Pottery Plaster can be poured into moulds, used like Modroc when muslin is dipped into it, carved and applied to surfaces to create a textured finish. When it is mixed with water it will change from a pourable consistency into a hard solid when dry. During this change the plaster heats up. Various materials can be added to the plaster to modify its behaviour, e.g., salt to speed setting, wallpaper paste to slow setting. Aggregates can also be added to make the mixture occupy a greater volume, e.g., sawdust, sand, vermiculite.
To work out how much plaster you need:
1. Determine the volume of the mould you are using by pouring water from a mesuring jug, keeping track of the amount it takes.
2. Use the following formula to work out how much pottery plaster is required: volume in litres x 1.18 = amount of pottery plaster in kg (e.g., if the volume of a mould is 0.4 litres, you will need approximately 0.5kg of pottery plaster: 0.4 litres x 1.18 = 0.472 kg).
Please note that the weight refers to pottery plaster in dry powder form, not pouring form (i.e., before mixing with water).
This dry white powder must be stored in such a manner that water cannot come into contact with it.
Always wear a dust mask when handling dry powder. You may choose to wear gloves.