Insulating Firebricks

[cleverdick]

I'm wondering about using 76mm insulating firebricks between the slab and cooking floor. It seems to me that it might be good because: (1) That's 3" of insulation, and (2) it avoids any risk from hazardous fibres that might exist in proprietary insulating board. My only concern is whether insulating firebrick will be strong enough to support the dome and cooking floor without crumbling, particularly when subjected to the expanding/contracting of the dome assembly.
Also, what about using insulating firebricks for the arch? I figure that would be good for keeping the front wall of the enclosure cool, but otherwise I'm not sure....

[GianniFocaccia]

Re: Insulating Firebricks

Insulating firebricks are plenty strong enough to support the floor, but at $3-$4 apiece it'll cost you $250 (give or take). Vermicrete has the same insulating value, can be poured thicker than 3", can support a floor and dome, and is a quarter of the cost of bricks.

Insulating bricks are very light (full of air holes) and easily abrade. They are not suitable for any part of your dome.

[Lburou]

Re: Insulating Firebricks

Insulating firebricks are plenty strong enough to support the floor, but at $3-$4 apiece it'll cost you $250 (give or take). Vermicrete has the same insulating value, can be poured thicker than 3", can support a floor and dome, and is a quarter of the cost of bricks.

Insulating bricks are very light (full of air holes) and easily abrade. They are not suitable for any part of your dome.

I discovered one more thing about insulating firebricks....They float in water!

[dmun]

Re: Insulating Firebricks

Insulating fire bricks are about equal in insulating value to vermiculite concrete, meaning that you will need at least four inches below your floor. As GianniFocaccia points out, They work fine but they are not for the cost sensitive build. Like all insulation materials, they have plenty of compressive strength.

You don't need to worry about the safety of cutting insulation materials if you are using a respirator, as you should for all masonry cutting, including insulating fire bricks.

No insulation material should be exposed to the interior of your oven.

[cleverdick]

Re: Insulating Firebricks

Mmmm...

It's looking more and more like vermicrete is the way to go...

I suppose my initial reservation was because I always thought that heat + aerated concrete would result in an explosion!

Presumably the vermiculite gives a cushioning effect and stops it shattering!

Is that a fair assumption?

[eprante]

Re: Insulating Firebricks

Dick,
It works and its cheap, and no one will ever see it. This stage becomes almost a sickness because you can't stop thinking about the oven. No need to reinvent the wheel here. Get beyond this stage into the fun part- building the dome
Enjoy,
Eric

[dmun]

Re: Insulating Firebricks

Insulation Fire Bricks if Vermicrete is as good, they would certainly use it in furnaces but they don't.

They certainly would use it in furnaces if they fired them to 1000f. Different temperatures, different insulation.

insulating fire bricks is that they do not expand with heat

Everything expands with heat except ice.

anything with Portland cement has a tendersy to move with heat causing cracking in what is built on top of it.

Vermiculite concrete is perfectly stable at the temperatures we use it. Is it the best insulation? It's the best value if you're on a budget.

in other words don't mortar your first course to the vermicrete.

Exactly right, nor your floor either. An oven is an object in motion.

[Johnny the oven man]

Re: Insulating Firebricks

Vermiculite is rated well over 1000f, in fact it is exfoliated at 1200c, so 1000f is a walk in the park, you just have to get the binder right, that is where cement fodue comes in to the equation at the higher temperature requirements.
The reason vermicrete is mainly used is lightness AND insulting qualities.

[Johnny the oven man]

Re: Insulating Firebricks

The one thing about insulating fire bricks is that they do not expand with heat anything with Portland cement has a tendersy to move with heat causing cracking in what is built on top of it. You need to have a floating floor and build your dome on that in other words don't mortar your first course to the vermicrete. I also beg to differ on the insulation qualities of the Insulation Fire Bricks if Vermicrete is as good, they would certainly use it in furnaces but they don't.

Doug

Vermiculite IS used extensivly in furnaces as an insulation product. It is used in both sheet form and loose fill.

[GianniFocaccia]

Re: Insulating Firebricks

A UK firm (Vitcas) manufactures vermiculite board as insulation and strangely enough, firebrick replacements in wood stoves. Rated to 1000*C, I think this board is a little overkill for our application but the fact that we can manufacture such a cost-effective
insulative layer from common materials purchased from our local box store is way cool.

[david s]

Re: Insulating Firebricks

"Vermiculite is rated well over 1000f, in fact it is exfoliated at 1200c,"
The exfoliation is done at around 540 C- 810 C, but still well over the 1000 F

[brickie in oz]

Re: Insulating Firebricks

Ppl seem to get so anal about all the what ifs?
Just go and build the thing and enjoy the benefits of a WFO.

[dmun]

Re: Insulating Firebricks

Some like myself used Insulation Bricks some used Insulation Board others used Vermiculite Mix it does not matter as they all work.

Amen. If we start spreading the word that the only good solution is the difficult, expensive solution, we may discourage potential builders.

[Neil2]

Re: Insulating Firebricks

The vermiculite mix has been used by literally hundreds of builders on this site with success.

It is cheap and easy. I'm convinced it is the best solution for the DIY builder for the under hearth insulation. The FB board insulation also works well and for some may be the solution since it doesn't involve the formwork, pouring and leveling that the vemicrete requires.

[Johnny the oven man]

Re: Insulating Firebricks

We know that vermiculite is well rated but what about the cement that is used in the mix.

Use cement fondue, a high temp. calcium aluminate product from a company called Kerneos.