- When casting a large mold, platinum cure silicone is a better option than tin cure silicone.
Tin cure silicone tends to shrink after curing (~0.3%), which becomes more pronounced in larger molds. In contrast, platinum cure silicone does not shrink upon curing, maintaining a stable size throughout. - If you choose to use tin cure silicone for a large mold, here are some key suggestions:a) Don’t add too much hardener: Excess hardener causes the silicone to cure too quickly, leaving you with insufficient time to pour it. We recommend a mixing ratio of 100 parts silicone to 2-3 parts hardener by weight (not by volume). If the curing time is still too fast, you can try reducing the hardener to 1-1.5% of the silicone weight. You can control the pot-life (working time) by adjusting the hardener ratio—less hardener results in a longer pot-life, and more hardener shortens the pot-life.b) Use a mold release agent on the original model. Suitable release agents include wax, petroleum jelly (Vaseline), or soapy water.c) Vacuum degassing is essential before pouring the silicone. Failing to degas will trap bubbles in the mold, which weakens the mold’s structure and can distort fine details from the original model.d) Ensure the mold is thick enough for optimal strength. A general guideline is that the mold should be at least 3 cm thick.
By following these steps, you can improve the quality and durability of your large silicone mold.