Fine Casting Powder - Plaster of Paris Perfect casting powder for all types of crafting Easy mixing Perfect for figurine moulds High quality blend of plaster Can be painted. Picks up the fine details of the mould, body casting in conjunction with alginate, fridge magnets, tealights, sculptures, ceiling roses and many other creative projects. Fine Casting Plaster is a general use plaster and can be used for many applications, is easy to mix up and simple to use. Mixing instructions are detailed below. How to Mix (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 is 100/70, which means 100g plaster to 70ml water (for example if you need 500g of plaster you will need 350ml of water).