Hearth mass and insulation questions

[chickade]

I finished my base and now am working on my hearth. My oven will have the barrel vault design a I can't imagine how I would do the Pompeii brickwork.

I decided that I need more hearth mass than the Pompeii, since I have a farm and will be using the oven for multiple purposes, including bread and drying vegetables for storage.

However, I don't really want the massive oven that is used by the Alan Scott people, as I don't want to burn a fire for 3 hours before baking.

Since I am using Foamglas insulation, I'm thinking that I don't need a concrete hearth more than 2 inches thick to top the Foamglas for mass. Then I will do foil and 2 inches of concrete cladding over the vault (again, for mass), followed by 3 layers of the ceramic blanket.

I would very much appreciate your thoughts about the appropriateness of this hearth and insulation procedure for a farm oven. Thanks!

[Tscarborough]

Re: Hearth mass and insulation questions

Unless you fire it daily, you will be looking at a 5-6 hour firing at a bare minimum with that amount of cladding over the mass of the firebrick (unless the oven is tiny). Forget the tinfoil regardless, it serves no purpose other than forming a bond-breaker between the brick and the cladding.

The amount of mass needed is less than you may think, the insulation is much more important for an occasional use oven. With my small barrel vault (2.5"-3") and 2.5" floor hearth I can do 2 batches of bread the morning after a pizza bake, and still use it for another day to cook and 2 or 3 more days to dry.

[Laurentius]

Re: Hearth mass and insulation questions

You should'nt have a concrete hearth on top of your insulation! Its Slab, Insulation, Cooking floor (fire bricks, pizza stone, or something of this nature).

[chickade]

Re: Hearth mass and insulation questions

Is 2.5 inches of Foamglas layer under the firebricks enough? If not, what would you recommend?

Is 3 layers of ceramic fiber in addition to vermiculite in the housing OK for the vault?

Thanks in advance.

[Tscarborough]

Re: Hearth mass and insulation questions

If you build a house around the oven, drop the blanket and just use loose fill vermiculite. 2.5" of foamglass should be good

[chickade]

Re: Hearth mass and insulation questions

I appreciate your suggestions, and feel grateful that this forum is available for asking specific questions.

The oven I am building will be a relatively large one with inner dimensions of 36 x 48. Would that size decrease the need for additional mass in the hearth and vault given good insulation? The design calls for 300+ firebricks.