What is the best method for mixing mold rubber?

There are many factors that can contribute to mold rubber not curing including cold temperatures, contaminants on a model’s surface, etc.

But the most common reason: inadequate mixing of Parts A & B. People mixing rubber for the first time tend to under-mix the material before applying. It is especially easy to under-mix thick materials like silicone or brush-on rubber. Mixing large volumes of material also poses the risk of inadequate mixing. 

Mixing Success: A Function Of Time & Technique - Time - Most mold rubbers give you plenty of time to mix and apply, so don’t worry about not having enough time. Your goal in mixing is to be thorough, not fast. 

Technique: Don’t Be Casual, Be Aggressive - This is where most “first timers” make the fatal mistake of using a “limp wrist”, meaning that they are not aggressive enough in mixing the rubber. Use a stiff mixing paddle and employ a firm wrist, making sure that you scrape the sides and bottom of your mixing container several times. Important material hides on the bottom and sides of your mixing container and failure to get this material into the mix will result in the rubber not properly curing.

The Best You Can Do -

“The Double Mix-And-Pour” Technique - After mixing thoroughly for 3 minutes, empty the contents of your mixing container into a second clean mixing container and mix again for another 2 to 3 minutes before applying over your model. This technique is your best bet for successful mixing and the protection of your mold rubber investment.

Mixing Large Amount Of Rubber Using A Mechanical Mixer?

If using a drill with a “Squirrel Mixer” or other attachment to mix large amount of rubber, mix Parts A & B for 3 minutes at a low RPM. Take a mixing paddle and scrape the sides and bottom of your mixing container several times. Important material hides on the bottom and sides of your mixing container and failure to get this material into the mix will result in the rubber not properly curing.

Empty the contents of your mixing container and use the drill to mix again for another 2 minutes. Use the paddle to again hand mix (scrape the sides and bottom of your mixing container several times) for 2 minutes and apply over your model. This technique is your best bet for successful mixing and protection your mold rubber investment.

Disclaimer
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.