Foil in the wall interior

[MK1]

David,
Thanks for the heads up. I agree that foil on the outside traps vapor in the vermiculite layer as your experience has shown. My thoughts are that a layer right on top of the firebrick, underneath the insufax and vermiculite would trap the moisture where it would help.
My guess is that alot of these ovens do have some moisture in the vermiculite, (not alot in dry climates). I suspect it cooks out a bit (with the vapor moving out the through the firebrick and entry arch) after the cooking is done leaving the oven in a fairly dry state until the next firing. Your situation is analogous (loosely) to a house that has been insulated with the vapor barrier to the outside rather than the inside.
Another observation is that the little building design has an advantage over a stuccoed igloo. More vapor would be trapped in the igloo, whereas the loose vermiculite poured over the masonry dome would transpire the vapor in a more efficient manner. I would love to have the two side by side and test.
I'm not sure I understand all of enz's post but from what I know lining the interior of the "house" with foil would be more moisture trapping with it's attendant insulation effectiveness loss that would outweigh any additional trapped radiation. From enz's post I would suppose a vapor barrier just above the masonry would be effective. Keep the insulation dry and all that.
With your build it might be advantageous to drill a 2" hole in the very top, just through to the vermiculite layer and install a small chimney with a cap to encourage a better drying out. If necessary maybe some small covered intake vents around the base at a ratio of 4 to 1 intake to exhaust which is considered the optimal ratio for a passive venting system, (not fan forced).


Mark

[dmun]

Foil has a massive surface area to volume ratio and aluminum is very reactive. Yes, a layer of oxide forms on aluminum to self protect, but with foil the entire sheet may turn to oxide.

The money quote from an earlier post: Thin reactive aluminum + corrosive portland = dust

[MK1]

dmun,
This is true and that's why I would use copper foil. Quite common as thruwall flashing for masons in the past. It's a little harder to source these days but it's out there. I love your build and have read every post associated with it. Did anything ever come out of the castable attempt besides a small explosion? I thought it looked promising with the exception of cost.
http://www.onlinemetals.com/merchant...=129&top_cat=0

Mark

[Neil2]

I put the foil between the brick dome and the vermiculite layer to act as a "slip" plane.

Why not ? It's cheap enough.

[david s]

Mark,
I have tried that technique of leaving a hole at the top and then filling it when all moisture has gone, but find it better to eliminate all moisture from the vermiculite layer before final render.

[MK1]

David,
My suggestion concerning the vent holes was to a builder that had placed his reflective foil in the wrong place, outside the insulation. It's the only remedy I can think of other than to remove his stucco cladding and then the foil. I do maintain that copper foil placed between the fire brick and the insulation would be beneficial. I don't know the cost/benefit ratio, but it would stop the spread of vapor from the oven interior into the insufax and vermiculite.

Mark