Solid base to build on. It ends up very heavy!
I used concrete blocks and then made a steel frame and poured a concrete pad on top.
In the middle area where the base of the oven will be I a poured a concrete/vermiculite base about 30mm thick to act as insulation for the stone.
next step is to create the chamber
Step 1: The chamber
For this I used Blue engineering bricks, type A are the only ones good for this sort of heat, you don't need firebricks (they cost lots)
I used about 200 bricks, got them for about £60 off ebay
the mortar needs to be high temp, so a mix using terracotta clay sand and cement was used, it goes off but gets harder when fired.
as you can see i created a form using hardboard and ply. I bought the clay from a kiln/pottery suppliers. It needs to be high temp firing.
As you can see from the second 2 photos I have created the chamber then used regular bricks backed by firebricks to make the opening on the front, I used a form for this brickwork as well.
There is a special dimension for the opening, The height of the opening needs to be no more then about 70% of the height of the chamber otherwise smoke comes out and it needs to be wide enough to allow good access.
Step 2: The surround
For this I built a regular mini brick wall about 40mm away at the base around the chamber.
once complete the void created was filled with 4 large bags of vermiculite grains
This is important as you want the heat to stay in the oven not leak out.
I wanted the oven to look like a little house so used some old timber to make a roof frame
the clad that in OSB, battens and tiled it. I had the dragon laying around for 5 years, finally a use for it!
use anything you can find, I used bits of tile, old terracotta bits and bricks found around the place.
Step 3: Stone work and testing
Inside the slabs are not stuck, just laid so they can be replaced when burnt out
I left an overhang at the front and sides and there is enough room to pull the pizza out spin it and put back in
I finished the front of the roof bits of wood lurking round the place
I left the ridge tiles loose so could top up the vermiculite.
Put a flue on and fired it up
check the results pretty good :)
Step 4: Learnings
Fixed by moving the timbers at last 6" away from the flue
The flue started as a 4" pipe, this was too small, then used ceramic flue liners, these have all cracked.
so next I will replace it with stainless twin wall flue when I can get some.
where you make any frame for a form, make sure it comes apart and drops away from the arch otherwise you will have to get the big hammer out!
lastly make it as big as you can fit even though mine is big its still only really good for about 2 or 3 large pizzas at a time
ping me a msg if you have questions
Enjoy your al-fresco dining with friends.
Oh the greenhouse has the same 12v dc lighting system as my house, all solar, see my other Instructable
Have fun ... Rob