Moduling Silicone
Moulding silicone is a flexible and detailed material that is used to produce moulds or negative impressions. This allows precise copies or moulds to be made from a wide variety of materials. You are already familiar with silicone moulds from the food industry. However, typical areas of application also include mould making and reproduction in art, design and model making - for example when moulding sculptures, figures or spare parts.
A little silicone lore
Silicone is obtained from the versatile element silicon, which is abundant in the earth's crust and also forms glass and porcelain. Chemically, silicone consists of long chains of silicon and oxygen atoms. Two-component silicones are elastic, physiologically harmless elastomers that do not adhere to smooth surfaces and are temperature-resistant up to around 180 °C (220 °C for short periods). The moulding silicones from Modulor are easy to process, offer a high level of detail and cross-link at room temperature without additional heat.
How to mix 2-component silicones
When mixing, you must always adhere exactly to the mixing ratio of component A (polymer) and component B (crosslinker) by weight and (not by volume!). If you use more or less hardener than specified, you will cause vulcanisation problems and thus impair the subsequent mechanical values of the silicone rubber. It is therefore essential to use a precise scale to maintain the mixing ratio.
Which type of silicone for which project?
When it comes to silicones, a distinction is made between addition-curing silicones and condensation-curing silicones. We summarise the different characteristics of the two types for you - and which projects they are therefore suitable for.
Addition-curing silicones
- Vulcanise without releasing cleavage products
- Ideal for precise impressions that are to be used quickly after curing (wait approx. 24 h)
- Also suitable for larger projects such as hand impressions
- One component always contains a platinum catalyser
- Caution: even the smallest amounts of catalyst can trigger curing
- Contamination possible if A and B components are left open next to each other
- Close the container immediately after removal
- Clean tools thoroughly after contact with the component containing the catalyst or the mixture
Condensation-curing silicones
- Vulcanisation with release of decomposition products (e.g. alcohols)
- Shrinkage during curing by approx. 1 % due to evaporation
- Mould should be stored for approx. one week after curing until evaporation is complete
- Curing can be accelerated: store at 50-70 °C for several hours
- A certain level of humidity is important so that the condensate can evaporate
- Less susceptible to contamination → well suited for "unclean" environments, e.g. outdoors
- Processing at 20-50 °C; higher temperatures disrupt cross-linking (leads to non-curing or liquefaction)
- Always stir the A component well before mixing with the B component
Silicone moulds of the human body
Most of the silicones we offer are not actually designed for moulding the human body. However, such projects are particularly fun. On request, however, Modulor can also provide you with silicones that have been tested on the human body and are therefore proven to be safe. However, we recommend that you always carry out a small preliminary test before use (e.g. mould your little finger).
Storage and shelf life of silicone components
The individual silicone components do not have an unlimited shelf life. Details can be found on the manufacturer's packaging. The prerequisite for optimum shelf life and perfect end results is frost-free storage in the original packaging at temperatures below 30 °C. If you have removed partial quantities, you should not put any leftovers back into the original packaging. The finished silicone moulds also only have a limited shelf life. This means that they can only be moulded a certain number of times before they become brittle.
Liquid, uncured components are hazardous to water. They must not be allowed to enter the sewage system or soil.
Tools and aids you need for moulding
- A base (e.g. newspaper)
- Disposable latex gloves
- Cloth to wipe off any drops that have been spilt
- clean, dry measuring cups, disposable syringes and/or an accurate scale for precise measuring of the individual components
- Wooden stirring spatula, preferably a drill with stirring paddle
- Clean, dry mixing cups for mixing the silicone
- a stiff, short-haired bristle brush
- grease-dissolving cleaning agent (e.g. acetone or petrol)
Preparation of the master model
To produce a silicone mould, the master model to be moulded must be dry, clean, dust-free and stable. Moulding silicones have self-releasing properties - they do not stick to the master model when the mould is created and their castings do not stick to the hardened silicone mould when reproduced later. Nevertheless, we always recommend the use of release agents.
Porous materials such as wood, natural stone or plaster should always be sealed and coated with release agent before moulding. This prevents the impression material from penetrating the surfaces and making demoulding more difficult. An aqueous soap solution such as washing-up liquid or methyl cellulose (thin wallpaper paste) is suitable for sealing most materials. Alternatively, you can varnish these materials to seal their pores.
Here we go
Basically, the character and size of the master model determine the type of mould and the moulding technique. Experts differentiate between solid, skin and shell moulds. The consistency of the ready-to-use mixture is divided into pourable, spreadable and kneadable silicones, which are then - logically deduced - processed using the pouring, spreading or moulding technique. The different moulds and processes each have advantages and disadvantages. We have summarised these for you in a table below.
How to get your project in top form
- Stir both silicone components thoroughly before mixing.
- Pour the components into a clean mixing container in the specified mixing ratio by weight.
- Mix carefully. Observe the following tips:
- Include the container wall well when stirring.
- Mixing by hand (spatula) or with an electric stirrer is possible.
- The components are often coloured differently for mixing control.
- When mixing, incorporate as few air bubbles as possible, as they can impair the moulding accuracy and mechanical properties.
- When using a stirrer, mix at low speed to reduce air entrainment.
- After mixing, the silicone requires a deaeration time.
- After deaeration, pour the silicone rubber slowly into the moulding frame.
- Avoid air bubbles: first pour at the lowest point, then continue with a long, thin stream from a height of 20-30 cm.
- Vulcanisation begins at the end of the pot life: the components cross-link to form elastic silicone rubber. That's it!
How to demould your project
As soon as the silicone mould has cured tack-free, it can be demoulded. Use a scalpel to carefully cut one-piece solid moulds at a previously determined dividing line. It is best to use a transparent or translucent silicone for such moulds. This way, you can see the master model when you cut it open and won't damage it with your knife. Then carefully remove the silicone mould from the master model.
After demoulding is before casting
When you can start casting depends on the silicone used. Depending on whether you have worked with an addition-curing or condensation-curing silicone, the mould should then be stored for a day or a week before it is used for the first time. Suitable casting materials are plaster and plaster materials, plaster/acrylic casting resins, concrete, wax, unsaturated polyester casting resins, PUR casting resins or foams, epoxy casting resins, etc. To make your silicone mould last longer, you should rub it with silicone oil from time to time. You can also find an extensive selection of casting resins here at Modulor.
FAQs
TFC silicone is a two-component moulding silicone consisting of a base (component A) and hardener (component B). After mixing, it hardens into an elastic, tear-resistant and very detailed silicone.
As an alternative to silicone, you can also use elastic polyurethane or latex.
Only addition-cured silicone can be food-safe, as it is platinum-cured. However, not all platinum-cured silicones are food-safe. They may only be used for food if the manufacturer has expressly labelled them as food-safe (e.g. in accordance with FDA or EU regulations).
The temperature resistance of moulding silicone depends on the type of silicone in question. As a rule, it is around -50 °C to +200 °C. Heat-resistant special types are even more resistant and can withstand temperatures of up to +250 °C or more. Food-safe silicone, e.g. for baking moulds, is generally temperature-resistant up to +230 °C, in some cases even up to +250 °C.
Fast-curing silicone has a processing time of around 5 to 10 minutes and is fully cured after 20 to 60 minutes. With a pot life of 20 to 30 minutes , standard silicone offers a little more leeway and reaches its final hardness after 1 to 6 hours. Slow-curing silicone can be processed for up to 60 minutes and is only fully cured after 12 to 24 hours.
Moulding silicone is used to produce negative moulds. It is flexible, tear-resistant and very detailed. Casting silicone, on the other hand, is poured into an existing mould to produce a finished silicone object (positive mould). Depending on the application, it can be softer or firmer.