Silicone is a versatile material that can be used for making molds and casting resin. It has many advantages over other types of molding materials, such as latex, alginate, or plaster. Silicone is flexible, durable, easy to work with, and can produce high-quality results. However, silicone molding also has some challenges and requires some skills and knowledge to master. In this blog post, we will share with you some essential tips and techniques for beginners who want to learn how to use silicone for molding and casting.

What is Silicone and How Does It Work?

Silicone is a synthetic polymer that consists of silicon, oxygen, and other elements. It can be classified into two main types: addition cure and condensation cure. Addition cure silicone is also known as platinum cure silicone because it uses platinum as a catalyst to initiate the curing process. Condensation cure silicone is also known as tin cure silicone because it uses tin as a catalyst. The curing process is the chemical reaction that transforms the liquid silicone into a solid rubber.

The main difference between addition cure and condensation cure silicone is that addition cure silicone does not produce any by-products during the curing process, while condensation cure silicone produces alcohol or water as a by-product. This means that addition-cure silicone has less shrinkage, higher tear strength, longer shelf life, and better resistance to high temperatures than condensation-cure silicone. However, addition cure silicone is also more sensitive to contamination, more expensive, and has a shorter working time than condensation cure silicone.

Another way to categorize silicone is by its viscosity, which is the measure of how thick or thin it is. Viscosity affects how easy it is to mix, pour, and degas the silicone. Generally, lower-viscosity silicone is easier to work with, but it may also capture more air bubbles and require more release agents. Higher viscosity silicone may be harder to work with, but it may also produce fewer air bubbles and require less release agent.

Some common types of silicone that are used for molding and casting are:

RTV-2 (Room Temperature Vulcanizing) silicone: This is a type of addition cure or condensation cure silicone that can cure at room temperature with negligible shrinkage. It is ideal for making molds of complex shapes and fine details.

Putty silicone: This is a type of condensation cure silicone that has a clay-like consistency and can be kneaded by hand. It is ideal for making molds of simple shapes and large objects.

Translucent silicone: This is a type of addition cure or condensation cure silicone that has a clear or semi-transparent appearance. It is ideal for making molds of objects that need to be visible through the mold or for casting translucent resin.

Skin-safe silicone: This is a type of addition cure or condensation cure silicone that has been tested and certified to be safe for direct contact with human skin. It is ideal for making molds of body parts or prosthetics.

How to Choose the Right Silicone for Your Project?

Choosing the right silicone for your project depends on several factors, such as:

• The shape, size, and detail of the object you want to make a mold of
• The type of resin you want to cast in the mold
• The budget, time, and equipment you have available
• The level of experience and skill you have with silicone molding

Here are some general guidelines to help you choose the right silicone for your project:

• If you want to make a mold of an object that has complex shapes and fine details, such as jewelry or figurines, you should use RTV-2 silicone with low viscosity and high tear strength.
• If you want to make a mold of an object that has simple shapes and large dimensions, such as furniture or sculptures, you should use putty silicone with high viscosity and low tear strength.
• If you want to make a mold of an object that needs to be visible through the mold or cast translucent resin in the mold, you should use translucent silicone with low viscosity and high tear strength.
• If you want to make a mold of a body part or prosthetic, you should use skin-safe silicone with low viscosity and high tear strength.

How to Prepare the Object for molding?

Before you start making the mold, you need to prepare the object that you want to make a mold of. This involves:

Cleaning the object

• Remove any dust, dirt, grease, or wax from the surface of the object using soap, water, or alcohol.
• This will ensure that the silicone adheres well to the object and does not capture any unwanted details.

Sealing the object

• Seal any porous or absorbent surfaces on the object using acrylic paint or spray sealer.
• This will prevent the silicone from soaking into the object and causing bubbles or distortion in the mold.

Applying release agent

• Apply a thin layer of release agent to the surface of the object using a brush or spray.
• This will prevent the silicone from sticking to the object and make it easier to de-mold.
• You can use different types of release agents, such as petroleum jelly, wax, or silicone spray, depending on the type of silicone and resin you are using.

How to Mix and Pour the Silicone?

After you have prepared the object for molding, you need to mix and pour the silicone. This involves:

Measuring the Silicone

1. Use a weighing scale or a measuring cup to measure the amount of silicone you need for your mold.
2. Follow the instructions on the packaging of the silicone for the correct mixing ratio of the base and the catalyst.
3. Account for some extra silicone for spillage or leakage.

Mixing the Silicone

1. Thoroughly mix the base and the catalyst of the silicone using a wooden stick or a spatula in a clean plastic or metal container.
2. Scrape the sides and bottom of the container to ensure that there are no unmixed parts.
3. Avoid mixing too fast or too vigorously to prevent creating air bubbles in the silicone.

Degassing the Silicone

1. Remove any air bubbles from the silicone using a vacuum chamber or a pressure pot.
2. This will improve the quality and accuracy of your mold.
3. If you do not have access to this equipment, you can also tap or shake the container gently to release some of the air bubbles.

Pouring the Silicone

1. Slowly and steadily pour the silicone over the object in a thin stream from a high position.
2. This will help reduce air bubbles and ensure even coverage.
3. Start from the lowest point of the object and work your way up.
4. Make sure that there are no gaps or undercuts in the object that may trap air or silicone.

How to Cure and Demold the Silicone?

After you have poured the silicone, you need to cure and de-mold it. This involves:

Curing the silicone

Before demolding the silicone, you must allow it to cure completely. The curing time depends on the type and thickness of the silicone, as well as the temperature and humidity of the environment. You should follow the instructions on the packaging of the silicone for the recommended curing time and conditions.

You can also use a heat gun or a hair dryer to speed up the curing process. However, be careful not to overheat or burn the silicone.

Demolding the silicone

Once the silicone has cured, you can begin the demolding process. First, carefully peel off or cut away any excess silicone from around the object. Then, gently pull or pry the silicone mold away from the object, starting from one corner or edge. Be careful not to damage or tear the mold or the object.

How to Use and Store Your Silicone Mold?

After you have made your silicone mold, you can use it for casting resin or other materials. To do so, you need to:

Cleaning and drying your mold:

• Clean your mold after each use with soap and water or alcohol.
• Remove any residue or debris from the mold with a soft brush or cloth.
• Dry your mold completely with a towel or hair dryer.

Applying release agent:

• Apply a thin layer of release agent to your mold before each casting.
• This will prevent your casting material from sticking to your mold and make it easier to de-mold.
• You can use different types of release agents, such as petroleum jelly, wax, or silicone spray.

Filling and curing your mold:

• Fill your mold with your casting material according to its instructions.
• Make sure there are no air bubbles or gaps in your casting material.
• Let your casting material cure completely before demolding it.

Demolding your cast:

• Carefully peel off or cut away any excess casting material from around your mold.
• Gently pull or pry off your cast from your mold, starting from one corner or edge.
• Be careful not to damage or distort your cast or your mold.

Storing your silicone mold:

• Clean and dry your mold as described above.
• Apply a thin layer of talcum powder to your mold using a brush or spray.
• This will prevent your mold from sticking to itself or other surfaces and protect it from moisture and dust.
• Wrap your mold in plastic wrap or a plastic bag and seal it tightly.
• Store your mold in a cool, dry, and dark place away from direct sunlight, heat sources, or sharp objects.

Conclusion

Silicone molding is a fun and rewarding hobby that can help you create unique and personalized objects with resin or other materials. However, it also requires some skills and knowledge to master. By following these essential tips and techniques for beginners, you can learn how to use silicone for molding and casting successfully and safely.