In order for the oven to work properly it needs a thick layer of insulation and in order to hold this insulation in the oven needs an exterior wall. It can be built from 4" concrete block but by building a steel stud wall with an exterior sheathing of concrete board (like drywall made of concrete) you end up with an extra 4 inches of insulation.
Steel studs are flimsy things until they all get tied together and sheathed with drywall (or concrete board). They are sort of a bitch to work with. i think I prefer wood although steel studs may be "the future of the industry."
In the front I made a little slot to put the temperature readout meter. I also had to build the face up square in order to meet the steel stud walls flush. I also spent this time corbelling the chimney back and in due time I will mortar on a 8" insulated flue pipe which will take the chimney through the roof of the shed that will cover the oven and the adjacent rooms.
The next step was to fill all that space with vermiculite. Vermiculite is a mineral that, when heated, will expand into little puffy worm shaped rice krispie looking things (worms=verm-). It is used most commonly to condition soils. It loosens up heavy clay soils and retains water in sandy soils. Becuase it is so light weight it also makes a great loose fill insulation and is fireproof and so can get hot where it touches the oven cladding without burning up. At first I though 20 bags would do the trick but I ended up needing 5 more and at $18 a bag this was not so cheap.
So now on to the baking!
Mental Floss has abducted me
9 years ago