If you blend your vermiculite with cement and fill a 20 gallons space, it will weigh well over 300 pounds. Add in the drum plus
firewood and those vogelzang legs might not bear the weight. Consider additional support. Bear in mind that even thermal
concrete will expand as it heats. More heat, more expansion, and your objective is higher heat. This expansion is in all directions, inward, outward, and axial.
To account for thermal expansion, consider packing the vermiculite or perlite without a cement/mortar/bonding agent. This would allow the material to compress, absorbing the expansion rather than deforming both of the drums.
The Vogelzang drum kit is about as simple as can be. Bear in mind that the flames will eventually corrode the drums, particularly the bottom (coals) and top (flame) of the combustion drum, and the flue pipe. If the drum is oxygen poor (slow burn), the steel in the drum would produce more magnetite. This will fall apart in flakes, but can hold itself up to some degree. If oxygen rich (fast fire), the steel in the drum would produce more iron oxide (rust). The rust is a much faster form of corrosion. The combustion chamber can be lined with fire brick to protect the drum. Standing the drum on end will make it easy to install the brick. They gotta be tight. You can mortar these in place. Another option is a castable mortar. This can be packed by hand to line the drum.
This stuff would work, 50# would line that drum.
Rules:
-If you can make a mud pie, you can use this stuff.
-Use as little
water as possible
-It has to be dry/dryer/driest before your first burn, you can dry it with a couple of
light bulbs left on for a few days
-When you start packing it in, you cant stop until you are done.
-you WILL wear a N95 dust mask while using this stuff
-After repeated cycles of heating and cooling, this stuff will present thermal fracturing-cracks. As long as the pieces are snug together against the shell, they will support themselves.
