I've got an old water boiler furnace. There's a crack in the outer metal of it. You can see the flames by the crack and the metal becomes orange when it's hot. I asked advice to a technician on how to fix this and he said that usually they put a fire proof panel over the crack from the inside of the furnace. They use some kind of cement to "glue" the panel.

Do you know what are the exact names for these materials (the panel and the cement) and where they are available for purchase?