Rebuilding furnace, refractory problem, losing too much heat

[Owltech]

1" Kaowool performs MUCH better than 2" Kaowool compressed down to 1"

 

[snoman701]

Depends on the type of plaster, but yes, it can be just calcined lime. Or it can be gypsum.

I wouldn't use any homemade refractory mixes for anything that you need to be reliable.