Two steps forward, one step back. After adding 200-300kg more weight, I decided to consult Captain Courageous, and after much discussion came to the conclusion that there was no way that the deck would hold close to 400kg.
I have now stripped all the brick paving as well as the sand underlay and with the help of Brat Deluxe (Coitus Interruptus) moved the base to another (hopefully stronger) deck. Then I relaid the bricks, built the door frame and moulded the sand form that defines the inner volume of the oven. As mentioned in my last post the door height must be 63% of the inner dome height. Another important measurement is the ratio of dome height to base diameter. This should be between 60 and 75%. Here are my final figures.
Door Height = 300mm
Dome Height = 476mm
Ratio = 63%
Base Diameter = 795mm
Ratio = 60%
This should work. Here are some images of the project as it stands now.
I built a little timber deck for the top of the door frame to rest on while I cemented it in.
Here is what it looks like cemented with the inner sand form in the background.
This is what the sand form looks like. This now gets covered with wet newspapers and the first (inner) layer of clay mix gets plastered over it (hopefully tomorrow).
Enough for now.