I recently obtained a vacuum chamber and pump to get the air out of my silicone rubber. When I vacuum the material (after mixing Parts A + B), my silicone takes forever to de-air and I still end up with some bubbles in my silicone rubber. Is this normal?

Article courtesy of Smooth-On, Inc.

This symptom likely indicates that your vacuum pump is not pulling enough of a vacuum to quickly and efficiently get the air out of your silicone mix. After your mixing container is placed in the vacuum chamber and the vacuum pump is turned on, the rubber should rise, break and fall in less than 5 minutes.

Minimum Vacuum Pump Rating: Your vacuum pump should be rated to pull 29 inches of mercury (also measured as "-1 Bar") at 8 CFM. Any less than this is counterproductive, as you are enlarging the entrapped air bubbles rather than evacuating them.


This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.