I've been thinking about similar things and wondering about materials for Core 3.0/4.0/whatever version we're up to. I wrote about the possibility of a hybrid core, making the inner liner out of split fire bricks for strength and durability and packing in 8:1 perlite/clay insulation around them to hold them in place and super insulate the center of the core. If this Kast-o-lite stuff is as impressive as they claim, an inner core liner made of refractory cement wrapped in high insulation perlite clay could be an amazing combo. A buddy of mine tried something like this, he poured a core but "painted" a bunch of refractory cement on the wood inner form then packed something like 15:1 perlite/clay around it. He said his crumbled and broke, which makes sense, it was way too thin.
I used dimensions from Christine Baker's thread back a bit ago on a 6" core to estimate volume of material needed (5.3" wide, 24" long, and I made this shorter, 7.3" tall), for a 1" liner, it would be 1 bag of cement, for a 2" liner, it would be around 3 bags. Since it's super hard and it will be surrounded in insulation, maybe the 1" liner would be enough? Use the standard strategy for pouring a core, make an outer box and an inner form, but I'd make the feed tube and heat riser tubes tall (6" above the top of the burn tunnel). When you pour the core, you could still only put 1" of refractory cement around the inner form, let it dry, then take off the outer box, build a second outer box for the final size of the core + insulation, pack in the insulating mix (8:1 perlite/clay), set the dry core liner into the box and pack insulating perlite/clay around it all the way to to top of the outer box, covering the previously uncovered parts of the feed tube and riser tube. I lined my feed tube with split fire brick so I wouldn't have any problems with crumbling material, something like that could work, or maybe you try to paint on a thicker coat of refractory cement onto the upper parts of the feed tube and riser tube, then pack the insulating mix around it and hope that's enough?
So, the question is, would this be enough of an improvement to make it worth the extra effort? The 3000 degree rating sounds impressive, the hardness would be great, the low heat conductivity combined with surrounding it with a high insulating wrap means it should direct way more heat back into the fire than your typical fire brick build and even more than a 1:1 perlite/clay mix cast core.
You ready to go build one?
You've got me curious, I'm just out of places where I need a core. And while I'm loving the experimentation and design thinking, my core works really well and I'm not sure how much it would improve what I've got. If I didn't have a heater and I was getting ready to build one, I think I'd go for the extra effort and do the refractory liner.
Have you worked with the material at all before? I was surprised how heavy and awful to work with the 1:1 perlite/clay mix was, I wonder what the refractory cement is like to work with around forms and packing in and the like ...