Cleaning a plaster mold to pour silicone?

I have a old plaster mold that I need to pour silicone into and am having trouble with the silicone not setting due to a contamination of something. Can anybody tell me the best way and products to use to clean the plaster so the silicon will set nicely. Thanks.


  • If you are using a platinum-cure (or additive-cure) silicone, then contamination is pretty easy to cause.  Unfortunately, it is almost impossible to fix.  Tin-cure silicone is much more tolerant of contaminates, but there are still limits.  You could try some strong solvents like acetone, but my guess is you are going to be out of luck.  The biggest issue with plaster is due to its porosity.  It tends to draw in any and every contaminate deep into its structure.  Anything you clean off of the plaster will really only be at the surface and not get very deep.
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