How to make and use a two-part silicone mould for resin casting

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They say a picture is worth a thousand words, in which case how much is a video worth? Well, we are about to find out as we have dug deep into the SylCreate archives to find one of the first videos we made, explaining how to make a two-part silicone mould and use it for resin casting.

Our casting resins, moulding rubbers and all the accessories needed are some of the most popular sellers on SylCreate. Model makers use them to produce highly detailed copies of masters or modified parts.

Artists like our friends at The Pea Hive create jewellery, trinkets, ornaments and other items. Industrial users use the casting and moulding process to bypass the need to fabricate new machine parts, instead opting to copy existing ones.

It is actually an industrial application being carried out in the video we found, as one of our technicians creates a copy of a gear using Polycast G26 Polyurethane Casting Resin and Sylmasta 380 Silicone Moulding Rubber.

The process though remains the same, whether it is a piece of a machine being cast, a necklace, a statue of a dog, or a scale Roman amphitheatre. Watch the video below and read on to discover how easy making a two-part silicone mould and using it for resin casting can be…



Step One: The Mould Box

Firstly, you need to make a mould box which, unsurprisingly, is a box in which you will form your silicone rubber mould. No exciting titles here, I am afraid – it does exactly what it says on the tin.

In our video, the mould box is formed using plasticard, Sylmasta CAE1500 High Viscosity Superglue and plasticine. The item which the mould is to be taken of is measured to create a box of the perfect size. Create a box too large and you are wasting moulding rubber; create a box too small and, well, you can probably see the problem.

There are lots of ways to create a mould box other than with plasticard. Essentially, anything which can hold the liquid moulding rubber in place until it sets will do. When we have run out of plasticard stock before, we have even been known to recommend that customers use Lego to make their moulding box…

The item to be moulded is then pressed into the plasticine, with impressions made in the plasticine which will act as keys for the finished two-part mould.

Step Two: Making the Silicone Rubber Mould

To make the silicone mould, the moulding rubber is mixed with the catalyst and stirred until the liquid is streak free. Once mixing has been completed, the moulding rubber is poured into the mould box to create the first component of the two-part mould.

Each grade of Sylmasta Silicone Moulding Rubber has a different de-mould time. Once the specified time has passed, the plasticine is removed to reveal the other half of the item which now needs to have a mould taken.

To prevent the two parts of the mould sticking together as the second half is formed, the rubber inside the mould box is coated with release agent. Next comes one of the most important stages of making a two-part mould and one that a lot of people forget, believe it or not.

To get casting resin into a two-part mould, the rubber needs a couple of holes through which the resin can be injected. As our video shows, these can be made by using plasticine to attach a couple of bits of plastic to the item being moulded.

The rubber will form around the bits of plastic, which can then be removed once moulding is completed to leave two holes in the finished mould. Without these holes, there is no obvious way to inject the resin into mould, which is obviously going to cause a bit of a problem down the line.

Once the plastic sticks have been attached, more of the rubber is mixed and poured into the box to create the second half of the mould. When this part has been left for the specified time, both parts are removed from the box and are now ready to use as a two-part mould.

Step Three: Resin Casting with the Silicone Mould

Moulds made using Sylmasta Silicone Rubber are reusable. Remember the Roman amphitheatre we mentioned a little earlier? All the arches for that were made from one mould, which shows just how durable and long-last a Sylmasta mould can be.

When it comes to using casting resin, Part A and Part B are mixed in the prescribed ratios and then injected into the mould through one of those very important holes that were created during the mould making stage. Enough resin is in the mould once it surfaces from the second hole, after which the mould gets a shake and a little more resin is injected.

After the recommended curing time has passed, the mould is opened up and sitting inside will be a highly accurate copy of the master made from resin.



As with most things in life, the more practice and experience that a person gains when resin casting and creating silicone moulds, the better their work becomes.

Most of our beginners kick off with the Sylmasta Casting Kit which contains enough G26 Resin and 380 Silicone Moulding Rubber to get started, alongside all the accessories needed.

The Sylmasta Casting Kit XL contains five times as much G26 Resin and twice as much 380 Silicone Moulding Rubber whilst individual resins and rubbers can also be purchased separately in larger quantities.

If you would like to share your casting and moulding creations made with our products, then please email photos of your work alongside the SylCreate materials used and a description to sales@sylmasta.com.

We love seeing them and would be particularly interested in seeing how any first-timers get on when following our newly-recovered instructional video. Happy mould making and happy casting!



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