I believe Fixall is the industrial version of Dental Plaster. Abyway I have used it for years and it cost about one fourth as much. I bought 25 lbs of Fixall for less than eight bucks a couple years ago.

Fixall will set even under water and in less than 30 minutes in cool air. I just made a fancy radial counter weight out of lead in a mold made from Fixall. Granted, I did not allow it to cure or bake it so two hours was not enough as it went a little wild when I pour molten lead into it. Things worked out fine but little minature volcanos erupted spitting micro missiles of hot lead. Whew! but it worked out nicely and the exposed surface could be mistaken for Lunar Art. I knew better but just wanted to see how far I could push it. Fixall when cured will give a perfect finish to lead castings. As a tool it can be put into use within two hours of casting but two days would be better.
-Rick