Do you need to have a porous mold to slush cast latex

Katsu Ma'roy

New Member

Short questions: Do you need to have a porous mold to slush cast Latex?

Longer narrative: I'm working on a complex piece. I've never made a mold before so I decided it would make more sense to mold the "flanges" separately, instead of attempting a 4 part mold.

The main part is being molded in Hydrocal, and then slush cast. I think I've got that figured out. The flanges have deep undercuts, and I was thinking that a silicone, or in this case, a "ComposiMold" (think thermoplastic, and/or remeltable) would work best. The flanges need to be hollow.

I live in an area with low humidity, as that may be a factor.


Master Member
No, I don't think you need a porous mold to slush latex. I would avoid using a silicone mold for latex though, as those two don't do well together. Plaster would do fine if you want to slush latex.

Mr Mold Maker

Master Member
Latex turns to rubber when the water and ammonia evaporate out of it. A porous material like gypsum wicks the moisture right out and makes it cure relatively quickly.

Latex when poured in gypsum cures against the stone and on the open area at the same time.

A non porous material can only cure from the open area, as the moisture in the latex against the mold has nowhere to go.

What you'll have to do with a non porous material is many many thin layers, allowing each layer to dry thoroughly before the next. It is very time consuming and annoying to build up any decent thickness. If you pour a bunch in too thick and a skin forms, it effectively seals off the latex inside and it will never cure.

Platinum silicone can be inhibited by latex while curing, but if the silicone has already cured latex will have no effect on it.

Does that all make sense?


Active Member
A "glove" mold probably won't work for the latex; unlike how silicone cures, latex dries (as described above by Slipknot), so it needs as much surface area as possible exposed to air. Plaster molds work nicely with latex because those materials also absorb the moisture out of the latex in addition to any of the latex exposed to open air.
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