Exterior Oven Shell: Stucco, Mortar or Left-Over High-Temperature Mortar?

Just finished laying the fire brick today and can’t wait to get morning on the next step. The directions mention that the shell coat can either be stucco or mortar. I have a good amount of high temp mortar mix left and was wondering if there is any reason I shouldn’t use it over the ceramic fiber blanket & chicken wire.

If your high-temperature mortar is made from our recommended blend of (4) materials (Silica / Pool Filter Sand, Fireclay, Portland Cement & Lime) - then you are fine.

But if your high-temperature mortar is from a refractory manufacturer (HeatStop 50, Mortar Mix 413, Sairset or Sairbond)… then NO. These high-end refractories BEGIN curing when they hit 800°. Sure, the high-temp mortars in a bag / dry will get hard… they won’t reach their full strength until they are cured (again, starting at 800°).

Thinking about using wet / pre-mix mortar? EVEN WORSE! Those refractories will stay soft / puddy-like until fired… and the outside of your oven will look like a back-side of a Florida alligator once it’s dry.

Stucco is preferred…

Mortar is runner-up.

Thanks!! I actually was using Heat Stop because I had a hard time getting fire clay near me to make my own mix!! I’ll find stucco or use mortar if I can’t.