Aluminum Foil Over FB Blanket

[dottavio]

I am getting ready to insulate my oven and I wanted some feedback about the use of heady duty aluminum foil over the FB blanket.

I see this as having two purposes. First when I install my insulating perlite concrete it will be wet and fiber insulation normally does not work well when it is wet. Following that point I am going to have a dome enclosure. I am sure no matter how hard I try, over time the enclosure will crack. My thought is that the aluminum will protect the FB blanket, and bricks, from getting wet. (I have holes in my concrete hearth to let the water drip through if needed).

Of course it is best to not have any cracks, but I am planning for the work and hoping for the best.

Opinions????

Thanks

[REE REE B]

Hello
The FB blanket should not be covered with anything as it does a perfect job alone to insulate the oven. Your net step which would be your wire mesh and then stucco or whatever you wish to finish the oven off with. The FB blanket is a very solid insulation blanket and you should feel rest assured that it will do its job without worry. =-)
Thanks again and have fun!
Maria

[Amac]

I see this as having two purposes. First when I install my insulating perlite concrete it will be wet and fiber insulation normally does not work well when it is wet. Following that point I am going to have a dome enclosure. I am sure no matter how hard I try, over time the enclosure will crack. My thought is that the aluminum will protect the FB blanket, and bricks, from getting wet. (I have holes in my concrete hearth to let the water drip through if needed).

I wouldn't use the foil even if you do use a perlite layer. If you have an impermeable layer above the blanket it will work both ways and trap any moisture inside which would not be good.
The curing fires should take care of the moisture from the perlcrete

[Les]

From what I read you don't want to have aluminum in contact with concrete. It will corrode so you gain nothing. Best to just cover it and let it dry out.

[RTflorida]

Les is right. the foil will corrode in no time. There was an old wive's tale in oven building that said aluminum foil added a 'slip plane' that allows for movement between the layers, preventing cracking. The first negative to that is the confirmed chemical reation between any wet concrete product and foil, the foil will rot. The best insurance for minimizing cracking is to use fiber blanket for the insulation. the fact that it compresses allows for a bit of movement when the oven expands and contracts which helps lessen the cracking. Put the money that would be wasted on foil into a 12 pack , that should help ease you through the final stages of the build.

RT

[dottavio]

I did a quick google and infact the Army Corp of Engineers has banned the use of aluminum in concrete (although it is the calcium chloride that was the issue)

I did not know that there could be a an adverse chemical reaction. Gotta love the Forno Bravo forum.

Once again you all saved me a lot a work and heart ache.

I'm still deciding on one or two layers of FB blanket. Trying to save a few bucks by using pertile concrete. I know I'll need at least one inch to buffer the oven expansion from the hard outer dome shell

Thanks

Doug O

[Amac]

I used a few inches of vermicrete (virtually the same thing I guess). I didn't bother then with the metal lath (although I had bought some) because the vermicrete seemd like a more stable foundation for the stucco finish than anything I could manage with the lath. I have lit only a few fires since I did the dome cover but as yet no sign of cracking on that shell.
Good luck with it !