Some may be interested that I used
cob for my batch box
RMH bell. I have done a fair amount of home building using conventional materials, but I'll take cob over chemically treated plywood and vinyl siding any day! Cob is the most forgiving, natural building material I know of. I am also fond of curves, arches and anything other than right angles. After some challenges, I am very pleased with the performance of my cob Bell.
I decided to try building my
RMH bell around my metal slipper tub. Having worked with Cobb before, I was well aware of the challenge of Cobb shrinking and causing smoke leak problems, especially where it met the metal surface of the tub. Fire rated caulk has remedied this, but leaky cracks appeared in the cob, especially on some of the more complicated curves. When I first lit fires in the batch box, I kept a ready supply of fresh, damp cob mix for filling cracks. These fixes worked, but new leaks kept showing up in other areas. I spotted them quickly and stopped the smoke before the smoke stopped me. These cracks in the cob are not surprising knowing that cob is not good at shrinking and expansion due to the heat of the stove. My RMH is in my
greenhouse so the smoke is easily cleared in the smaller 12x12 structure. I am noticing fewer leaks as the heat hardens the cob. I am confident the leaking will go away completely.
My most expensive piece for my RMH is the 2x2 ft plate steel I use for the ceiling of my bell. I also don't seem to have cracks or problems with my one inch fire brick, the next expensive part of my stove. The rest of the stove was free, thanks to a large pile of subsoil I could use for making cob. Being from Alaska originally, I am used to working with gaskets around metal
wood stove doors, so I was ambitious about using a gasket between the top of my cob Bell and the 2x2 plate steel. I wanted to be able to lift up the 2x2 plate steel and examine the condition of the fire brick and other potential concerns within the innards of the RMH. This means having to replace the fire rated caulk whenever I lift the plate metal and do an inspection. I've been able to cook and heat
water for the bath on the plate metal surface so this is made having to replace the caulk worthwhile. Thanks to a Permies's post, the batch box door and inspection port door are simply lids from Pyrex dishes. I am in Central North Carolina if anyone is interested in seeing my RMH.