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RTV2 Silicone Molding and Mouldmaking Rubber

Silicone Mould making rubbers have been in use as a mould making material for many years. These 2 part Silicone Rubber Materials have natural properties which make them ideally suited for use as a moulding medium for part reproduction as well as use for products in their own right.

General Features of Silicone Rubber

  • Fine detailed reproduction of most surfaces
  • Excellent self release properties (use of release agents not normally required)
  • Durable
  • Good tear strength and elongation
  • Low shrinkage
  • Easy and Simple to use

There are 2 different types of silicone rubbers:

  1. Addition cure systems which use platinum based catalyst.
  2. Condensation cure systems which use a tin based catalyst

Silicone Rubbers cured with either system have very similar properties but there are some differences which should be considered when using or making moulds from either type of Silicone Rubber.

Silicone rubber key differences:

Addition Cure Silicone (Platinum Based)
POLYMECH PROTO Series
Condensation Cure Silicone (Tin Based)
POLYMOULD Series
  • Low shrinkage, below 0.1%
  • Marginally higher tensile strength
  • Slightly tougher rubber
  • Need for careful and accurate mixing
  • Platinum catalyst can be chemically contaminated *
  • Good abrasion resistance
  • Can be accelerated using heat
  • Tolerant to the addition of silicone fluid as a softener
  • Lower costs
  • Wider range of properties available
  • Less sensitive to mix ratio errors
  • Easy to use with thixotropic agents to produce a brushable silicone rubber product.
  • Cannot be Heat Accelerated to speed up cure
  • Fast catalysts available to speed up cure
  • Mixing of grades possible to achieve desired hardness


For RTV2 Silicone mould manufacture such as prototype manufacture or the production where dimensions are critical and where shrinkage is not wanted, addition cure silicone rubber should be used. Condensation Cure RTV2 Silicone Rubbers are a popular, all purpose work horse type silicone rubber which will cure against most materials and provide the same level of detail reproduction as the addition cure rubber. Either type of RTV2 Silicone Rubber will self release from most masters or patterns with little effort **.

*Addition cure silicone RTV2 catalyst can be susceptible to attack from a range of different chemical compounds which will lead to an inhibition of cure which results in the silicone rubber not curing against some materials it comes into contact with, some of the  following chemical compounds should be avoided during the moulding and manufacturing process: nitrogen, sulphur, phosphorus, arsenic, organotin catalysts, PVC stabilizers, epoxy resin catalysts, sulphur vulcanized rubbers and condensation cure silicone rubbers.
**Certain materials need to be sealed prior to application of release agents and prior to casting any RTV2 Silicone Rubber against its surface, some of these materials are: plaster, timber, natural stone or any material that has an open grain or porous type structure to it where a mechanical lock can develop making release difficult.

Special Effects, Special FX, SFX and RTV2 Silicone Rubbers

Polymech RTV2 Silicone Rubbers have been used in the film, television and theatrical areas for many years and have been used to create props, special effects, animations and animatronics, prosthetics, stage and film set scenery manufacture. Condensation cure rubbers, such as Polymould 30, are used extensively to create plaster mock ups of interiors.

For example, a replica of a wooden panelled wall or plaster cornice can be reproduced using Polymould 30 Brushable series rubber moulding paste. Plaster is then poured into the mould and after set the plaster is finished to replicate the original items on a film set. A similar process may be used to re-manufacture things like, sculptures, natural rock, tree trunks and bark etc
RTV2 Silicone Moulding Material Application:
Silicone moulding rubbers find themselves used in applications for moulding a variety of materials, such as:

  • Wax Candles and used in the lost wax process for bronze casting
  • Polyurethane Mirror and picture frames, architectural mouldings
  • Plaster Covings and cornices, film studios, figurines
  • Polyester resin Giftware, figurines, sculptures
  • Spray on Silicone Rubbers for Vacuum Bag Manufacture in composite part manufacturing
  • Ceramics Earthenware pottery
  • Low melt alloys for fishing lures, toys, jewellery, models
  • Stone filled resins for the production of cold cast bronze works of art
  • Electronic Encapsulation for Electronic components and LED Lights.


Rapid Prototyping
Accurate prototypes are an important part of new product development. Once a master model has been created, further copies are made for testing and development. A fast and effective method of product development uses silicone moulds which are injected with a rapid set RIM resin.
Silicone rubbers that are commonly used for this application are normally translucent addition cure silicones, such as the Polymech PROTO 40.  Translucent silicone rubbers are used as it enables the master or model to be completely encased in silicone then using a knife, the silicone can be cut open to remove the master. The mould can be reassembled and resin injected to reproduce multiple copies of the original. Translucent RTV Silicones are preferred for these applications as it allows the rubber to be cut open to remove the master but also allows visual confirmation to see if the resin has been properly and completely filled the mould.
Prototypes are often used to prove and develop the fit of several components, and the use of a low shrinkage addition cure is essential.

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