Hearth - vermiculite concrete or calcium silicate board? Newbie Forum Discuss Hearth - vermiculite concrete or calcium silicate board? in the Good Background Information forums; Hey oven lovers, I am about to start on my dome and am torn between what to use to insulate ...

[Ben & Relle]

Hey oven lovers,

I am about to start on my dome and am torn between what to use to insulate my hearth.

On one hand, the forno bravo plans call for a vermiculite/concrete mix which to me sounds like a lot of extra work as opposed to a simple calcium silicate board resting on the foundation slab.

Can anyone persuade me either way?

Cheers guys,

BEN

[ThisOldGarageNJ]

cal sil board is great stuff, I underatand many of the builders like it because it gives you a nice flat surface to lay your oven floor on, It also saves you mixing ther vermicrete floor which can be a little difficult... I mixed my vermicrete floor in a small cement mixer, which I've read is frowned upon, But it seemed to work fine for me and 6 months later still no problem.. If I were to do it again, I would go with the cal sil board just for the easier factor, Plus, someone correct me if im wrong,, you'll only need 2 inches of cal sil whereas 4 inches of vermicrete is recommended..

Mark

[dmun]

Vermiculite concrete: Less money, more work, more thickness
Cal-sil or mineral fiber board: More money, less thickness, potentially flat enough to lay floor bricks without leveling medium.

[RTflorida]

I did the vermicrete, at the time (2 1/2 yrs ago), the boards were pretty costly (about triple the cost of vermiculite concrete). Now that FB is importing them (as well as others), the cost has dropped considerably - although still a premium over the vermiculite, from what everyone says, it more than offsets the additional cost with time savings and ease of use. I would go for the board.

RT

[Ben & Relle]

Thanks guys.

I am thinking along the same lines. Cal sil board coast more, but it negates the need to fiddly form work to set it into, mixing, pouring, setting and such.

The cal sil board i am looking at using is rated to 1200 degrees celcius (who knows how much that is in fahrenheit).

For those of you who have used it - did you in any way attach it to the hearth? i.e. Did you rest it simply on dry fire clay (to level) or set it with a castable/fondue/wet clay or something similar?

I ask because I have been told that cal sil board should not get wet. Tech data I have read tells me it is OK to wet, but I'd prefer to ask those who have done it before.

BEN