I've been reading through old posts, and ran across a couple mentions of using a sand/fireclay mix behind the hot face and for the floor. I started wondering how insulating this would be compared to other backing material. As mentioned in another thread, I am kicking around the idea of lowering a new waste oil furnace below ground level. I have a large 24" laundry dryer tub which is a bit too large, but if I create a 12-14" burn chamber contained by a 1/2" mizzou hot face, I could simply backfill the remaining 12" with the fireclay/sand mix. Any ideas how well this would insulate compared to the 2" of kaowool I stashed behind the hot face in my current furnace? My goal is to generally stay simple, but sometimes I find that I go too simple, so feel free to jump in and help guide me to a simply great furnace.
My furnace is in a beer keg. 1” mizzou backed by 1.5” sand/fire clay. The first 1/2 hour is spent mostly just getting that rock saturated with heat. Once it’s hot it is quite effective. I don’t think either material conducts heat very well, but they are not insulating. I’m burning mostly free waste oil (some diesel added) so I’m not too worried about fuel consumption, but if I had to do it again I would definitely use the koawool/mizzou combination or possibly koawool/Blu-ram (see Melterskelter’s build). Pete
This makes sense. Based on the posts, I was wondering if the fireclay/sand mixture created some unknown amazing insulation that I wasn't aware of. I recently used my last bit of ceramic wool and was hoping I wouldn't have to order more. Blue-ram looks interesting, but I don't have easy access to it like Mizzou. Then again, I can melt iron with my ragged old Mizzou furnace, so I guess I shouldn't go about fixing something that isn't broken. Thanks
I have two furnaces. One has a Mizzou hot face and three inches of ceramic wool behind it. I would never do that again. Why? The hot face cracks because it is unsupported the furnace is too light and moves around when I handle my #30 crucible with my gantry crane. Pain in the ass. My small furnace uses a Mizzou hot face and a backing of rammed up ditch-bank clay and sand. It is rock solid and has held up for over ten years. If I ever build another furnace, this will be the method I shall use.
I have two furnaces. One has a Mizzou hot face and three inches of ceramic wool behind it. I would never do that again. Why? The hot face cracks because it is unsupported the furnace is too light and moves around when I handle my #30 crucible with my gantry crane. Pain in the ass. My small furnace uses a Mizzou hot face and a backing of rammed up ditch-bank clay and sand. It is rock solid and has held up for well over ten years. I would never use any other method to build a furnace. Richard
