What is the best method for mixing rubber?
The "Double Mix-n-Pour" Technique.
There are many factors that can contribute to a rubber not curing properly such as cold temperatures and interraction with contaminants - both of which will cause a "cure inhibition". But the most common reason why an RTV rubber (urethane & silicone) will not cure properly is INADEQUATE MIXING of Parts A & B.
People mixing rubber for the first time tend to "under-mix" the material. It is especially easy to under-mix high viscosity (thicker) materials like silicone. Mixing large volumes of material also poses the risk of inadequate mixing.
** Mixing Success: A Function Of Time & Technique **
TIME: Most RTV rubbers give you plenty of time to mix and apply, so don’t worry about NOT having enough time. The goal in mixing is to be THOROUGH, not fast.
TECHNIQUE: Don’t Be Casual, Be Aggressive. This is where most “first timers” make the mistake of using a “limp wrist”, meaning that they are not being aggressive enough in blending the the rubber components. Use a rigid mixing spatula (metal recommended) and employ a firm wrist, making sure that you SCRAPE THE SIDES & BOTTOM of your mixing container several times.
Unmixed material hides on the bottom and sides of your mixing container and failure to get this material thoroughly blended into the mix will result in the rubber not properly curing - which is a form of inhibition.
** The Best You Can Do - Protect you Investment of Time & Materials **
The "Double Mix-n-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.
This proven technique is the best way to ensure thorough, successful mixing.
** 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.
(Note: As mentioned above, unmixed material hides on the bottom and sides of your mixing container. Failure to get this material blended 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.
(Note: Drill mixing will introduce air bubbles into the mixed material. While not required, vacuum degassing the mixed rubber will reduce the possibility of entrapping air bubbles.)