Working Potters ITC formula.
I put this over the castable in my throat arch- a place that takes a real beating. Al Tennant has also used it on his train kiln and the one he built for Amy Kiline at Pottery West. He swears by it. (If you know Al he swears most of the time.)
Coating 2 parts Alumina Hydrate 2 parts 35 mesh Kyanite 2 parts Zirconium (Zircopax, Opax)this is expensive!
1 part Vee gum T
I use weight and not volume Bon feu! Tony Clennell