32" build in Calgary, AB - pompeii neapolitan

[IH123]

Because all concrete is somewhat porous you may want to consider adding a waterproofing additive to the concrete for the supporting slab, I use Xypex. Water wicking up from the base can find its way into the inner parts of the oven where it can become problematic and difficult to remove. This is highly weather dependent of course, but never allow sprinklers against the stand for this reason. Another solution to this problem is to paint a sealer over the top of the supporting slab, but I have no idea about its longevity or how a sealer would stand heat.
30 x 30 kg is a lot of hand mixing, have you compared readymix pricing? You should be able to pour the cores and slab top in one go.

1-moisture could go up or down and the more dams I put the more focused and damaging it would become, I think I will just leave it natural for now (no vapour barrier on top slab) and would have to protect the site from downpour, rain, snow, and ice melts- I will not manage gaseous level moisture. its my first build and as long as a risk is not of high impact I will ignore it for the sake of completing and hoping the solution can be made after a problem occurs (only for low impact risks)
2-I already have the 60 bags (4000psi) in my garage wrapped with vapour barrier above ground, I have bought used 4 cu ft drum concrete mixer. I did mix 28 25kg bags for my bottom slab (6000 psi with fibre) so 30 30kg 4000psi bags wont be different. I will pour the grouts first and then after a bit of cure the top slab (not both at same time, too risky for leaks and blow outs)

[IH123]

If not already in your plan, you may want to consider center supports on the sides. Strap and blocks are one option,

why? straps are better than stakes ? the only place I don't have stakes is the front however I have inserted 3" nail through bottom workform and into the edge so edge can't push out ( nail shear) , and to protect legs from slipping outwards I used small stakes for them. rear, and sides I can have as many stakes as needed. my worry about straps is the don't have enough tension at the middle of the lumber, and if I use very strong banding then the form could be twisted.

The picture shows cmu blocks dry stacked (or may be glued?), I had mine mortared with type s mortar and staggered pattern so only risk of leg/stud shifting is bowing under weight , I have more of them to compensate.

do you think its serious to have that support on the studs/legs? because if so I could just have a long lumber joining them together and then put another shorter set of stakes for them too