Vermiculite with no blanket

[Rslt]

Hi, hope I don't get a collective groan but have searched and not found an answer.
Can I skip using ceramic blanket and apply only vermiculite as an insulator on the exterior of the dome?
Thanks in advance

[MarkJerling]

Yes you can, but vermiculite cement is a much poorer insulator than the blanket. Of course, if you built a "house" for the dome, there's nothing stopping you filling the resulting cavity with vermiculite. That will work well, but vermiculite cement is a poor insulator.

[Rslt]

Ok, thank you, appreciate it.

[Petter]

Has anyone seen or experienced any cracking in the outer render as a result of not having the blanket as expansion joint between the dome and perlite/vermiculite concrete?

[MarkJerling]

Has anyone seen or experienced any cracking in the outer render as a result of not having the blanket as expansion joint between the dome and perlite/vermiculite concrete?

Yes, two friends of mine built such an oven and the outer render has cracked badly.

[Petter]

Great info, Thanks a lot!

[Chops]

What Grade of Vermiculite should you use When applying to your Dome & Floor areas ?

[david s]

Yes I’ve cracked the outer shell of an oven that had no blanket. The problem is that a very thick vermicrete layerwill still have a lot of moisture deeper in and particularly where it contacts the inner dense dome.If this suddenly turns to steam you’re in trouble. I simply rendered another layer over the cracked outer shell after several more drying fires to drive out the moisture. After that experience I began doing layers of vermicrete no thicker than an inch and a half thick, with a week of drying before adding a subsequent layer. When the safer blanket became cheaper I started using it instead of a vermicrete only insulation layer.

Any grade of perlite or vermiculite will work, but the finer grade requires more water and as it is a problem to remove, it’s not a great choice. The coarse grade doesn’t hold together so well, particularly with the leaner mixes. I compromise and use a medium grade.