Materials for casting

Size is a material used casting to slow down the setting time. It is in liquid form. The material is boiled in a bucket, left to cool down and then tested to see how long it stops the plaster from setting. All batches should be tested before application to make sure that the measurements used are correct in order for it all to have the same setting time. Grease/release agent is made a form of animal fat. It is mixed with cheap engine oil in a metal bucket. Once it has cooled, it can then be used to grease the moulds. If the weather is too hot, the grease will become very runny so this needs to be taken into account when applying to your moulds. Hessian or canvas is a reinforcing material that is used to strengthen plaster. It should be cut with a canvas knife or scissors. Laths are strips of rough timber and should be as straight as possible. Laths are used to reinforce and fix casts. Laths are a very dry material, so to stop them from sucking out the water from the plaster, they should be left to soak in water. Shellac is applied to plaster in 3 thin coats to seal the plaster and to stop it from soaking up water from any other coats of plaster that may applied.