Ingredients to make plastic molds at home

Written by evelyn de matias
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Plastic moulds can be created in the home with the help of simple ingredients such as urethane RTV rubber, polyurethane casting resin, sulpho-plastics, mould release compound and resin filler powder.

Urethane RTV Rubber

Urethane RTV rubber is a two-component elastomer (elastic polymer) with exceptional resistance to tearing, elongation and abrasion. It is a good material for making plastic moulds. It has a rapid mould cycle because its simple mix ratios and low viscosities allow for easy moulding and processing. Elastic urethane rubbers are also used for stamp pads, concrete form liners, rubber moulds and parts.


Sulpho-plastics are specifically compliant for making plastic moulds and light castings. They provide tensile strength with clear outline. This sulphur compound is a stable material that acts as a bond to hold the filler together. The compound is highly flammable and not suited for ashtrays or any materials that handle fire and excessive heat. Once it is exposed to a minimum temperature of 112 degrees C, it will melt into liquid form. It is also used for manufacturing ornaments and novelty items.

Polyurethane Casting Resin

Polyurethane casting resin is a fast curing compound and is safer to use than polyesters. Its attributes include low viscosity, fast curing and a non-rising material that fabricates highly detailed shapes, replicas and moulds in minutes. The compound virtually does not shrink. Full cure of the resin takes between five and 10 minutes and produces a durable finish. This is also ideal for casting of small scale replicas and scenery.

Mold Release

A mould release compound is formulated specifically for mould casting and fabrication. It performs well with most liquid rubber and liquid plastic items. Using this material will release mould rubbers, such as polyurethanes and polysulfides, from master-prepared models. It can easily let loose different casting materials such as epoxies and liquid plastics from cured rubber moulds. It enhances moulding efficiencies for different casting applications and lengthens the lifespan of the master or production mould.

Resin Filler Powder

Resin filler powder complements the properties of a liquid plastic system before casting. This filler powder will improve the viscosity of the liquid resin system by serving as a thickening agent. Using filler powder with moulds affects strength, density, smoothness, machinability, sandability and colour. Fillers also reduce the occurrence of exotherm, a chemical reaction that releases heat while minimising plastic mould shrinkage.

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