What is the current thinking on clay plugs for closing staybolt telltales? If your using a pyro brick mortar like seraset are you sure that it doesn't somewhat fuse to the metal and then won't come out if the bolt cracks or breaks? Have you tested any of these materials to make certain that they will function correctly. I know that the brick mortars will become fairly vitrified under high heat.

I have read that the back shops used a preformed tapered clay plug and inserted these into the telltale and then broke off the excess. By inserting a dry tapered clay plug you were assured of somewhat of a mechanical seal rather than using wet brick mortar which adheres to the metal by a chemical action as well as mechanical.

So with this does anyone have any clay formulas for clay plugs? I think what is needed is a clay formulation that will not fully mature at operating temperature. If it does mature then it is getting somewhat liquid and will adhere then plugging the telltale so it is ineffective. Any thoughts on this? Any experience in formulating or forming plugs?