The rule of thumb is this; silicone bonds to nothing but another silicone, Alumilite (urethane) bonds to everything but silicone! When pouring RTV silicone against any non silicone surface (exception: a porous surface, such as wood, it would need to be sealed, silicone can wick into the pours while curing), mold release is not required. If you are pouring RTV silicone against itself a rubber to rubber mold release is REQUIRED! If you are pouring Alumilite into anything but silicone, a mold release is REQUIRED. The Stoner Urethane Mold Release works very well for non silicone based molds.