"....fired kiln, more porous bricks, commonly known as "kiln bricks" are a better choice. They are weaker, but they are much lighter, easier to form, and insulate far better than dense bricks. In any case, firebricks should not spall under rapid temperature change, and their strength should hold up well during rapid temperature changes."
What ever the terminology the porous bricks reflect heat the dense ones pass it through. Building shippable core that will pass the heat through itself and spall the concrete below it is far too specialized a piece of equipment for the average person. Also anything designed to accept such temps will result in disaster. Additionally putting dense bricks under the shippable core simply allows the heat through to the wood as that is what those type of brick were designed to do. IF the fire bricks were "popping" as was indicated in the videos then temps exceeding the bricks ratings were being achieved. This needs to be corrected or less educated individuals will end up causing themselves problems. This should have been posted in the shippable core section but I am not all that familiar with the posting tools.
H. K : Thank you for pointing out to other members the danger of using dense fire brick within the floor of a Combined Combustable Core Area!( Burn Tunnel-
Heat Riser )
As I said on another post, I think we are in complete agreement, Within my hierarchy of bricks the heavy, dense, and hard FireKiln Brick
is Only acceptable as a replacement for the weaker Lite fire Brick when used as the floor of the Feed tube or better yet the floor of the ash pit, and the planned
retention of Consolidated Fly Ash helps protect all of the Combined lower half of the combustion zone serving to increase Thermal shock protection\, overall re-
Fractility and insulate the entire feed tube !
Again that you for pointing out to our fellow members the danger of too much heat energy transference and not enough insulation under the Rocket Mass
Heaters Burner Section !
Success has a Thousand Fathers , Failure is an Orphan
LOOK AT THE " SIMILAR THREADS " BELOW !
Diego Footer on Permaculture Based Homesteads - from the Eat Your Dirt Summit