Earlier this year we put together a kiln to melt some aluminum and the lid we made was good enough, but not perfect. It was made of soft refractory bricks, held to a metal plate with fireplace adhesive. The adhesive failed so this time we decided to cast a lid in refractory cement. This video shows the casting process and testing process. There was a lot of cement left over so we smeared in on the inside of the kiln. One lesson we learned is that a thin layer of cement will crumble at the temperatures we use in our kiln.