Hi Alan, good work there, it seemed to work really well given the damage etc.

I have not built a furnace yet but from the research I have done so far I think if anything you may need more fire clay and less silica.

It looks as if the silica sand has melted to form glass inside the furnace. I believe clay can withstand temperatures of more than 1500 degC.

I am going to try a mix of Cement 1 part, clay 3 parts, sand 1 part and six parts Perlite.

As I said, I have never done this before but I cant wait to try it.

I would be interested to know your thoughts on this.

Try papercrete. It insulates well and is fireresistant.

Try mixing ceramic microspheres with a small batch of cement to use as athermally reflective paint on the interior of your furnace