New & concrete?

I haven't been keeping up with the RMH world since Ernie & Erica W. were promoting them so heavily more than ten years ago. Is their basic RMH model (which they so generously gave away their plans for) still state-of-the-art or are there innovations in RMH design that have there been generally accepted?

Also, doesn't Earthship founder Michael Reynolds write that cob and concrete have almost similar insulating properties? Are people building RMHs out of concrete in place of cob?

The advantage of cob instead of concrete is multifold;
- often on site.
- therefore has reduced cash expenditure
- but more physical work.
- cob is easier to mold
- cob can easily be broken and removed if need be.

3 things that come to mind :

- Building a brick heat riser then wrapping it with superwool can be replaced with a 5 minute riser.

- Using pipe in the mass can be replaced with a bell or stratification chamber

- Many people have switched from a J tube to a batch box design for its longer burn time and being able to see the fire

A Wisner design will still work just fine, its just a matter of what your goals are and sometimes what you have available to use.

Welcome to the forum!

In this thread Top-Questions-Rocket-Mass-Heaters

This is what it says about "Materials and Methods"

Erica says, "different mixes for different areas:
thermal cob, straw-cob (structural cob), perlite-cob, clay slip, clay-sand mortar, refractories, insulation
Paul's "cobbish" perlite-clay with added fiber, shippable core

Erica says, "mass coatings (finishes) - Primer on cob plasters - or you can build a masonry box as a one-step outer surface and infill with mortar/cob/dirt around the pipes - or you can build a hardee-backer box (and plaster or tile it if you like). Matt Walker's been doing some unconventional finishes for his lower-mass outdoor benches, e.g. cast-cement tops and cement-board sides: Multifunction-outdoor-rocket-system

https://permies.com/t/41635/Top-Questions-Rocket-Mass-Heaters

This is the newer FAQ that you or others might enjoy:

https://permies.com/t/191801/Building-Ultimate-Rocket-Mass-Heater

Something to ponder..

https://ceramics.org/ceramic-tech-today/ceramic-video/video-the-physics-of-exploding-concrete