What Ingredients Do You Need To Make Silicone Molds?
Silicone molds are a versatile tool used for creating detailed castings and replicas out of various materials like resin, plastic, metal, wax, soap, chocolate, and more. Silicone rubber is valued for its heat resistance, flexibility, and ability to capture extremely fine details.
Some of the benefits of silicone molds include the following:
- Flexibility – Silicone’s flexibility makes it easy to de-mold castings without damage. Silicone molds are pliable and can bend to release parts.
- Reusable – Silicone molds can be used repeatedly to create multiple castings with a long service life.
- Non-Stick – Silicone naturally repels adhesion from many materials, allowing for easy release of castings.
- Heat Resistant – Silicone maintains its properties at temperatures from -45°C up to 200°C making it suitable for casting materials like wax or chocolate.
- Detail Capture – Silicone flows smoothly over surfaces to capture extremely fine details and textures of objects.
With these properties, silicone molds are ideal for rapid prototyping, limited-run manufacturing, hobby casting, and confectionery making. They allow for replicating complex 3D geometries in a reusable mold.[1]
Types of Silicone
Two main types of silicone used for mold making are liquid platinum cure silicone and liquid tin cure silicone (Complete Guide To Silicone Molds,2022). Platinum cure silicone is more tear resistant and durable than tin cure, but also more expensive. Tin cure silicone is cheaper but can eventually tear down over repeated castings (Silicone for Mold Making, Temu).
Platinum cure silicone is the preferred choice for making high quality, long lasting molds. It has a longer working time, cures faster, and results in a more heat resistant, flexible, and tear resistant mold. The main advantage of tin cure silicone is the lower price point. For one-off molds, tin cure silicone may be suitable, but for production runs, platinum cure is recommended.
Selecting Silicone
When selecting silicone for mold making, you’ll need to consider the type of silicone, food safety, viscosity, and mold release agents.
The two main types of silicone used for molds are tin-cure and platinum-cure. Tin-cure silicone is less expensive but can inhibit platinum-cure silicone from curing properly. Platinum-cure silicone is more expensive but has better tear strength and heat resistance. It’s also safer for casting food items (source).
For food molds, platinum-cure silicone labeled “food safe” should be used. Make sure the silicone does not contain phthalates or latex (source).
The viscosity of the silicone determines how well it picks up detail. Low viscosity silicones around 500-3500 cPs are good for detailed molds. Higher viscosities around 5000-20,000 cPs are good for larger molds (source).
Using a mold release agent can make demolding easier and prevent mold damage. Common mold release agents include petroleum jelly, liquid soap, PVA film, and commercial release agents (source).
Basic Equipment Needed
When making silicone molds, you’ll need some basic equipment and tools. Here are the key items you’ll need to get started:
Containers
You’ll need containers to mix and pour the silicone into. Plastic cups, buckets, or bowls work well. Avoid using containers made of silicone or latex, as the silicone may not cure properly. The containers should be clean and dry.
Mixing Tools
Use wooden sticks or plastic spatulas to thoroughly mix the two parts of the silicone together. Metal tools can sometimes inhibit cure, so avoid them. You’ll need a tool that can reach the bottom and sides of the container while mixing.
Scale
A digital kitchen scale is extremely helpful for precisely measuring out the two parts of the silicone by weight. Volume measurements by cup or tablespoon are less accurate. Make sure your scale can handle the weight of the silicone needed.
Calculating Silicone Needed
The amount of silicone needed depends on the volume of the mold. To calculate the volume, you need to determine the total cubic inches of the mold container and the cubic inches of the master model.
The basic formula is:
(Mold Container Volume – Master Model Volume) x Waste Factor = Total Silicone Volume
To find the mold container volume, measure the length, width and height of the container in inches and multiply them together. For the master model volume, measure the model’s dimensions and calculate its cubic inches the same way.
A waste factor accounts for silicone that sticks to containers and tools. Use a waste factor of 1.1-1.3. So if your calculations show you need 20 in3 of silicone volume, multiply it by 1.2 = 24 in3 of silicone required.
There are ~21 grams of silicone per cubic inch. So in the example above, 24 in3 x 21 grams/in3 = 504 grams of silicone required. Refer to silicone packaging for exact ratio information.
Online silicone calculators like this one can help determine the measurements and do the math for you.
Mixing the Silicone
When mixing silicone to make molds, following the manufacturer’s instructions precisely is crucial for getting the right consistency and cure. Pay close attention to the specified mix ratio of base silicone to catalyst. Measure out each component carefully using a scale or cups designed for that ratio. Mixing in too much or too little catalyst can prevent the silicone from setting up properly.
To avoid air bubbles in the cured silicone, mix the components thoroughly in a manner that minimizes whipping air into the liquid. Use smooth, gentle stirring motions rather than vigorous whipping or shaking. Scrape the sides and bottom of the mixing container several times to ensure even mixing. Let the mixture sit for a few minutes so bubbles can rise to the top before pouring.
Pouring and Curing
When pouring silicone into the mold frame, it’s important to avoid creating air bubbles. Pour slowly and steadily in one corner, allowing the silicone to spread out and push air ahead of it. Once the mold is filled, use a toothpick or skewer to pop any visible bubbles.
Make sure to seal all edges where the silicone meets the sides of the mold frame. This prevents leaks which can ruin the mold. Run an applicator or your finger along each edge to create a tight seal.
Silicone rubber usually takes 24-48 hours to fully cure. Follow the cure time recommended by the manufacturer, as going too soon can tear the mold when demolding. Once fully cured, flex the mold to break the seal and gently work it off the original model. Avoid using force or tools which could damage the mold surface.
For quicker demolding, consider spraying the model with a release agent first so the silicone won’t grip as tightly. Just make sure to follow safety precautions when using chemicals.
Now you have a completed silicone mold ready for casting resin, wax, or other materials! Store it safely so the surface doesn’t get damaged before first use. With proper care, a high quality silicone mold can be used for many castings.
Source: https://formlabs.com/blog/how-to-make-silicone-molds/
Mold Release Agents
Mold release agents are an essential supply when working with silicone molds. They prevent the silicone from sticking to the mold model or master so you can demold your finished pieces cleanly. There are a few main types of mold release agents to consider:
Silicone-based sprays – These create a thin layer of silicone on the mold surface and are easy to apply. They offer multiple releases before needing to reapply. A popular option is Mann Ease Release spray (https://www.smooth-on.com/products/ease-release-200/).
Water-based sprays – Made from natural ingredients, these are food-safe options good for candy or chocolate molds. They may need more frequent reapplication than silicone versions. An example is Hurricane Spray (https://www.tkbtrading.com/products/hurricane-spray).
Wax or grease – Petroleum jelly, PAM cooking spray, or candle wax can work in a pinch. Reapplication is often needed after every use. Not ideal for intricate molds.
Application depends on the product, but typically mold release is sprayed or brushed in a thin, even layer and allowed to dry before pouring silicone. Too much can lead to cured silicone that is tacky or inhibited. Follow manufacturer guidelines and reapply as needed between uses.
Using the Finished Mold
Once your silicone mold is fully cured and ready to use, you have many options for casting materials. Some of the most popular options include:
- Resin – Both epoxy and UV-curing resins can be cast into silicone molds. Make sure to use proper mold release agents. Resins allow very precise reproduction of details in the mold. See this video for tips on casting resin in silicone molds: How To BAKE With SILICONE MOLDS!
- Chocolate – Tempered chocolate can be poured into silicone molds to make detailed chocolate candies and decorations. Silicone holds up well to the heat of liquid chocolate.
- Candle Wax – Silicone can be used to make custom candles, capturing intricate designs and shapes.
- Concrete – Some makers use silicone molds for small concrete casting projects, like figurines and decorative objects.
With proper care, a silicone mold can be used for dozens or even hundreds of casts before wearing out. Avoid tearing or cutting the silicone. Certain casting materials like concrete can shorten the lifespan of molds compared to softer materials like resin or chocolate. Check your mold periodically for degradation and replace once the fine details are no longer being accurately reproduced.
Troubleshooting
When working with silicone molds, there are a few common issues that can arise, such as tears, deformities, and adhesion problems. Here are some tips for preventing these problems:
To prevent tears, make sure to pour the silicone slowly and gently into the mold frame. Pouring too quickly or from too high up can cause bubbles and rips in the silicone as it cures. It’s also important not to overstretch the silicone by trying to spread it too thin. Follow the manufacturer’s recommendations for pour depth.
Deformities like uneven textures or warped molds can happen if the silicone isn’t fully supported as it cures. Make sure to brace or contain the back and sides of the mold so the silicone cures evenly. You can use boards, clay, or other materials to hold the sides in place.
To prevent baked clay from sticking in the mold, be sure to use mold release spray or oil before each use. Let it dry completely before pouring in clay. Not using enough release agent is a common cause of adhesion issues. It also helps to make sure clay is fully cured before unmolding.
Additionally, carefully pry sculptures out of molds in thin sections rather than tugging. If adhesion persists, put the mold in the freezer for 15-30 minutes before trying again. This will contract the silicone away from the clay.
For more tips, see this tutorial: https://www.youtube.com/watch?v=DHPSxeKsXPI
