Molds for ornamental plaster work

Does anyone here make molds to cast ornamental plasterwork?

I have mostly used latex which is brushed on in layers, but the molds tend to shrink quite a bit when they cure, and it distorts the casts. The liquid latex is pretty cheap though.

Has anyone tried any of the other molding materials? such as the silicone or urethane rubbers that are poured on rather than brushed?

All I can offer is that silicone is used a lot by artists. It holds up very well to repeated use.
You have to use a decent amount of silicone - don't scimp

I work with people who use silicone for casting. Work's a bit hit and miss at the moment but I can ask.
Presumably you've seen the videos of stuff like cornices being made by formers being slid along? And circles by similar but on a fixed radial arm?

Quite a. Bit of burlap is used as well

I have run plaster using the circle trick, but not in place on a ceiling, just to make a model for a mold. I am not sure I could run any amount of it on a ceiling. I have only done it by casting, and then gluing/screwing on to the walls or ceilings. I have mostly used the polystyrene cornices you can buy in the home centers as models, or pieces my wife has made from clay. Molds are filled with plaster of Paris, usually with some natural fiber string for reinforcing.

I am interested in hearing the experience of anyone who casts this type of plaster, and what they use to make the molds, or anyone who knows where people who do this kind of stuff exchange info on the internet.

The biggest problem I have with using latex, is that it shrinks a lot, maybe 10%, and so unless you are very careful when making the molds, the mold never sits in the mother-mold flat, and then the pieces are always a little distorted.

I believe most plaster was made on a bench, rather than in situ? Even if it was made on site it was made using benches rather than up a ladder? Gravity is hard to overcome.

I will ask a colleague who specialises in plaster work what she uses.