It's unseasonably mild right now - about 12 C during the day and only 7-8 C at night. This is letting me get some masonry work done, albeit at night with the halogen light on. I've started on the oven entry, using engineering bricks. Much head scratching is going into this - I want the chimney to be supported on 4 lengths of angle iron (on the right side of the picture above). I want the oven dome to be completely separate from this masonry with a thermal break, which I'll probably make out of clay/sawdust mix or vermiculite. I reckon some of the ovens I've seen on the web leak a lot of heat up the chimney through the masonry joining the dome to the chimney, plus I'm worried about the thermal expansion of the dome cracking the masonry.
The plan is to have an arch at the front (on the right hand side above), with a span of angle iron and bricks behind it. Another span of angle iron and bricks will sit on the left hand side, above the entry to the oven dome. I'll fill all the gaps in the insulation mix afterwards. This plan may change - it's changed three times so far...Eventually all the messy masonry on the sides will be hidden by the cladding - the brick entry is set 2" forward from the insulation blocks to allow room for it. I still have no idea and no plan how to do this (render? more stones? pebbles?), but ignoring the problem is working fine for me at the moment.