metal frame advice ( jamie olivers oven)

[pizza683]

hello , hoping someone has some advice on this, i am mid build on a jamie oliver replica oven , as you know the chimney on jamies oven exits through the middle centre of the oven for aesthetics i have a mill stone wheel of 102kg and twisted brickwork chimney and top out stones to support . i have had a steel frame made that will support this , i am slightley concerned about the expansion of the steel ? to counter any cracking of the finished render ( slightly different finish to jamies) i was going to wrap this entire metal frame in insulation blanket or thin insulation boards prior to building up the outer dome with a vermiculite inner and eventually a normal sand and cement render with pigment added with reinforcement fibres ,this will of course encapsulate inner done and the metal frame , hoping someone has done something along the same lines

ps: take no notice of the brick packers under the metal frame in the picture as i have yet to weld another section on to get it to the correct height