i'm not familiar with hydrocal 30 we went though approx 7-8ltrs of mixed plaster for this bust and saved on more plaster around the shoulders by using plaster bandage. It would be best to pre-fill the mould with water and quickly tip this out and measure that volume of water. This will give you a rough idea of how much mixed product it will take to fill the mould.

Hi I'm not sure? we just researched the application and safety tips thoroughly then did it ourselves. first couple of attempts may not be perfect but with practice you can achieve this. we also had the help of a local artist who also had experience in life casting.