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CvC 03-20-2012 01:27 PM

Hearth insulation
Hi there,

I was looking for a cheaper alternative for ceramic fiber board for the insulation of the hearth and have heard of ovens that are insulated with gas concrete (the brand name in Europe is Ytong).
Has anybody here tried this and can report of his/her experiences?


Les 03-20-2012 02:09 PM

Re: Hearth insulation
If money is an issue why not use vermiculite? It's proven to work.

CvC 03-20-2012 02:22 PM

Re: Hearth insulation
Money is not really an issue, but on the other hand Im not willing to pay 300 (aprox. 350$) only for the insulation of the hearth, so Im looking for alternatives.
Vermicrete is an alternative, I just have to check if its insulating properties are as good as that of Ytong. (Is the name "Ytong" common in the states for gas concrete?)

Tscarborough 03-20-2012 03:12 PM

Re: Hearth insulation
It is better.

CvC 03-20-2012 03:49 PM

Re: Hearth insulation

Originally Posted by Tscarborough (Post 129051)
It is better.


do you have any facts?

Tscarborough 03-20-2012 04:53 PM

Re: Hearth insulation
I do, I have the same facts that you can find. Perlcrete can range up to 800 psi depending upon the mix, and a simple search of this site should reveal the posts where I researched it. AAC is brittle and fails under moderate to high heat, although that is not much of a factor for this use.

If you want advise, I gave it, if you want a report, I charge for that.

Tscarborough 03-20-2012 04:56 PM

Re: Hearth insulation
(I don't mean to be snotty, but the question is asked frequently).

Les 03-20-2012 05:46 PM

Re: Hearth insulation

Originally Posted by wotavidone (Post 129056)
I have read posts on this site that say vermicrete has a rating of 100 psi. ]

Even at this low rating it is more than adequate. The foot print of one brick can support over two tons. Multiply that by the amount of bricks in the circumference of the oven and you are talking an incredible amount of weight.

Tscarborough 03-20-2012 06:33 PM

Re: Hearth insulation
Yes, that is one of the most expensive things about building generic plans as FB has to do. For most people, the foundation, stand, and hearth slab are over engineered by magnitudes of degree. Of course some places need a seismic design and others need a 4 foot frost footing, but if the calculations are done individually for the specific location the specifications (and cost) can drop a lot, like more than 75%. The actual footprint PSI requirement for a normal oven foundation is roughly equivalent to ordinary compacted dirt.

CvC 03-21-2012 12:29 AM

Re: Hearth insulation

Originally Posted by Tscarborough (Post 129058)
Perlcrete can range up to 800 psi depending upon the mix

Thats a fact, maybe.
But this doesnt solve the problem.Vermicrete and Ytong are good enough at "normal" temperatures, no doubt about it. Complete houses are built using Ytong/Hebel, the problem is, is it still good enough to carry the oven dome after some fires?

By the way, in the FB plans, vermicrete is mixed with ordinary portlandcement, which is (also) not meant for high temperatures.

In fact, this mixture is proven to work, but what does this say abut the ability of Ytong?
Are the temperatures at this point (under the hearth and dome) not that high, or can portlandcement take more temperature than thought?

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