Do I Need High-Temp Mortar For The Stucco Layers?

Is the high temp mixture required for the stucco layers as well as the brick?

Good question, Dave. The answer is emphatically “No.” Think of your oven build as having a hot (fire) zone, and a cold zone. The stucco is outside the hot zone envelope.

You can use inexpensive Type “S” (for “standard,” not “stucco”—fun fact!) mortar for your stucco. It sets up in a few days to a hard protective shell that will keep your mineral fiber insulation fluffed up and shielded from grandkids and heavy birds.

The base under the stucco on most builds is the standard-brick hearth frame (not yours, because you are constructing a monolithic poured slab). That frame does need the high temp mortar because it sits in a “twilight” zone that straddles the hot hearth and arch, and the outside cold environment.

Great, Thanks…I will be installing a double wrap of the ceramic blanket and I believe it calls for two layers of the Stucco/Type S mortar after that?


Spot-on, Dave. Remembering, of course, that after the blanket comes the metal lathe wrapping, a.k.a. chicken wire. I know you won’t be skipping that crucial step! :slight_smile:

Correct, thanks Matt.
Have a great weekend!

Is Portland cement okay to use for the stucco layer. I have 2 unopened bags.


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Portland cement by itself would be too hard and crack over time. I did a little research on mortars early on in my project that you can find here:

Mortar Investigation

Since I posted that I’ve mixed all the mortar for my veneer using leftover Portland Cement and Lime. I needed to buy a lot more sand though.

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Ken is absolutely correct.

If you have left-over Portland cement and want to use it up, save it for the veneer as Ken did. He does point out that you’ll need other materials to make it a flexible and strong mix.

For the stucco layer I’d prefer the ready-mix as suggested upthread. The Lowes in Milford and Newington both claim they have Sakrete Type S in stock.