Talking of Moulding Silicones…

We always get asked – what is the difference between “Platinum Cure” and “Tin Cure” silicones used for mould making?

Tin silicone a.k.a. condensation cure silicones are usually foolproof and typically have a 100:2 to 100:5 mixing ratio by weight and once mixed, cure against most mould making media. It uses the condensation in the air and gives off alcohol as a by-product. Since there is evaporation in the form of the alcohol, there will be shrinkage of the same amount – approximately 0.2-0.5%. Tin cure is robust, high in tear strength and a great temporary tool. There are also thixotropic additives available which can be added in small percentages to allow for brush application. RTV Promould 30 is our version of Tin cure silicone with a mixing ratio of 100:3 and is available in White or Opaque.

Platinum silicone a.k.a. addition curing silicones are usually a 10:1 or 1:1 mixing ratio by weight and is a chemical reaction with no by-products. This implies that there is little or no shrinkage (less than 0.1%), making it a good choice for high precision parts. This silicone enjoys heat when curing, i.e. heating up will shorten the cure time. This silicone is preferred for high temperature applications and are highly durable when used with polyester, urethane, and epoxy resins but tests should be done when mould making is subject to surface inhibition caused by substrates like tin, Sulphur, oil clay, synthetic rubber, etc. We have RTV Silicone 5530 with a mixing ratio of 1:1 and is available in Green.

Contact us on 021 671 2114 or email for more info.