Can anyone tell me any best practices when mortaring the bricks around the oven shell? How thick do you make the thin joints between the firebricks? Should I use spacers?
Are you speaking of the Stucco shell that goes over the blanket & chicken wire?
If so, you want that mortar to be thin - about 1/8".
But I wouldn’t apply a firebrick on the outside (if it is the stucco shell you are speaking of).
You want to use a thin brick veneer. Placing a firebrick on the outside of the blanket is not correct.
The oven should look like this (from the inside-to-outside).
Foam oven form. Firebrick. 2 Layers of blanket. Chicken Wire. 2 layers of Stucco. Thin layer of mortar w/ brick veneer attached.