This kiln was cast from a novel material that exhibited admirable firing qualities it also reused and made inert a rather noxious waste material . I was given a large but crumbling and  worn out fibre kiln. I made a slurry of the fibre (a terrible job) and combined this with high alumina ciment fondue and sand and some foam beads. After curing and firing the material resemble soft firebrick on the inside of the kiln and hard concrete on the outside. The kiln lives outside and is impervious to the weather. I modified the flue and burner port along the way as my original concept of flues travelling up through the walls from the floor didnt work very well When we moved house the kiln was pretty severely damaged  but I just reassembled the pieces  and it works ok. If and when I do this again I would do things a bit differently. I would use perlite instead of sand and foam beads and some  steel mesh in the arch would be good, but not to near the hot face.