adobe+vermiculita insulation Other Oven Types Discuss adobe+vermiculita insulation in the Pizza Oven Design and Installation forums; So use lime on the dome render but not needed on the hearth insulation? Nope, no lime in vermiculite concrete. ...

[dmun]

So use lime on the dome render but not needed on the hearth insulation?

Nope, no lime in vermiculite concrete. The fluffy stuff substitutes for the solid aggregate in regular concrete.

And just as a side note, "render" is UK/Australian talk for stucco. No one will know what you're talking about here if you use that word. They'll think you're talking about purifying animal fats.

[david s]

For the dome I use a 10:1 vermiculite, cement mix. The less cement you use, the less dense the mixture becomes and consequently the better it will insulate. The trouble is that the cement is what holds it together. A 10:1 mix seems like it"ll never work when you apply it but it hardens up sufficiently to hold in place ok and provides a firm enough surface to stucco (render) onto. Others may disagree but this works for me.

[dmun]

For the dome I use a 10:1 vermiculite, cement mix.

The higher vermiculite proportion works fine if you premix the water and the portland with an electric drill paddle attachment: this slurry then wets the vermiculite and you get even distribution, which you can't be sure of with dry mixing.

[kebwi]

When you say it works fine, dmun, do you mean that if you use the described method (drill mix, then add vermiculite last) then up to 10:1 can replace the standard 5:1 even for structural support, like the hearth...or would you not recommend going over 5:1 for the hearth and only using higher ratios for the dome?

[dmun]

I can't say from personal experience since I used the 5:1 mix dry and add water method.
The leaner mix was developed after I built my oven. I'll let someone else who actually did it answer this question.

[cynon767]

I dry-mixed about 6.5 or 7 to 1 for the hearth insulation, and it worked fine. A little crumbly at the edges if I'm not careful with it, but otherwise totally solid (so far!).

[JoeyVelderrain]

if i use a blanket, and then the perlcrete, won't the perlcrete crush the blanket and flatten out making it useless?
and if i do use a blanket how do i attach it to my dome so it stays put whilst i coat the perlcrete on top of it?

[kebwi]

And to be precise, would an answer to JoeyVelderrain's question vary with the density of the blanket, 4#, 6#, 8#?

BTW, I had at least one manufacturer tell me that higher density insulation is more insulating than lower density, flying the face of the thermal conductivity data. I think he was just clueless though, right?

[papavino]

8# blanket is going to insulate better than 6# and 4#. The higher the density of fibers, the more little air pockets and tortuous the air path will be. It holds the heat back more efficiently than a less dense mesh of fibers.

As far as perlcrete crushing the blanket, I don't think I'd be too worried about it. I think the blankets will still insulate effectively with a little compression. The perlcrete mixture isn't that heavy.

[kebwi]

Ah, okay. In another thread there was some dancing around the issue of which is better, low density or higher.

Incidentally, why does this not jive with the thermal conductivities, which are lower for lower density blankets? My understanding is that lower thermal conductivity would imply lower transmission of heat, i.e., better insulation. I accept that the intuitive rationalization is incorrect, but I still don't understand the error in the logic.

Thanks.