Advice on mortar over the dome

[MarkDLxu]

Hi All,
I’m about to finish all the bricks of the dome.

I want to fill all the gaps and cover the dome with some refractory mortar ... but how thick ?
( I will add then 3” ceramic fiber blanket and 3” perlicrete )

[MarkDLxu]

I maybe missed this paragraph on the Forno Bravo manual ...

Option: More Thermal Mass
You do not need to add thermal mass to your oven at this point, because the mass of the bricks and the mortar you have used to hold it together are more than sufficient for backyard pizza baking (or even restaurant pizza baking for that matter). If you plan on baking large volumes of bread, and want your oven to retain enough heat to bake multiple batches of bread from a single firing, you can add additional mass by applying 1/2”-2” of high heat mortar to the outside of the oven.

[david s]

If adding a thick layer over the dome in order to increase thermal mass, then that layer should contain burnout fibres or risk steam spalling.

[MarkDLxu]

Thanks David,
you mean to add a valve for steam that pass through this mortar layer?

[david s]

Not quite sure what you are asking for, but this may help. One litre of water expands to over 1500 litres of steam so allowing the layer to dry before applying fire is prudent. Generally one week drying for every inch of thickness is what potters use prior to slow heat increase to prevent steam spalling in sculptural clay work (no fibres). Drying is dependant on humidity, temperature and air movement, all quite variable.