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]

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]

Originally Posted by GianniFocaccia

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]

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]

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]

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

[Karangi Dude]

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

[dmun]

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.

[Karangi Dude]

Everyone to their opinion

[Johnny the oven man]

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.