cast-able refractory is soft and flake off easily it is a good insulator for your furnace if applied several inches thick, you should use some type of support, like pieces of thick wire welded to your furnace wall, or some type of screen wire screwed or riveted in spots to your furnace wall, as support (kind of like re-bar in concrete), also you should use a wash coat of refractory mortar on the outside surface, like Sairset, it will cook hard and form a solid crust on the surface of the walls (kind of like hardened stucco, and withstand a higher temperature, than the cast-able refractory would alone, and can handle the flames of your burner better, to repair the furnace you will remove the flaked washcoat, cut grooves into any cracks of the cast-able refractory and apply another wash-coat of Sairset.
