Insulation questions

[Dutchoven]

Ed
Hopefully this can help you...here on the forum we refer to a structural slab that is beneath the vermicrete/ceramic fiber board or combination thereof...then goes the firebrick floor...I personally don't think that you will overheat the floor just simply thanks to the firebrick finding equilibrium...depending on the design of your block walls and how you are reinforcing the structural slab could be thick or thin...someone correct me if I am wrong but I think the plans spoke of 4 inches thick on the structural layer?...as far as the cladding goes...I am on the fence as to the necessity of thick cladding of concrete...especially if when you design you vault arch you don't use a full height brick for the soldier course and are careful to fully encase the catenary arc in the brick...
Best
Dutch

[glennb]

Originally Posted by ironchefshort

So if I were to go the route of having 2 courses of firebrick for the hearth, equaling 6.75", I would then place the CA board directly underneath the firebrick hearth. Under that would go the vermicrete layer followed by the hearth slab. Am I correct in my thinking? How thick would I need to go for the hearth slab since heat retention is no longer the main purpose?

Ed

Ed,
That sounds about right in order of materials. You could simplify your build by using all vermicrete or all CA board under the firebricks though. I would use the CA board, maybe as a double thickness (2x2" boards) on the concrete slab as insulation between concrete slab and firebricks. This will also give you a nice level surface to place the bricks on too.

Concrete slab should be ~4" thick with reinforced steel (mesh or bar) throughout the slab to provide structural support only (no heat should go into this slab).

[gjbingham]

3.5 - 4 inches for the hearth concrete sounds right. The purpose for using refmix, from my understanding, is that it has properties that are very close to, if not identical, to that of firebrick. This is a good thing because the mortar will expand and contract the same amount as the bricks during thermocycling. Fewer broken mortar joints (cracks) is the intention.

Additionally, the refmix adhears much better to the bricks (I hear) than the homemade variety.

That all said, I used the homemade variety.