I have an old forge made of KAST-O-LITE with a destroyed floor from borax. I was thinking of whether I could recycle it to use as an underlayment for metal casting tasks. Instead of sand I was thinking of taking the old castable and crushing it with a sledge hammer. Theorectically I would end up with refractory gravel that might be a great base for putting hot things on or pouring molten brass over. Any thoughts as to whether this is a viable idea ?

I have an old forge made of KAST-O-LITE with a destroyed floor from borax. I was thinking of whether I could recycle it to use as an underlayment for metal casting tasks. Instead of sand I was thinking of taking the old castable and crushing it with a sledge hammer. Theorectically I would end up with refractory gravel that might be a great base for putting hot things on or pouring molten brass over. Any thoughts as to whether this is a viable idea ?

We used to crush refractory all the time to make mortars and castables for kilns and foundries. It makes the castable lighter, better insulated and help it to survive the heat cycling expansion. There are probably some recipes on some of the ceramics websites. It may be referred to as "grog" in the recipes. Hope that helps!