Multimould is a soft, highly elastic moulding compound. It has similar properties to silicone moulding compounds except that it is RE-USEABLE, hence the name "Multimould".
Multimould is a copolymer which melts at 160°C. It is non-toxic, but gives off fumes while molten which have a strong odour. It has excellent release properties and takes up very fine detail. No release agents are needed with Multimould. It has a high density (2,75) which helps penetration and levelling.
Multimould is ideal for making direct copies off metal, mineral or resin products. Its high elasticity allows moulding of large undercuts.
Castings may be made in Multimould with cement, plaster of paris, resins, ceramic, refractories, Hardcast, Versimould and polyurethane foam.
Preparation: Make a box to contain the model and the molten Multimould. Use solid materials as far as possible. Thermoplastics will fuse to molten Multimould. If wood is used dry it thoroughly. (Microwave drying is convenient) Melt the Multimould in a microwave oven until pourable. If bubbling and odour are noticeable, reduce heating rate. Multimould has a very low thermal conductivity and melting by any means other than microwave is extremely difficult. Pour the molten Multimould over the model in the box, covering the model but not filling the box. After cooling, fill the top of the box with plaster of paris. This prevents deformation in subsequent mouldings. Strip the mould and cast your product. When you have made all the pieces you require, the Multimould may be re-melted and used for the next mould.
Multimould is sold in slabs of about 850 grams at R216/Kg. This is about half the price of castable silicone compounds, which are not re-usable.
The standard colour is blue.
HINTS FOR WORKING MULTIMOULD
All materials in contact with Multimould must have a melting point higher than 140°C. Materials should preferably be solid, with no porosity. The problem with porous materials like wood, is that the air inside heats up when you pour Multimould over it, the air expands and comes out as bubbles. This can often be overcome by wrapping aluminium foil over the wood. Plaster of Paris dehydrates at high temperatures, and continues to give off water until the Multimould has set. It is best to preheat the Plaster of Paris for 24 hours before using it, to a temperature of 70°C. Low quality Plaster of Paris may crack when heated. Preheating the mould may be desirable if there are narrow cavities.
If your model is porous, preheat it to around 140°C before pouring. Thermoplastics like PVC and Polyethylene will fuse to molten Multimould. Good materials for moulding are metals, glass, and a polished granite slab or smooth glazed floor tile for the base. Remember that highly conductive materials like metal will chill and set the Multimould much faster than insulating materials.
Multimould has very low thermal conductivity, and is therefore difficult to heat up evenly.The answer is a microwave oven. Use a glass bowl and heat it for about 20 minutes. You will probably find that there is a solid skin against the glass and some bubbles in the centre. Stir it with a stick to get the temperature distribution even. Keep re-heating and stirring until it is a thick homogeneous fluid with no bubbles. Lift the bowl out with oven gloves and pour it, being careful not to get any on your fingers! If you overheat it, it will start decomposing and continue to react by itself. This is a disaster! Get it outside as fast as possible. It stinks and needle-like crystals will grow on anything in contact with the fumes. After you have finished with Multimould, heat the oven at maximum temperature on convection, to get rid of any residual smell.
If your mould is too large to heat a single batch in the microwave, you must either store some in a conventional oven while you melt the next batch, or you must cast in layers. If you cast in layers, you must re-melt the surface of the first layer before pouring the second layer. This is best done with a small blowlamp working off disposable camping gas bottles.
PREPARING THE MOULD:
Can you make it in one piece, or must you split it? Multimould will handle large under-cuts. To make the decision, feel the elasticity of the Multimould slab and use your own judgement. You can pour Mutimould onto set Multimould without fusing the two parts. To do so, make sure the set Multimould is cold. Sprinkle some talc onto the surface. A pouch made of a mealie meel bag distributes it well. If you have no talc, flour or other powder will usually do. When pouring, don't let all the Multimould impact on the same area of the set material. Make a box around your model. Usually the model is placed on the floor of the box, with the contact area forming the filling hole. Note that Multimould is very dense, and if your model is less dense, it will float in the molten Multimould. Multimould is very flexible, and normally the mould box is kept in place when using it as a mould.
To prevent distortion, make the mould box a little taller than required, and pour some Plaster of Paris over the set Multimould. The upper surface of the set Multimould is always slightly dished due to shrinkage, so if you place it on a flat surface it will distort.
Multimould gives perfect release from smooth solid surfaces. NO RELEASE AGENT should be used. Stripping can be improved from porous surfaces by application of a bit of soap. When casting into your mould, again, use no release agent, unless you are casting with epoxy or polyester (fibreglass). In some cases a release agent may be required. Use D.O.P., D.I.D.P. (Di-iso-decyl Pthalate) D.I.O.P.etc.
All casting materials are suitable. For good precision and finish at a fraction of the price of epoxy, Keramicalia can supply a dense white marble-like material called Keratab, high strength Sorel cements, called Keraset, quick-setting Versimould, low density Kerapump 3 and a variety of technical materials.
If at first you don't succeed, melt it down and cast again. That is the beauty of Multimould; your mistakes cost you only time.