I made a small refractory of perlite and sodium silicate. Thinking the plater of Paris was only to accelerate the drying of the sodium silicate and not having any handy I left it out. Is the refractory useless now?
I don't know that I'd trust it once the temps got up there and sustained. It may be good for lower temps or light duty stuff, I don't know. Plaster of paris is a new combination for me. The one i used was perlite, sodium silicate and aluminum oxide powder. I used a bit more powder than was suggested because it deals with the extreme heat better. Then I used a high temp stove mortar to parge the inside of my forge to cover it all up. It works great but you have to let the stove mortar dry for at least a week or so or it will bubble on you. I had all kinds of little bubbles that burst and left tiny little craters throughout the inside of my forge. It won't win any beauty contests but it works great.
