Using Clay Flue Liner for Burn Tunnel & Heat Riser?

Big Al,
From Wikipedia:
"....fired kiln, more porous bricks, commonly known as "kiln bricks" are a better choice.[1] 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 in a lay persons hands. 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. That is what most ceramics are 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

Harry Kaneer : Thank you for your comment about the increased danger of using Dense fire brick within the Combined Combustion area of the Rocket
Burner, and specifically the floor of the Burn Tunnel !

I Think we are in total agreement, My hierarchy of bricks places Dense fire brick at the bottom when constructing the combined combustion chamber
( Burn Tunnel and Heat Riser ! ) By selecting a hypothetical use of hard, Dense, FireKiln Brick for part of the floor of the ash pit- In a
build where I am determined to leave a Consolidated Layer of Fly Ash as an additional layer of protection of the area surrounding the Feed Tube, AND the
floor of the Burn Tunnel, I am greatly improving the longevity of the entire Combustion zone and replacing weak fairure-prone lite fire bricks at a specific
area where I can compensate for the additional heat transference by retainng more fly ash both with-in the Ash Pit and the Foor of the Burn Tunnel.

It is still a primary responsibility of the RMH builder to make sure that the Floor of the housing structure does not suffer damage from the heat energy
radiated from the Mass of the Rocket Burner or the initial 4-5 feet of the Thermal Mass! Again thank you for pointing out the need for me to clarify that point ! Big AL!

There are some long skinny thermometers that could be installed against the wood flooring beneath the burn floor. A couple long hot burns could determine whether it's a concern. Al, any thoughts on the maximum allowable temperature ?

I wonder if some ash were mixed with fire clay, could a suitably insulated and durable clinker be formed on the brick burn floor ?

Dale : I hunted for a RMHs in green house post where a RMH was built with decent insulation over old Sun bleached decking and sustained a fire, right now the
Forum Thread is lost, however, unless the Rocket Burner base was well insulated with 3'' compressed perlite below the burn tunnel, or the base was designed
to spread heat into the ground as a additional Thermal Mass ,allowable temps should be in the range of 451dF ! Big AL !

I don't know where my head was at here, 451dF is famously the ignition point for paper , 300dF with excursions to 400dF had ought to be safe, and over Concrete
500dF if you were trying to make the floor part of your thermal mass ! Other wise cooler will never be wrong ! Big AL