Can I grind up old silicone and add it to new silicone?

Article courtesy of Smooth-On, Inc.

Some people re-use silicone in this way; however, there are a few challenges with this method you should be aware of.

  • Residue from release agents, etc. may contaminate the silicone, meaning the silicone would need to be thoroughly washed with a solvent before cutting it up.
  • Cured silicone may not bond to new silicone, meaning silicone made incorporating old silicone will have a lower tear strength because the piece of cured silicone may not bond to the curing liquid.
  • Inhibition risks are greatly increased when doing this, as there may be contaminants or incompatible chemical formulations at work.

In short, it is a risky proposition to incorporate old silicone into new.


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.