Faults in Casting

There are a few faults that could occur when casting. Cockling is a fault that can happen in casting when using the two-gauge system. This happens on curved surfaces because of the length of the curve and the expansion. You can help to stop this problem by drawing a line through the first mix at certain points to make room for the expansion to happen. Casts sticking to the moulds is a fault that will mostly happen with reverse moulds. It happens because the mould is not greased properly and can also be because of poor sealing of the plaster which would then allow grease to be soaked into the plaster. Casts sticking to the moulds can also happen if shellac is brushed on when the plaster is too wet. Holes and misses will occur when using the two-gauge system if the first mix is not brushed in properly. Trapped air needs to be removed and this can be done by running your finger through the angles. Grease in the face of the casts will happen if you use too much grease. A piece of dry canvas should be used to wipe away the excess before casting. Cracks on the face of the cast, along the lath line occur when the laths are twisted. This can happen either when the laths have not been soaked appropriately or not putting ropes under the laths when casting. Loose laths during fixing can happen when the there has not been enough brushing in of the laths in the plaster, Strike-offs not being correct can happen when too much plaster is put on the canvas around the laths. The cast should not be hollow at the strike offs either, it should be built up with the plaster. If this is not done, the cast will crack or bow or both during fixing.