Vermiculite Concrete hearth insulation Pompeii Oven Construction Discuss Vermiculite Concrete hearth insulation in the Pizza Oven Design and Installation forums; I’m going to pour my vermiculite concrete layer this weekend. I poured test sample of the vermiculite and noticed areas ...

[jrparks]

I’m going to pour my vermiculite concrete layer this weekend. I poured test sample of the vermiculite and noticed areas of small air pockets. Should I be concerned with moisture or air pocket in the bottom insulation layer that may expand later when heat is applied? Perhaps it is assumed that hot air and steam slowly works its way out thru the brick floor and is not a problem.
Cheers,

[dmun]

Air pockets are the point of vermiculite concrete. It's the air trapped in the layer that insulates. You're good to go.

[Breven]

Exactly...the air pockets are your friend. However, I would pat the wet mixture down lightly when you pour it and level it...tiny airpockets is the idea, big caves of air probably not so great.

[egalecki]

Something I noticed when I was stuccoing my oven- in the front, where my vermicrete had slumped a little and was a tad thick, I took a brick and "sanded" it a little to get it flat. I noticed that the newly exposed inside was much softer and crumblier than the outside. Sort of like when you make a sand castle and it dries on the outside, and when you mess with it, it all slides out. When I applied the vermicrete to the exterior of the landing and vent, I patted it into position. Did this bring the portland to the surface more, sort of making a shell around the vermiculite?

I just covered the spot up with stucco as I had intended, but if I hadn't meant to do that, I would have had a problem, since it was a vertical surface. If it had been a horizontal one, I don't think it would have mattered. I have the same vermicrete under the oven and the insulating board, and it's never shifted or compacted in any way. But I didn't apply it the same way, either. It was mixed and dumped into the form, screeded flat, and left alone.

Just wondering if the way you apply the vermicrete changes the insulating value and/or the structural integrity. Obviously, the layer around the oven doesn't need the same strength as the layer under it.

[jrparks]

Thanks for the input. I will pour my vermiculite with confidence and my pizza will taste great.
I have posted a picture of my test pour (broken to see the inside). It is a very interesting medium to work with. Also, I found that mixing the dry vermiculite & cement, (5:1 ratio, each part being 2.5 quarts) in a 5 gallon bucket with lid works well. Tumble for a few minutes then I am then transferring it into other buckets until I have enough to mix with water and fill my form.
Cheers,
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