Was reading through this thread, and Allen..(Hi Allen), said, if we could find a way to form perlite etc etc at 1" thick etc etc, then I had an idea. If how to form perlite, and possibly make it fairly durable as well, idk. Tell me what y'all think? What if wooden forms were built, inside and outside forms with a bottom and top that will hold vacuum, and have air chucks one either end, then perlite was added and just barely packed, just enough to make sure it's even, and without large voids, then water glass was added, using vacuum to evenly distribute it throughout the perlite. You could then burn the forms off, to cure the water glass and make it solid, right? Or am I wrong about water glass being gardens by firing? It's been high school art class since I messed with water glass. I realize it may be sorta fragile, if dropped or something, but so is refractory of any sort really, if it's good. Would water glass be a bad choice due to thermal conductivity? Even if used sparingly, and only enough to cure and hold done perlite together? Maybe 1-1/2" thick instead of 1", due to the silicate binder? Ive made one rocket mass heater, 4" in my basement in my old house, went into hole in existing brick chimney, had 26' of 4" exhaust prior to chimney, 4" j tube, 30 gal barrel. I used old barn wood scraps at first till I ran out of wood I was willing to burn, (I do barn demo), worked good, barrel got glowing hot on top. Then I used pellets so reconfigured the feed tube, and used some thin stainless steel expanded metal for the basket. It melted into droplets and largely burnt away into nothing like the stove piping I used for the inside heat riser form, the barrel was glowing bright orange almost yellow, so I choked it out slowly, which led to a backfire, hot sparks and ashes exploded everywhere, good thing I prepared for the worst and had nothing around, a hose and couple extinguishers nearby, which I didn't use, they were there though cause it was my first stove, was nervous about it. I tried solid 3/8 stainless steel rod, which was very hard to bend into a basket to hold Tony pellets, but I did it, and it only lasted...idk, MAYBE a week, burning 4-5 hrs a night. I had to put a pot of water on the top of the barrel to keep it from getting so hot. It was getting bright yellow, almost to the point of whiteness, so I put a fan over it and a pot of water. The inside of the j tube was breaking apart in like, 1/8" to 3/16" thick, flat, bubbly pieces of molten something, opaqueish, whiteish, grayish glass like material. Either perlite, vermiculite, the light tan refractory cement, fiber reinforced concrete, ...I think that's all I used. Oh, and a little bit of sand. Thinking about a batch box version this time. And for sure bigger than 4". Oy.
