Can I Use Any Silicone To Make Molds?
Silicone mold making has become increasingly popular in recent years among hobbyists, crafters, and manufacturers. Silicone is highly valued for its flexibility, durability, and ability to reproduce fine details, making it an ideal material for casting and mold making. The process of making silicone molds involves mixing and pouring a liquid silicone that cures into flexible rubber. Silicone molds have many advantages over traditional mold making materials like plaster or clay. They are extremely durable, able to withstand high temperatures, flexible for releasing cast parts, and make it easy to reproduce complex 3D forms.
The popularity of silicone mold making has grown steadily over the past decade. Silicone is now widely used for a variety of mold making applications across many industries including manufacturing, cooking, arts and crafts, and special effects. The versatility and reusable nature of silicone has made it accessible and practical for both large-scale production runs as well as small hobby projects. With some basic materials and proper techniques, it is relatively easy to create accurate silicone molds at home.
Types of Silicone
There are two main types of silicone used for mold making: tin cure and platinum cure. The main difference between them is the curing process.
Tin cure silicone uses a tin-based catalyst to cure the material. It cures faster than platinum silicone, usually within 24 hours. Tin cure molds have a lower tear strength and shorter library life compared to platinum. However, tin cure silicone tends to be less expensive (source: https://puduoresin.com/2022/09/08/silicone-mold/).
Platinum cure silicone uses a platinum-based catalyst for curing. It has a longer working time, curing in 48-72 hours. Platinum cured molds have higher tear strength, heat resistance, and longer library life than tin cure. However, platinum silicone tends to be more expensive (source: https://www.temu.com/silicone-for-mold-making-s.html).
Overall, platinum cure silicone is preferred for mold making because of its superior durability and reuse potential. Tin cure works well for simpler molds and quick turnaround times. The type used depends on the specific project needs and budget.
Factors to Consider
When choosing a silicone for mold making, there are several key factors to consider:
Tear Strength
Silicone’s tear strength determines how easily it can withstand tearing or ripping during demolding. A high tear strength over 500 PSI is ideal for complex molds.
Viscosity
The viscosity or thickness of the uncured silicone determines how well it flows into intricate mold details. Low viscosity silicones around 5,000 cPs work well for picking up fine textures.
Shelf Life
Make sure to choose a silicone with at least a 6 month shelf life. Condensation cure silicones last longer than addition cure types.
Flexibility
Flexible, stretchy silicone is essential for removing castings from molds. A Shore A hardness around 20-30 provides good flexibility.
Food Safety
Always verify the silicone is food-safe if making molds for edibles. Platinum cure silicone is the most inert and non-toxic option.
Other considerations include cure time, shrinkage, cost, transparency, and compatibility with mold release agents.
Best Silicones for Molds
When selecting the best silicone for making molds, it’s important to consider factors like hardness, tear strength, flexibility, and viscosity. Some of the top recommended silicones for mold making include:
Dragon Skin – This platinum-cure silicone has high tear strength and flexibility, making it ideal for complex molds. It has a Shore A hardness of 10 and can pick up fine detail. Dragon Skin is versatile and works for a variety of applications.
OOMOO – Formulated for rapid mold making, this tin-cure silicone has a low viscosity for excellent flow and pickup of detail. It cures quickly into durable, flexible molds good for casting resin, wax, concrete, and more. OOMOO has a Shore A hardness of 25.
Mold Max – This condensation-cure silicone has high heat resistance while maintaining flexibility and elongation. It can withstand up to 490°F. Mold Max has versatile 1:1 mix ratio and is a popular choice for mold making beginners due to its ease of use.
Other excellent mold making silicones include Sorta Clear for transparent molds and Body Double for life casting and body part molds. When selecting a silicone, consider the type of mold, level of detail required, casting material, mold longevity, and cost.
Proper Use
When working with silicone to make molds, proper measuring, mixing, pouring, and degassing techniques are crucial for achieving the best results. Here are some tips for proper use:
Measuring – Carefully measure out equal parts of Part A and Part B silicone according to the manufacturer’s instructions using a scale or measuring cups. The exact 1:1 ratio is critical.
Mixing – Thoroughly mix together Parts A and B, scraping the sides and bottom of the container at least 3-4 times. Mix for 3-5 minutes to ensure it is fully incorporated with no streaks.1
Pouring – Slowly pour the mixed silicone over the object being molded, starting from one edge to prevent air bubbles. Pour from a height of 6 inches or less. Tap the mold to release any trapped air bubbles.
Degassing – Use a vacuum chamber to remove air bubbles and impurities, if available. Let the poured mold sit for 5-10 minutes before degassing to allow bubbles to rise to the surface.
Properly following these techniques will help create a smooth, even mold free of defects.
Mold Making Process
Making a simple silicone mold is a straightforward process that involves a few key steps:
1. Prepare the master model. This is the object you want to make a mold of. It should be made of a non-porous material like metal, plastic, or glass. Make sure the model is clean and free of debris before molding.1
2. Build a container around the object. This will hold the liquid silicone as it cures. Use Legos, clay, or other materials to construct walls around the master model with at least 1 inch clearance on all sides.2
3. Prepare the molding silicone. Mix the two silicone components together as directed. Stir thoroughly to activate the curing process. Act quickly as silicone will start to cure in 5-10 minutes.
4. Pour the silicone. Slowly fill the container, pouring over the master model. Tap the container to release air bubbles. Fully cover the object with 1/2-1 inch of silicone.
5. Allow silicone to cure. This usually takes 6-12 hours. Do not disturb the mold during this time.
6. Remove master model. Carefully deconstruct the container and peel the silicone mold away. The master model can now be removed.
7. Finish mold. Trim excess silicone and create pour holes if needed. The flexible mold is now ready to cast resin or other materials.
Troubleshooting
Making silicone molds can be tricky, and problems can arise even for experienced mold makers. Some common issues and solutions include:
Bubbles – Bubbles in the cured silicone indicate that air was introduced during mixing. To prevent bubbles, mix thoroughly but gently, avoid whipping or agitating the silicone, and tap the mold to release bubbles before curing. Degassing the mixed silicone in a vacuum chamber also helps prevent bubbles.
Inhibition – Certain materials like sulfur clays can inhibit silicone from curing properly, leaving tacky spots. Use a barrier like PVA tape around clay originals when molding. Test materials first before molding.
Uncured silicone – Silicone may not fully cure if ratios are off, if not enough catalyst was used, or if pouring very thick layers. Follow manufacturer ratios exactly, only use fresh catalyst, and pour in thin layers when possible. Allow extra cure time if needed.
Sources:
https://www.youtube.com/channel/UCbZxxVU9QrEnwXL4iymHIHA/videos
Mold Release Agents
Mold release agents are an important part of the mold making process. They serve several key functions:
- Allow easy demolding – Mold release agents prevent cured silicone from sticking to the mold. This allows you to easily separate your finished casting from the mold.
- Extend mold life – Release agents lower the friction required to remove castings, reducing wear and tear on the mold over time.
- Improve surface finish – Mold release agents can impart a smooth, glossy finish to castings.
When choosing a release agent, opt for products specifically formulated for mold making. These are designed to work with silicone rubbers. Some popular options include:
- Mann Ease Release spray – An aerosol silicone release ideal for quickly prepping molds.
- Smooth-On Universal Mold Release – A liquid release agent that produces a semi-permanent coating for multiple demoldings.
- Ease Release waxes – Provide a layer of wax to facilitate demolding.
Be sure to apply mold release agents according to the manufacturer’s directions. Typically a light, even coat on all mold surfaces is recommended before each casting. Proper application is key to realizing the full benefits of mold release products.
Safety Tips
When working with silicone mold making materials, there are some important safety precautions to take:
Wear protective equipment like gloves, goggles, and a respirator mask. The fumes from silicone can be irritating to eyes, skin, and lungs.
Work in a well-ventilated area to allow fumes to dissipate. Consider working outdoors if possible.
Read product safety datasheets so you understand any potential hazards or special handling instructions.
Avoid contact with skin as much as possible. Use long sleeves and pants. Wash hands thoroughly after use.
Store silicones securely, out of reach of children and pets. Some silicones use tin catalysts which can be toxic if ingested.
Take care mixing and pouring to avoid spills. Silicone can be slippery and difficult to clean thoroughly.
Dispose of used silicone containers properly. Check local regulations as they may require special hazardous waste disposal.
Always follow the silicone manufacturer’s specific safety recommendations.
With proper handling, silicone mold making can be done safely. But understanding the risks allows you to work cautiously.
For more tips, see this helpful safety overview: https://www.reddit.com/r/ResinCasting/comments/ty7jn0/silicone_moldmaking_safety/
Conclusion
When choosing a silicone to make molds, it’s important to consider the type of silicone, desired curing time, shelf life, hardness, tear strength, and heat resistance needed for your application. The best silicones for mold making often have good flowability for capturing detail, while also being strong and durable. Popular choices include platinum-cure silicones, tin-cure silicones, and condensation-cure silicones. Each has their own advantages and disadvantages.
Properly following the mold making process will help ensure you end up with a high quality mold. This includes proper surface preparation, mixing and degassing the silicone, pouring it slowly over your original pattern, and allowing time to fully cure before demolding. Using a release agent can further help prevent silicone sticking.
With some care taken during the process, silicone molds can capture fine details, last through many castings, and provide reliable reproductions. This guide covered the key factors in selecting and working with silicone for DIY mold making. For more details on specific products or mold making techniques, consult manufacturer technical data sheets and mold making reference books.
