How to cast plaster into latex Moulds
PREPARATION- FIRST STEPS
You have carefully read the instructions and have a clear idea of what you are about to do. You are going to fill a mould with a casting material and then support it so that it retains its correct shape while it sets. The three steps involved are:
(1) Mixing the casting material
(2) Filling the latex mould
(3) Supporting the mould while setting.
Take your time and get yourself properly prepared before hand and you will have no problems.
Mould making at certain times requires you to act quickly due to the rapid setting times of various products used, so it is a good idea to prepare carefully by having everything to hand before starting.
Give yourself plenty of room and cover all exposed surfaces with newspaper. You will need a bowl, preferably of a flexible plastic to do your mixing, access to water and soap.
For mixing you will need a flat bladed plastic or wood spatula or stirrer with a long handle. We use a kitchen plastic and rubber bowl cleaning spatula.
SUPPORTING LATEX MOULDS FOR CASTING
Next you need something to support the mould while the casting is setting. We prefer to use rigid cardboard boxes in which we can easily cut an opening for the mould to fit into. For production pouring, masonite could be used with the openings cut by jig saw to be more permanent.
To find the size hole to cut to support the mould while casting, moisten the mould base, turn the rim of the mould back and press the mould against a sheet of paper or cardboard. It will leave a damp impression of the mould base which will enable you to correctly cut a hole of the correct size into which the mould will sit supported by its collar.
For smaller moulds like chess pieces we simply a tall drinking tumbler or a jar of the right size. For large moulds we often turn to buckets of the right size anything to hold the mould steady and upright during casting.
We will deal with each casting material separately as each has its own particular requirements
With larger latex moulds that do not have a back-up mould to support the latex mould and thus yield a perfect casting, an alternative is to use the double casting method.
Double casting helps prevent the distortion that results from the unsupported latex mould stretching out of shape during casting and gives a professional casting.
* Make a support
* Fill the mould about one third full of water and pour into a mixing bowl. Add either the Moulding Powder or the StonePlast whichever you happen to be using until you have a creamy flowing mixture. It does not want to be a thin, watery mix.
* Rinse the mould out with water and shake dry. Pour in the mixture you have just prepared. Squeeze the mould to force the mixture to cover all the internal surface of the mould. Tilt the mould at different angles to allow the mixture to flow over the internal surfaces you have just coated with plaster mixture to keep building up the thickness. Continue until the mixture ceases to flow.
* Place the mould very carefully into the support so as not to damage the coating you have built up and allow to set up fully.
* Now fill up the mould fully with a freshly prepared batch of material being careful not to damage the existing hardened coating.
* When completely set remove the casting from the mould
FINAL CLEANING AND CARE
After completing your casting wash the mould before the plaster dries with soap and water, dry the mould and store in a cool, dry, dark spot out of sunlight.
If using flexible mixing bowls, it is easier to let the plaster dry and then by flexing the bowl it breaks easily away from the sides. DO NOT POUR YOUR EXCESS PLASTER DOWN THE SINK UNDER ANY CIRCUMSTANCES otherwise you will have a blocked drain. We keep a bucket half filled with water to rinse our bowls, spatulas while they are in use. The plaster settles to the bottom and can be disposed of by pouring off the excess water, letting the plaster at the bottom partially dry and then wrapping it in newspaper for disposal.
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