Casting Powder - Plaster of Paris We sell three types of plaster; Fine Casting Plaster, Fine Casting Plus Plaster and Herculite 2 Hard Casting Plaster. Fine Casting Plaster and Fine Casting Plus Plaster are general use plasters with Fine Casting Plus Plaster having a better working consistency than normal Fine Casting Plaster. These plasters can be used for many applications, are easy to mix up and simple to use.Please Choose the Type and Amount you require above. How to Mix Fine Casting and Fine Casting Plus Plaster(1) First work out how much plaster you need and use this amount to determine how much water you will need to mix it with. The mix ratio for Fine Casting Plaster (any type) is 100/70, which means 100g plaster to 70ml water (for example if you need 500g of plaster you will need 350ml of water).