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Permalink Reply by Dennis Heinzeroth on May 9, 2019 at 2:32pm

As I understand it, the porosity of the stone mould helps to bake off the excess moisture in the foam latex as it sets up into a "solid" piece. Sealing it would make that task more difficult and less effective.

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Permalink Reply by StopmoNick on May 9, 2019 at 6:59pm

Release agent comes with the foam latex kit.  But as an alternative, I use a soap solution.  

Shave some shavings from a bar of plain soap into a small container of hot water.  (Probably less than 1/8th of a bar, not much really.) As it cools it will become thicker, if it is too thick you may need to add some more water, you don't want it to set solid.  I brush that onto the plaster moulds (Ultracal and Hydrostone are the ones I can get here.)  I usually do a second coat.  it sinks into the plaster and doesn't leave  thick coating, but works as a release. I also use it for casting silicone in plaster moulds.   When the foam latex cast is cured and I take it out, I wash it in warm water, squeeze it, then leave it hanging to dry overnight.   That washes the soap residue off the surface.  I find it comes off more easily than the standard release agent in the kit, which avoids problems with the paint not sticking.

It does not seem to seal the plaster, so steam still evaporates through the plaster.

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Permalink Reply by tam hinton on May 10, 2019 at 1:59am

so release agent is basically soap? Maybe we are being 'soft-soaped' by the suppliers then, who charge a LOT for it, and it isn't always included in the kit.

thanks guys, i'll give it a go...

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Permalink Reply by Simon Tytherleigh on May 11, 2019 at 2:49pm

Yes, soap is the stuff!

It can also be used when casting silicone in a plaster mould.

When sculpting and creating the mould, I use a clay slip to ensure two plaster halves will separate. Vaseline does work, but will not go smooth, so if you get it on your sculpt, it can leave little lines.

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Permalink Reply by StopmoNick on May 11, 2019 at 7:23pm

The release agent you get with the foam kit contains Stearic Acid, so it is a sort of pearly white colour.  I did buy some stearic acid once and made some up, following a recipe, but soap works just as well.  

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