Indoor oven on a gym ball

[crolande]

So, the dome has been cast and now it's time to move on to the heart. I've seen a couple of pictures on this forum where the placement of the dome is on top of firebrick. Is that a common placement model? This means that the outermost bricks are locked by the dome, which ought actually be loose in order to be able to move due to the heat. I further assume that the firebricks are placed on top of the CaSi slab. Fine sand is placed underneath and bricks are laid loosely.

Right?

[fox]

Some folk fit the bricks inside the dome in which case you need to cut them super accurate and leave an expansion gap all around, other folk much prefer to fit the dome on top of the bricks so the bricks are then much easier to cut and they are able to move regardless of the domes weight.
Personally I try to avoid using sand to bed the bricks as it is oh so easy to move the sand while placing the bricks and cause more issues, all the ceramic fibre board I have used is very flat and there is no need for sand!

[crolande]

Questions, questions questions!!

Since I have to move my casting to the final location, I have reduced the thickness of the first cast slightly. This is to minimize the weight. So placed in its final position, I thought I would cast on another 2.5 centimeters of home brew. How should I treat the first cast to get good adhesion second round? Can I use primer for concrete or will that endanger the operation of the oven?