"Pink foam and RTV molds?" Topic

I was thinking of sculpting a few bits of wall out of pink foam, then making a mold off of them and casting the final pieces in resin.

Has anyone tried this? I figure that the foam master will die in the removal process, but any other problems?

Thinking about it, I will paint the foam masters with a thin layer of watered PVA to seal it before applying mold release and pouring the mold.

Also, this will be an open mold – the bottoms I want flat anyway, and not panning any serious undercuts, so making it in two parts isn't necessary.

Actually, I've never done a successful two-part mold. Whoops – rambling.

So, any thoughts from more experienced moldmakers would be appreciated.

the master may not get damaged at all as long as the rubber does not get into the pourus foam.
thin pva should do the trick, make sure you do all the master it should be fine

what are you moulding?

The RTV rubber will not attack the foam, but one normally uses a release agent on the master. And I suspect most of them would attack the foam. Urethane foam would be more resistant. But I think sealing any foam before trying to make an RTV mold makes the best sense. Gesso, PVA, Mod-Podge, would all work well.

If you want to try and capture all the pours in the foam, you will have to use the RTV without release agent. And it will bond very tightly. You would have to destroy the original to free the mold. As a worst case, you can dissolve the original with Acetone or other ketone or othere low polar solvent. (Big fire risk!)

DyeHard: Now that's an idea. Dissolve the foam back outwith some acetone… that would make the details crisper, don't you think – less damage to the mold than prying it out.

Shaun: I am thinking about doing some pieces to use as adjustable canals. Basically, the walls of the canal. The idea is that I just place some blue 'water' paper of whatever width I like between to parallel rows of canal wall.

I think it would work and make a very flexible system for vessels of varying beams.

I use Vaseline as a release agent. Doesn't affect the master or the mould. Brush on thinly.

Vaseline is a good release agent – instead of brushing it on directly dissolve it in mineral spirits and paint it on. The spirits evaporate leaving a thin coat of Vaseline.

The couple times that I did it, I applied a coat of acrylic paste (probably Golden brand, a couple of coats of Liquitex artist's acrylic matte medium to the foam, then sprayed it with gray enamel spray primer. The RTV was the old Dow-Corning HS-III. I had no problems de-molding the master once the rubber had set up. These were for one piece open pour molds of stone walls and Jersey barriers.

Thanks gents. I guess that is what I will try.