A mother mould is a special casing which supports a flexible latex, silicone or polyurethane rubber mould. It helps to prevent them distorting or collapsing when the casting material is poured in. These rigid supports can be made of any rigid material such as plaster, fibreglass or polyurethane plastics.The current material of choice for making mother moulds for larger subjects is fibreglass. The low cost and light weight of this material makes it ideal. Mother moulds for smaller objects tend to be made of plaster. If a latex mould is less than 200mm in height then you probably wouldn't need one at all. Moulds of this size can quite successfully be poured by suspending it in a hole cut in cardboard. On the other hand some China plastic injection mould Factory of around 100mm in size with a wide flat horizontal surface may distort and would definitely require a mother mould to support it.The rigidity of mother moulds is important so that it offers sufficient support to the flexible rubber mould. It is therefore important that the rubber mould has no undercuts as it can be difficult to remove from the rigid support when cast with material. The rubber mould can however have undercuts on the inside. The undercut on the external part of the mould can be filled with flexible sponge dipped in latex. Additional coats can then be added to make the outside of the mould smooth.It is also important to make the mother mould immediately after the rubber mould is made. The original object inside the rubber mould will hold the rubber mould to its true shape and the mother mould will support the mould accurately.Making a Plaster Mother Mould for a Latex Mould.As soon as the latex mould is complete and dry apply a fine coat of petroleum jelly on all exterior surfaces of the mould. This will aid in the removal of the mother mould when complete.Most mother moulds need to be a two piece casing which needs to be fastened together around the latex mould. You will need to find the easiest parting line for the two pieces to separate from the mould. This is usually on the less detailed areas of the mould. Once you have decided where your parting line should be mark it out with a pen on the latex mould.
