Spongy Vermiculite Hearth - solution thermally sound?

[Petrizzi]

Hi All,

Great forum BTW!

I'm in the middle of a Casa90 installation, just poured the hearth last weekend. I used a barrel mixer for both the structural and thermal layers. Of course it was only after that I realized the vermiculite/portland 5:1 mixture would have been better mixed by hand in a wheelbarrow. Since I mixed it in the mixer, it was very soupy an uneven. I had to add a lot of water to get it to 'pour' out of the barrel and as a result the portland/water part went straight to the bottom with vermiculite floating everywhere. What a mess!

My fear is the same thing happened after pouring this soupy mix on the structural layer. After all was done curing, the thermal layer remained rather loose and spongy on top even pieces of vermiculite could be easily picked off. I could also push it down with my finger a bit (not far but enough to alarm me) and grew concerned that the weight of the oven would do the same, making for an unstable, difficult to control flooring.

So in effort to secure this surface I mixed straight portland cement with water and dabbed it all about atop the vermiculite surface. This worked in that the top is now more solid and pieces cannot be picked off. More importantly, I am more comfortable with the idea of adding the weight of the oven parts. But there is also now a thin layer of portland (~1/8") all about.

Q: Is this thin layer of portland atop the vermiculite going to cause undesirable thermal characteristics in the cooking floor?

Best regards!

[asudavew]

Picasa Web Albums - Dwats - Oven Mission ...

The link above shows how I covered my insulating layer.
I poured about 3/4's of an inch of high temp mortar over the top.

I haven't finished my oven yet, but the consensus was that it would be fine.

So I imagine you will be just fine too!

Don't forget to post some pics!

[james]

Ciao Petrizzi,

I agree with David. This is pretty normal and your hearth will be just fine. Keep going. Vermiculite is pretty odd stuff, but it will definitely work.
James

[Petrizzi]

Hi guys,

Thanks for your comments. Glad to hear I don't need tear anything apart and start over I am one of those engineer types that if things deviate in the slightest from the instructions, I freak out a bit. This was one of those moments.

See the following link for pictures of my project
Hmm, cannot post a link yet. Just a sec.

Cheers!

[Petrizzi]

Now that my post count is >=2 ...

ATmega32's slideshow on Flickr

[james]

Excellent work. You look very under control. :-) Sorry about the post count, but it keeps out spam.
James

[asudavew]

That's a great layout.

Can't wait to see the finished project.