John Moran : Yes, Both bricks and several kinds of rocks have been successfully applied to the outside of the drum! It is best left to a 2nd
Rocket Mass Heater R.M.H.Build,
or for a retro-fit onto an existing R.M.H., as would any attempt to '
Cob' more than 1/2 way up a barrel, always remembering that the total 'depth' of the Heat Riser
should
always be 3Xs the 'depth' of the
feed tube !
The reason that soapstone is often preferred and a premium is paid for soapstone, is that it expands with heat only slightly, and also contracts only a little while cooling !
Therefor it does not 'Creep'
enough to break a mechanical bond with what ever is used to make-up the outer shell of the R.M.H..Any failure here would result from the
amount of the expansion of the metal skin of the drums used on the outside of the R.M.H.! It is also slightly more than medium dense, and as such absorbs more heat,
and then radiates the heat out into its environment more efficiently than most other stone. It is for these combined characteristics that soapstone commands a premium
price on the open market !( It often 'looks' pretty too !)
Within the monolithic construction of the Thermal Mass Bench any common field stone will integrate well with the Cob, having said that there is a place that I travel to once
a week, that is generally up hill from my home and I generally can gather 20- 50 #s of rust red rocks of high Iron content which I transport home to add to a pile next to
my soft orange 'Common Brick' Pile! I am stock piling for future builds! I also have my Eye out for damaged/discarded Jo`tol type stoves with soapstone sides. Any soapstone,
or other rocks cleanly cleaved along fracture lines will be saved for Future facing stones ! I hope this helps and is timely, For the Good of the Craft, and all things Permies !
Think like Fire, Flow like a Gas, Don't be the Marshmallow! As always, your questions and comments are solicited and Welcome PYRO - Logically Big AL !
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