Jack Pent : While your sketch was a little hard to follow, most of us are used to answering these questions, and if we don't Think we understand -we will ask!
Even if this is Rocket Science

-All the Science/Math you learned by the 4th grade. Mostly its the vocabulary that Ianto Evans who is a man of Welsh
Extraction, created to give us a common framework -within which to work. ( some times I think I can hear him Laughing !)
Good news on the 'Fire' Bricks, there have been literally 10s of thousands of early Rocket Mass Heaters made from old dead-soft housing bricks commonly
used in housing construction 100 years ago and easy to find for less than $1 apiece or free on Craigs list! Many of these Rockets were made 20 years ago
and still have their original bricks and Barrel !
I can recommend a second site that mostly deals with kilns for Pottery / Ceramics and so called earth /clay ovens like you get the best pizzas cooked in!
O. K. , please Goto :
" www.traditionaloven.com ''
You are looking for the previous articles section where you will find articles on what is
'fire clay' and articles on
fire bricks and
Alternatives to fire bricks
As the article explains -there are two types of 'Fire brick' 1) soft and light 2) Hard and dense And each has a separate purpose- I am telling you now
that we generally prefer the dense fire buck weighing 8 lbs +- !
The old, dead-soft, red, clay bricks (you can use them like sidewalk chalk and they leave a well defined mark behind themselves ) fall nicely between the
two extremes in 'fire brick'
Unfortunately the ratio you chose will not make a good 'snow ball' it will just not hold together in your hand. By time time you have used enough Clay to
Perlight to end up with a rigid enough structure that can last even one heating season, we lose some of the insulate qualities of the perlite and need between
2'' and 3'' thickness
Have you seen the large diameter tubes of heavy cardboard usually called Sonotubes that are used as forms to make in-ground supporting piers for
general construction ? you can easily use a 8'' Sonotube as the inside form of your Heat Riser, and regular stovepipe for the outside wall of your Heat Riser,
The Sonotube will burn up burn out during the 1st few initial firing of your future Rocket Mass Heater RMH!
One more thing, We try hard to listen to every single new idea -as that is the only way we will ever grow and improve ! In spite of that we can fall into the
habit of ''this is the way we have always done it''! If you do not like or understand an answer you get here always feel free to ask for a second opinion !
For the Good of the Craft!
Think like Fire! Flow like a Gas! don't be the Marshmallow! As always, your comments and questions are solicited and Welcome Big AL