skulls as hard as bowling balls and just as heavy.

Vlad, have you ever tried spinning or vibrating your mold while casting to get the air out? Or, is that not recommended with this type of product?

When the expansion begins after mixing the 2 part foam, it's not really in a totally liquid state. It doesn't lend itself to "swishing" around the mold. It took a few trys to learn how much to mix each time, without overflowing or underfilling the mold during expansion. Then it's just a case of keeping the mold upright till it fills on it's own. The seam lines from the open backed mold, and the little bits of foam that extend out the air escape holes are easily trimmed off.