Posted by joew on January 23, 19100 at 10:08:04:
In Reply to: seperator for cement casting posted by JLTaylor on January 21, 19100 at 02:17:55:
Any unbroken soap film will prevent things from sticking to smooth plaster surfaces under normal conditions and temperatures, including portland cement and plaster itself. If the surface is really rough, you might have to take special steps, as in the recipe you mentioned.
Commercial mold soaps are liquid, non-detergent soaps. Potters use lots of plaster molds for slip casting. Try a ceramic supplier for mold soap. ($15 / gal.)
I prefer 'Tincture of Green Soap' for small molds. Doctors use it to cleanse wounds. Its 65% alcohol so it dries very quickly, like in 10 minutes. It works fine on cement-plaster. One or two carefully applied coats has excellent release and holds up for several castings.
Get it at a pharmacy or drug store in a 4 ounce bottle. It might be available in gallons.
Or get a box of Ivory Snow. Boil some water and dissolve some soap flakes in it. The water is absorbed by the plaster, leaving a layer of soap. Use too much soap and you have to scrape little congealed balls of soap off of the mold. Have fun experimenting, but starting with a liquid soap is better than making your own.
Another thing to try might be automotive hand cleaner. Go-Jo and Goop are popular brands. Automotive parts store. This one here contains lanolin (a fat) petroleum distillates (could be kerosene or some solvent for the fat) and a fatty acid soap.
Chances are there are many things that will work. Lots of the old recipes from earlier times are now on the shelf in the supermarket.