Hearth Slab Flashing

[El Puaco]

A question about the hearth flashing. The directions call for aluminum flashing. My experience with construction is that aluminum is generally not used with concrete pours because the chemicals in concrete eat up the aluminum. My thinking is that since all we are trying to do is to isolate the hearth from the stand that maybe a sacrificial barrier may be just fine. On the other hand if the idea is to give an actual slip plane maybe we should use a stainless steel flashing (which would be a lot more expensive) or galvanized steel. Either of these would probably hold up a lot better than aluminum. Any insights?

[dmun]

flashing

it's been debated whether the flashing does any good or not. Why not just use tarpaper? It's cheap, chemically stable, and available from any roofing supply.

[james]

I don't think the flashing is necessary. The idea was that it would serve as a slip plane between thermal layers moving at different rates, but what you see is that the interfaces between structural concrete and the concrete block and between the structural concrete and the vermiculite concrete don't get hot -- so the slip plane isn't necessary.

We do not include that step in the Forno Bravo oven installation guides.

James

[El Puaco]

Hearth

Thanks James. I wonder if I should have left the rebar in the concrete block cells long enough to tie into the bottom of the hearth. In any case I will need to deal with the cells that I didn't dowel into the slab and fill with concrete. They would hold 12-15 60# bags of concrete. Maybe the flashing would be an answer to this or possibly the roofing paper that dmun mentioned.

[james]

I think these are two separate functions. Tieing the hearth and the stand together with rebar through both components is a nice idea, particularly in earthquake prone areas. That said, I live in California and did not do that on my ovens here. Still, if you can do it easily, it would add structural integrity.

The flashing between layers is the "thermal" slip plane (originally included to allow for smooth thermal expansion and contraction), not a structural component.

For the stand, my thought it to keep it simple (and well insulated).

James

[El Puaco]

James,

I agree completely. My only (minor) problem is to deal with the cells that I didn't fill when I was doing the "every other one" business and filling them with concrete. Those empty cells are going to eat a few bags of concrete unless I find a way to plug them.

I read a few months back that you would sell a vent for one of the Casa ovens. Is that offer still good?

[james]

You can crumble up the concrete bags and stuff them into the open stand cores, and they will block the concrete for pouring in. It works.

Yes, we are going to add the Casa vent to our online store to make it easier to assemble the vent area -- it sure beats spending hours cutting bricks, plus the opening is already round and fits the DuraTech anchor plate and chimney pieces.

If you need it soon, drop me an email (james@fornobravo.com).

James