Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
What we do is to route a groove that is about 1/16" deeper than needed to allow space for a gasket. It should also have about 1/16" gap around the outer edge, so make it 1/8" larger in diameter, i.e. 12-5/8".
You can use any number of things for gasket material, felt, cardboard, etc. I prefer to use PVC sheets. You can get it at any hardware store as shower pan material.