This article acts as a guide on all things ‘addition-cure silicone rubber’, including what it is, its applications, and the different types available. We have noticed there is a lot of confusion amongst our clients when it comes to deciding which addition-cure silicone is the best for their application and which solution will fulfil their needs the best.
In this guide, we answer all the common questions we hear about addition-cure silicone, talking through its properties, the different applications it can be used for, and much more. Read on for more information and to learn more about why Viking Extrusions is the go-to destination for all types of silicone rubber extrusions.
For more information on our addition-cure silicone capabilities or to discover how Viking Extrusions can help fulfil your rubber extrusion needs, contact us today.
What is addition-cure silicone rubber?
Addition-cure silicone rubber, also known as ‘platinum-cure silicone’, is a silicone that is catalysed or ‘cured’ with platinum to provide some of the most advantageous properties out of all mould rubbers. The word ‘addition’ refers to the curing system involved in the manufacturing process, which 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 rubber that is catalysed or ‘cured’ with tin salts, leading to more significant shrinkage of the part compared to the mould. One way condensation-cure silicone differs from addition-cure silicone rubber is its before-mentioned shrinkage characteristics, with addition-cure silicone delivering virtually no or minimal shrinkage.
What are the differences between addition-cure and condensation-cure silicone?
The main difference between the two materials is the chemical, mainly referring to the type of metal used to catalyse or ‘cure’ the base rubber. In this case, platinum is used for addition-cure silicone rubber and tin salt is used for condensation-cure silicone.
Both platinum (addition) cure and tin salt (condensation) cure silicone can be cured at room temperature, which is a similarity that often causes confusion between the two. However, they are very different from each other and aren’t compatible with one another either.
No one chemistry type is superior to the other. Rather, each type has unique properties and characteristics, giving them the edge over other types in certain situations, applications, and environments. Here are the main differences between the two:
| Addition (platinum) cure | Condensation (tin salt) cure |
| Offer exceptional heat resistance and the ability to work under higher temperatures | Considerably cheaper to make |
| Very pliable and tough | Biodegradable |
| Can split or tear if stretched or twisted too much | More tear-resistant |
| The curing process is trickier and requires more careful skill and accurate mixing | Tend to weaken after 1-2 years if they are overused |
| Food safe, skin safe and transparent versions available | Preferred for general mould making — can capture very find & intricate details |
| Virtually no shrinkage in the cure process | Shrinks slightly during cure process |
| Incompatible to some chemicals including: nitrogen, sulphur, sulphur vulcanised rubbers, phosphorous and condensation cure rubbers | Works great with plaster casting, polyester, epoxy, gypsum, wax and resin |
While we’re on the subject of differences, you may also be interested in our guide on understanding the difference between peroxide and platinum-cured silicone.
Properties of addition-cure silicone
Addition-cure silicone rubber is popular due to its very flexible yet durable properties, including being both water and fire-resistant and excellent for making moulds or casts. It is also remarkably versatile. For example, it can be combined with numerous different types of resins and materials, including concrete, brick, fibre glass-filled resin, polyester, stone, acrylic resin, and even other types of addition-cure silicone.
Other great properties of addition-cure silicone mould 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
- A 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 can be reproduced
- FDA-approved food and medical grades are available
Top Tip: Addition-cure silicones do not produce by-products during the curing (cross-linking) process. All chemical reactions are contained internally, making them perfect for moulds or component parts manufactured in a sealed environment.
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.
Applications of addition-cure silicone rubber
Addition-cure silicone is very popular in many industries, including:
- Prototyping
- Food (food-safe silicone mould rubbers)
- Cosmetics
- Architectural replication & sculpting (moulds of valuable works of art and artefacts)
- Special effects
- Prosthetics and orthotics
- Composites/fibreglass creation
- Dental replication
This type of material is particularly good for resin and plaster casting.
Performance differences
The table below represents the key differences between addition and condensation-cure silicone rubber:
| Addition (platinum) cure | Condensation (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 life | A 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. |
Warning: Some chemical compounds can contaminate and inhibit the curing process, preventing the necessary cross-linking from taking place.
Keep your addition-cure silicone rubber away from the following materials: latex and rubber gloves, amine, PVC stabilisers and epoxy resin catalysts. Also, you cannot let addition-cure silicone come into contact with condensation-cure silicone or any sulphur-containing materials.
The types of addition-cure silicone we specialise in
At Viking Extrusions, we specialise in all types of silicone rubber extrusions, covering multiple materials and moulds, including addition-cure/platinum-cure silicone profiles.
We love working with platinum-cured silicone for various reasons, including all the benefits mentioned in this guide, but also because it has excellent biocompatibility and its FDA and USP Class VI approval – making it suitable for medical and pharmaceutical applications.
Over the last 30 years, we are proud to have built a reputation based on our exceptional customer service, fast lead times, premium-quality products, and ability to extrude innovative and complex silicone products. We pride ourselves on the exceptional experience and customer service we provide to our customers as one of the leading silicone extrusion manufacturers in the UK.
How we can help
We have been serving a worldwide customer base for over 30 years, with profiles and components that are both complex and diverse. We have a wealth of knowledge and expertise due to the skills and experience of our in-house team, which has been 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. We now have over 9,000 stock dies for profiles, cords, and tubes – ensuring that most requirements can be catered for without a tooling charge.
If you’re interested in our services or have a question about our products, contact us today. Alternatively, you can download our free brochure online now for more information.
