I'm not familiar with ITC-100HT Ceramic Coating but when I built my propane tank foundry all I used was 1" kaowool under my homemade refractory. Why would you need to protect your refractory from the heat? Isn't its purpose to withstand the high temperatures? I apologize if I misunderstood or if I'm not smart enough to answer your question. But for what it's worth, I got a 3' x 4' sheet on ebay for around $40. Which was almost twice what I needed for my 5lb propane tank foundry. There's a great 3 part tutorial on youtube by rlbob1 called Backyard Foundry Tutorial. Hope this helps. Good luck!