Engineering the Hearth Base

[RGJ]

I've read the FB building plans, and I've looked at lots of builds.

Looking at the FB plans, it looks like I'm to pour a 3.5" reinforced slab directly on top of the cinder blocks. They don't suggest doing anything fancy with the re-bar reinforcements. The slab is completely supported by the cinder block. Correct?

I've seen other builds online where the builders notch the cinder block and lay the re-bar reinforcements in the notches & then pour the slab around the re-bar. Is this a better design? Instinctively, it seems so, but when I think about it, in either design the entire weight of the oven is supported by the cinder block.

Engineering for this kind of weight seems an important point, so any clarification is appreciated.

Any strong feelings about using Hardibacker as a permanent base for the concrete instead of removable plywood?

Also, on hearth insulation: I've purchased the FB insulation board to use as the hearth floor. Is there any benefit to adding a layer of insulated concrete between the concrete base and the insulation board or am I just adding unnecessary mass? Alternatively, is there benefit to floating the insulation board in a layer of insulated concrete? The oven will be used quite a bit for baking bread but certainly not on a commercial scale.

Thanks for your help!

[UtahBeehiver]

There are host of well documented builds in the Newbie Section under sticky called Treasure Archives or something to that effect.

3.5" hearth with #4 rebar 1 foot on center is plenty good.
I filled every other core on the cmu with rebar placed in base slab then tied to hearth rebar grid.
Use durarock or equiv under hearth and just leave in place. Make sure you support from underneath well during pour.
Most users are fine in 2.5" thick fire brick floor for extended usage and bread. Commercial and serious bakers will add additional thermal mass in the floor, more the exception than the rule.

The most import item for a good performing oven is "GOOD floor and dome insulation"