Home made high temp castable refractory

[Buzzkill]

I made something quite similar.  I used fire clay, white (silica) sand, styrofoam, and Greenpatch 421.  This was nearly 3 inches thick in my forge and it would take over an hour of operation before the outer shell got too hot to comfortably lay your hand on it.  However, as I look back on it now, I would recommend just buying a quality insulating blanket material and a good refractory for the hot face. You'll save yourself a lot of time, effort, and probably money in the long run.   My refractory mix worked, but was very heavy (my forge weighed as much as my anvil), and after use it took a couple hours to cool down to the point where I was comfortable handling it.  There is a reason that some things have become a standard.  This usually happens when lots of people try lots of ideas and a large number of them come to the same conclusion after the experimenting is done.  Take it for what it's worth.

[Nobody Special]

The various clay/sand mixes work fine for lining coal/charcoal forges. I've tried different things in the mix, grasses, wood chips, sawdust, perlite, vermiculite, busted pottery for grog, haven't messed with foam beads. Grass and wood chips seem to give it the most cohesion, not sure that it makes it a better refractory.

 I wouldn't mess with it for propane. Too heavy, too crumbly, and I doubt it's as effective a refractory.

The backyardmetalcasting mix with the portland works well for a small casting furnace up to brass pouring temps, (around 2100 to 2200F) but not so much in a forge. It gradually spalls further and further away from the firepot, effectively leaving you with a big duck's nest forge. It's made worse by the fact that clinker sticks to it and has to be chipped off.

[Frosty]

Other than making a kiln wash for the fire contact area commercial insulating refractories are superior. They have labs and competitors to drive them to excell for our dollar. Let them do the brain work they don't really charge us that much for all the work.

Even my original pipe forge, yeah, 10.5" dia. 3/8" wall pipe shell. (Yeah, I made one too and it's one of several incarnations of propane forge that live in or around my shop) It has an inner liner of Pyramid Super, Air set rammable refractory 3/4" thick. I truly wish Pyramid was still in business and this refractory still available, it's a high phosphate, phosphate bonded refractory rated to be concrete hard and tough at 4,200f. Phosphate doesn't notice borax at any temperature, this stuff was designed to line furnaces that operated with a 4,000f ammonia atmosphere.

Anyway, the Pyramid hard inner liner had a 1" 8lb. Kaowool insulating outer layer. Being as it was fired with my first successful T burner build it had a 1" T in just 340 cu/in. It'd get hot enough to melt 5/8" sq. steel stock RR spike you know, in under 1 minute. I kept it seriously turned down. At melting temps it'd take about 2 hrs to heat the shell so you couldn't lay your hand on it and never got boiling hot.

I know that was WAY long. At present I'd use 2" of 8lb. Kaowool or the equivalent. Rigidized for strength and particle encapsulation then wash it to maybe 3/4" on the floor and around 1/2" on the walls and roof. The final wash would contain significant zirconium silicate whether a commercial product or maybe my recipe, IF it works.

Frosty The Lucky.

[Charlotte]

Forget plastic  foam.  the pearlite used for drainage in garden and potting soil is a slightly better bet.  However,  insulate with insulating blanket or brick is the practical alternative. The other materials do not really work.

The clays are available on line or from local suppliers to industry or more commonly  from ceramic suppliers in the local area.  You really need to read the information stickies  in the Gas forge forum.   There is a wealth of practical information free for the effort of reading;