What is addition cure silicone & what is it used for? |  A Guide

There is a lot of confusion around addition cure silicone, mainly because there are different types and categories.

There is a lot of confusion around addition cure silicone, mainly because there are different types and categories to do with it. 

In this guide, we will answer all of the common questions about addition cure silicone rubber that we often hear about. 

What is additional cure silicone?

Addition cure silicone is another name for silicone that is catalysed or ‘cured’ with platinum. The word ‘addition’ refers to the curing system involved in this process that involves a mixture of a silicone polymer and a catalyst with the additional presence of platinum. 

What is condensation cure silicone?

Condensation cure silicone is another name for silicone that is catalysed or ‘cured’ with tin salts.

What are the main differences between additional cure and condensation cure silicone?

The main difference is chemical, referring mainly to the type of metal used to catalyse or cure the base rubber. In this case platinum is used for addition cure silicone and tin salt is used for condensation cure silicone. 

Both platinum (addition) cure silicone and tin salt (condensation) can be cured at room temperature. This similarity is often why they are often mixed up. But they are actually very different from each other, and they aren’t compatible with one another either.

No one chemistry type is superior over the other. Rather, each type has unique properties that give them the edge over the other type in certain situations. Here are the main differences between the two:

Addition (platinum) cureCondensation (tin salt) cure
Offer exceptional heat resistance and the ability to work under higher temperaturesConsiderably cheaper to make
Very pliable and toughBiodegradable 
Can split or tear if stretched or twisted too muchMore tear-resistant 
The curing process is trickier and requires more careful skill and accurate mixingTend to weaken after 1-2 years if they are overused 
Food safe, skin safe and transparent versions availablePreferred for general mould making — can capture very find & intricate details
Virtually no shrinkage in the cure processShrinks slightly during cure process
Incompatible to some chemicals including: nitrogen, sulphur, sulphur vulcanised rubbers, phosphorous and condensation cure rubbersWorks great with plaster casting, polyester, epoxy, gypsum, wax and resin

While we’re on the subject of differences, you might also be interested in our guide on understanding the difference between peroxide and platinum-cured silicone here. 

Properties of addition cure silicone.

Addition cure silicone is popular because it is very flexible yet durable, both water and fire resistant, and excellent for making moulds or casts. 

It is also remarkably versatile. For example, it can be combined with lots of different types of resins and materials. For example concrete, brick, fibre glass filled resin, polyester, stone, acrylic resin — and even another type of addition cure silicone.  

Other great properties of addition cure silicone mould making rubber include:

  • Available in many different shore hardnesses, making it suitable for  many applications
  • It can be heat-cured
  • Casting resin resistance
  • Compatible with silicone fluids to increase softness 
  • Low shrinkage rate of below 0.1%
  • High tear strength 
  • High tensile strength
  • Good resistance to abrasion 
  • Excellent dimensional stability means more durable moulds can be produced
  • Fine details are able to be reproduced
  • FDA approved food and medical grades are available 

Good to know:

Addition cure silicones do not produce by-products during the curing (cross-linking) process. All of the chemical reactions are contained internally. This makes them perfect for moulds or component parts that are manufactured in a sealed environment.

And because they are so durable and resistant to the elements (heat and humidity) they are ideal for moulds that often need to be stored away for long periods of time.

Applications of addition cure silicone.

Addition cure silicone is very popular across many industries. Including:

  • Prototyping 
  • Food (for example, food safe silicone mould rubbers)
  • Cosmetics 
  • Architectural replication & sculpting (for example, museums use platinum-cure silicone rubbers to make moulds of valuable works of art and artefacts)
  • Special effects
  • Prosthetics and orthotics 
  • Composites/fibre glass creation 
  • Dental replication 

Addition cure silicone is particularly good for resin and plaster casting. 

Performance differences.

Addition (platinum) cureCondensation (tin salt) cure
Inhibition Critically sensitive to sulphur and will fail to cure when exposed.May still cure over models containing sulphur if the model surface is sealed with an acrylic spray.
Shrinkage Generally stable and resistant to shrinkage. Exhibits higher shrinkage over time, though how extreme this is will be determined by many variables, including mould configuration, etc.
Library lifeA long library life, lasting even for decades. Library life can be as little as 12 months (which is fine if you have a short term project) or as long as 5 years — it depends on what type of tin-cure silicone you go with.

At the end of its library life, the mould will tear easily and be unusable. 
Production life Impossible to say — it depends on the application and a lot of other different variables. Impossible to say — it depends on the application and a lot of other different variables. 

Some chemical compounds can contaminate and inhibit the cure process, preventing the necessary cross-linking from taking place. 

Keep your addition cure silicone rubber away from the following materials: latex and rubber gloves, masking tape, amine, PVC stabilisers and epoxy resin catalysts. You also cannot let addition cure silicone come into contact with condensation cure (tin-catalysed) silicone, or any sulphur containing material either.

The types of additional cured silicone that we specialise in.

At Viking Extrusions, we specialise in addition cured silicone — or platinum-cured silicone profiles as we like to call them. 

We love working with platinum-cured silicone for all of the reasons described above, but also because it has excellent biocompatibility and is FDA and USP Class VI approved — making it suitable for medical and pharmaceutical applications. 

Over the last 30 years, Viking Extrusions are proud to have built a reputation based on exceptional customer service, fast lead times and the ability to extrude innovative and complex silicone products. We pride ourselves on our customer service, fast lead times, and ability to extrude complex probiles.

Interested in addition cure silicone rubber? Then we can help. 

We have been serving worldwide customers for over 30 years now with profiles and components that are both complex and diverse. We pride ourselves on the knowledge and expertise that is available in-house, accumulated through years of prototyping and development work.

Years of continued investment have resulted in the company owning an impressive range of plant and equipment that is both high tech and ultra-reliable. Now we have over 8000 stock dies for profiles, cords and tubes — ensuring that most requirements can be catered for without a tooling charge.

If you’re interested or just have a question about our services, contact us today. You can email us or telephone — we’re always happy to help. 

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