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The Ultimate Guide to Working with RTV-2 Silicones: Tips and Techniques


If you’re a creative enthusiast or a professional in the world of mold-making and casting, you’re probably no stranger to RTV-2 silicones. These versatile materials are a staple in various industries, from art and sculpture to industrial prototyping. However, to achieve the best results and ensure a successful project, it’s crucial to understand the ins and outs of working with RTV-2 silicones. In this comprehensive guide, we’ll delve into everything you need to know about these remarkable materials.

Part A: Safety First

Before we dive into the nitty-gritty of RTV-2 silicones, let’s start with the basics of safety. Working with any chemicals requires caution and proper protective measures to minimize risks. Here’s what you need to keep in mind:

1. Ventilation Matters

Always work in a properly ventilated area. Adequate ventilation is essential to dissipate any fumes or vapors that may be released during the silicone casting process. Make sure the workspace has “room size” ventilation to ensure your safety.

2. Protective Gear

To minimize the risk of contamination and contact with the material, wear safety glasses, long sleeves, and rubber gloves. However, it’s essential to note that latex gloves can interfere with the curing process of RTV-2 silicones, so opt for vinyl gloves instead.

Part B: Proper Handling and Storage

To ensure the success of your project, you must handle and store RTV-2 silicones correctly. Here are some essential guidelines:

3. Temperature Control

Store and use the silicone material at room temperature, which is approximately 73°F or 23°C. Using it at warmer temperatures can reduce its shelf life. Remember that these products have a limited shelf life and should be used promptly.

Part C: Applying Sealer/Release Agent

Properly applying a sealer or release agent is crucial, especially when working with Tin cure RTV-2 Silicone rubber. Here’s what you need to know:

4. Compatibility Check

Tin cure RTV-2 Silicone rubber may react adversely with sulfur-based clays, leading to tackiness or incomplete curing. To ensure compatibility, perform a small-scale test by applying a small amount of rubber to a non-critical area of your pattern. If inhibition occurs (the rubber becomes gummy or doesn’t cure), use a “barrier coat” of clear acrylic lacquer on the pattern.

5. Release Agent

While not always necessary, a release agent can make demolding easier when casting on various surfaces. Consider using a release agent to facilitate the demolding process.

Part D: Measuring and Mixing

Now, let’s get into the heart of the matter—measuring and mixing the RTV-2 silicones properly is crucial for a successful mold. Here’s a step-by-step guide:

6. Pre-Mix Part B

Before you start, thoroughly pre-mix Part B to re-disperse any pigments that may have settled. This ensures uniformity in your mixture.

7. Precise Measurement

Using a gram scale, dispense the required amounts of both parts A and B into a mixing container. Mix these components for a minimum of 3 minutes, scraping the sides and bottom of the container several times.

8. Vacuum Degassing

To eliminate any entrapped air in the liquid rubber, it’s recommended to use vacuum degassing. Your vacuum pump should pull a minimum of 29 inches of mercury (or 1 Bar / 100 KPa). Vacuum the material until it rises, breaks, and falls. Continue vacuuming for an additional 1 minute after the material falls.

Part E: Pouring, Curing, and Post Curing

The pouring and curing process is critical to achieving the desired results. Follow these steps for the best outcome:

9. Precise Pouring

For optimal results, pour your silicone mixture at a single spot at the lowest point of your containment field. Allow the liquid rubber to find its level and flow over the model uniformly. Ensure that the liquid rubber rises at least 1/2 inch (1.3 cm) above the highest point of the model surface.

10. Curing Time

Allow the mold to cure for a minimum of 16 hours at room temperature (73°F/23°C) before demolding. This curing period is essential to ensure the silicone sets properly.

11. Post Curing

For added assurance and to eliminate any residual moisture and alcohol, post-cure the mold for an additional 4 hours at 150°F (65°C). This step is crucial to ensure the complete curing of certain urethane resins and rubbers. Always allow the mold to cool to room temperature before use, and avoid curing where the temperature is less than 65°F/18°C.


In conclusion, working with RTV-2 silicones can be a rewarding endeavor, provided you follow these essential guidelines. Remember that precision and care are key when handling these materials. By ensuring safety, proper handling, and precise measurements, you’ll be well on your way to creating flawless molds for your artistic or industrial projects. Happy casting!

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