Also on these boards
Coat what you want to mold in Vaseline and cover with thick layer of 100% silicone sealant; Let it cure; remove mold and fill with plaster of paris
What the what. So glad I saw this AFTER I just caulked for the first time. So remembering this for whenever I have to caulk anything again: using an ice cube: The caulk will not stick to the ice, and the ice will melt to the shape of the joint to become the perfect shaped tool. Thanks Apartment Therapy!