new build Q need an A

[Cypress]

I have been reading for a while here and planning even longer. I have poured my slab and getting ready to start my stand. My slab is 6?x6? with 24? beams and ? rebar. I am now getting started on my stand. My first real questions is would it hurt to put concrete in all the hollow cores of the cinder blocks or should I just fill every other one as directed in the plans. I plan on cutting out the dividers on the top row of blocks and make a beam for the hearth slab. The other concern is that I wanted to pour a 7? hearth slab 3.5 vermiculite and Portland. Is there any benefit to pour a retaining wall for the vermiculite? Is the thicker slab going to create more thermal draw? Any advice would be greatly appreciated. And I will post pic soon.
Best Regards,

[exceloven]

Re: new build Q need an A

Welcome and congrats on your start. I filled all the cells of my block, just makes it that much stronger. As far as the top course, they make bond beam blocks which are blocks with the center recessed a couple inches for steel. If you buy those for the top course it will save some cutting. As far as the retaining wall for the vermiculite, I'm not quite sure what you mean. I poured my hearth slab with a form in the center so the finished hearth would be my form for the insulated slab. There are pictures of it on page 3 of my thread (Marks WFO). I'm sure there will be a lot more help following!

Mark

[Neil2]

Re: new build Q need an A

"I wanted to pour a 7” hearth slab 3.5 vermiculite and Portland."

You need two layers. First the structural layer. A 4 in thick reinforced concrete layer should be all you need. This can be supported by the walls of your stand - you do not need additional interior beams.

On top of this is the insulating layer. I suggest 4 inches or so of vermiculite 8:1 mixture. No stronger or you loose to much insulating value. An 8:1 mix is plenty strong enough to support your hearth and dome. No reinforcing steel.

On top of this go your hearth bricks. These, along with the dome bricks are part of the thermal mass. This thermal mass should be, as far as possible, completely surrounded top and bottom by an insulating layer.