connecting inner and outer arches

[maineoven]

Ok, I've tried to find this explained in the archived threads but still not sure I understand. I have an inner arch that is made of firebrick and is basically fused into my dome. Actually it protrudes about 4 inches from the dome. I am going to build the outer arch of red brick and have it maybe a half inch wider than the inner arch all around.
I have read that you should mortar the bottom bricks of the outer arch to the floor. I don't understand if I should be motoring the bricks of the outer arch to the bricks of the inner arch. I read about a gap to prevent heat loss and also if the arches are mortared together the joints will break from heat differentials. So could I just have the outer arch bricks bump up against the inner firebricks and just not mortar them together?
If I do this I just don't understand what keeps the outer arch from flopping over, except the bond of the chimney over the created vent.

[Les]

Re: connecting inner and outer arches

I don't understand if I should be motoring the bricks of the outer arch to the bricks of the inner arch. I read about a gap to prevent heat loss and also if the arches are mortared together the joints will break from heat differentials..

Yes, use mortar. Once you get outside the dome the heat loss is insignificant. There has been much discussion about a "heat break". I can cook for three days after one fire. If someone can use the oven after four (our design), I am not aware of it.