Step 7: Mix molding compound
Try to keep the beaters below the surface of the water to avoid adding more air to the mixture as this will result in bubbles in your mold.
Also do not beat the mixture for more than 45 seconds or so. Remember that this is a 3 minute cure molding compound. If you mix for too long you'll end up with a bad mold. Don't worry if the mixture still looks lumpy and not completely mixed.
If you have a vacuum chamber you can remove some of the bubbles from the molding compound by pulling a light vacuum from it. It may foam up, so be prepared with a large container, or a willingness to clean up a mess.
Alternately, firmly rapping the container against the table should bring up many bubbles as well.