Vapor Barrier under the FB

[Tim_FB]

I was referring to Ceramic Fire Board. I am using 6 inches which I know might be over kill. I had concern over using plastic bc the stuff which you mentioned. I am also gonna have 4 and 1/2 inch floor FB turned on its side.

Thanks

Fiber Insulation Board would go concrete hearth (vermiculite not required) then Fiber Board. As Gulf mentioned we don't use a vapor barrier. We prefer the insulation be directly on the hearth, sand to level and use for heat conductivity then the cooking floor.

If you are going for a 4.5" floor / dome, It would be comparable to our and Modena oven. 2.5" floor with 4" dome. On that oven, we use 4" of floor insulation, 4" around the side dome and 6" above the dome. This allows the oven to be at about 600 degrees the next day after a pizzeria shuts their oven down.

The additional insulation on the floor will support more thermal mass, so you can easily over heat the oven. If you are doing prolonged bread baking, etc, your floor will have much more throughput the way you are approaching it. But if you intend to serve small groups or only a couple batches of bread, it is overkill.

Tim

[UtahBeehiver]

What is the ultimate cooking goal of the oven? Nothing wrong with turning bricks on 4.5" side if you are in need of good thermal mass for baking breads. For normal pizzas and roasting laying the fire brick flat (2.5") is sufficient especially with so much floor insulation. The more thermal mass the more fuel you will need to bring the oven to temperature There will be an nominal increase of cost for the bricks and additional joints but neither of these are deal killers. Ultimately it is how you will use the oven.

[RugerFan777]

I was referring to Ceramic Fire Board. I am using 6 inches which I know might be over kill. I had concern over using plastic bc the stuff which you mentioned. I am also gonna have 4 and 1/2 inch floor FB turned on its side.

Thanks

[Gulf]

Rugerfan777,

Welcome to the forum.

In this case, I don't want to assume that I know to what "FB" is referring. Forno Bravo (oven)? Fire Brick? Forno Bravo does not have a recommendation for including a moisture barrier in their installation instructions. It is just one of the options that has been recommended by some independant oven builders on this forum.

A vapor barrier, if used, should be between the hearth slab and the insulating layer. A vapor barrier can be made from any of the plastic films that are in the hardware/building supply stores. They can usually be found near the concrete products. Other materials that will work just as well could be masonry waterproofing paint, a remnant of vynil floor covering, a piece of old swimming pool/pond liner, etc. I would definately use one if the oven will have a v/pecrete floor insulation layer or multiple layers of board insulation. However, I would like to include this warning. A discussion a little while back brought out a concern that one layer of board insulation could leave a splice where heat could possibly get down to the plastic film. Splices on multiple layers of board insulation can be staggered to prevent that from happening.

Elevating the insulation from the hearth slab is another option that will limit or even prevent wicking.

I hope this helps.

[RugerFan777]

I have done a search and can't find what is the best thing to use under the FB?

Thanks