Making flexible moulds with silicone

Two-component systems, RTV, condensation or addition curing

Our silicones are two-component systems, i.e. you always need a silicone and a suitable crosslinker. Furthermore, they are RTV silicones, which means that the silicones cure at room temperature (Rroom-Ttemperature-Vcrosslinking). 

Basically, silicones are also differentiated according to the type of chemical reaction during cross-linking: there are condensation-cross-linking and addition-cross-linking silicones. Addition cross-linking does not produce any cleavage products, so that shrinkage is usually even lower with addition-cross-linking silicones than with condensation-cross-linking silicones. This is why they are particularly suitable for extremely detailed impressions (e.g. of human skin). For sculpture, however, even the condensation-curing silicones have a very low shrinkage. Please pay attention to the information given with the respective products!

For silicones with polyaddition crosslinking, it is also important to ensure that the quantity ratios are very precisely maintained and that the two components are weighed out very carefully accordingly. Even small deviations can interfere with the cross-linking and curing of these silicones. Polycondensation-curing silicones are somewhat easier to process.

Also be sure to check that the silicone compound and crosslinker are compatible. Polyaddition silicones and polycondensation silicones also cannot be mixed with each other!

Measure accurately: silicone, crosslinker, thixotropic agent

Since silicone is a two-component system, for impression silicone you basically need a cross-linking agent in addition to the liquid silicone compound itself, which ensures that the silicone becomes solid. Here, too, there are different variants: There are cross-linkers that make the silicone compound set faster or slower. When mixing carefully, pay close attention to the specified proportions. It is best to use a scale to measure exactly – otherwise you may find that the silicone does not set. This also applies to the two-component silicone putty, which has a different consistency from the outset.

If you do not want to pour the silicone, but rather trowel it, you can thicken it with thixotropic agent, known as thixo for short. This will make the mass more viscous. Again, pay attention to the exact quantities and mix carefully!

Pot life and demoulding time

Pot life refers to the time you have to process the silicone, i.e. from mixing to setting. Demoulding time, in turn, means the time it takes for the silicone to dry through so that you can remove the silicone mould from your master model. Pot life and demoulding time can vary greatly depending on the silicone compound and cross-linking agent, but also on the room conditions.

Humidity, room temperature, protective clothing when working with silicone

There are ideal conditions under which silicone can be processed best: these are around 23 °C room temperature and medium humidity. As a rule, the manufacturer's specifications for pot life and demoulding time refer to these ideal conditions. Strong deviations, e.g. high or very low humidity, high heat or cold affect the cross-linking ability of the silicone and can lead to the silicone not setting or – in the opposite case – having a greatly reduced pot life.

As some silicone components contain harmful substances, we recommend protective clothing with protective goggles, dust mask, gloves and apron.

Flexible moulds need support moulds

If you are building a multi-part mould from silicone, you will usually need support moulds, which are very easy to make from, for example, gypsum. Support moulds give the mould support and prevent it from collapsing, for example.