Hmmm... that really sucks to have a busted kamado. From everything I've learned in ceramics classes, the most critical part of this equation is removing all of the air from the plaster of Paris. If there are any air pockets, it can explode when hot. This happens very often when doing a kiln firing. Undoubtedly, if you have a masterpiece, some rookie will have a piece explode in the kiln and wreck your piece. In ceramics, we kneed the clay like bread, not sure about plaster. Maybe vibrate it a lot. Good luck!