Just a question regarding my idea of putting an extra layer of bricks below the dome, would this also create a insulating factor? Or does it need special material as heart insulator?
I am asking just to understand if I could fix the grout and heart insulation problem with this idea.
I feel similar to Tscar that this oven doesn't seem to have insulation under the floor. If that is the case, then you need not worry about the mortar joints.
If you buy this oven, then one solution would be to remove the existing mortared floor brick, insulate with perlite/concrete, ceramic or mineral wool board then use low duty firebrick splits (usually 4"x9"x1.25").....this is all based on the assumption you can remove enough material to add insulation in the first place.