Circoular Concrete Base for my oven

[Lucag]

Hello,
Luca from London here.
I am building a Pompei oven on a round structure of 140cm diameter ( see photo).

Could you comment on my plan?
---------

- As soon as I reach 80cm with the brick wall I will add a concrete Base for my oven (I am thinking 5cm thickness)

- on top of that I will add ( 10cm of vermiculite + perlite + cement with 5:1 ratio )

- I will then pose 42GD firebricks on 2mm sand as a Base for the dome.

I also have some direct question:
---------

- do I also need a 25mm calcium silicate base to be added between the 5:1 perlite cement and the firebricks?

- I did the concrete round foundations easily but I am unsure on how to do the round concrete Base for the oven: do I use a wood framework and then life the concrete and remove the wood?

- can I skip the 5cm thick concrete Base and do a 15cm thick Base made of perlite and cement 5:1? Will it be strong enough?

[UtahBeehiver]

Welcome from the UK. Nice looking circular base.

IMHO opinion here are my answers (not knowing the size of the oven.

10cm of pcrete 5 to 1 is minimum thickness.

5cm (1.96") hearth base is not thick enough, you should have at least 4" (abt 10 cm) reinforced with rebar - these ovens get quite heavy.
What are dimensions of 42GD fire bricks.

CaSi not needed with the 10cm of pcrete but you could make pcrete thicker instead.

I would form hearth in place, this will be heavy. Use bender board to form and properly supported on sides to prevent blowout during pour.

Cannot sub pcrete for thicker concrete hearth, Pcrete does not have the structural strength.

[Lucag]

Thank you for your reply

Diameter of the heart Base is 140cm, I haven't decided on the oven internal diameter, but probably 90cm.

For the dome I can easily buy online 230x114x64mm 42gd can I use the same for the floor? Happy to reconsider any other brick size, even for the dome: I haven't ordered anything yet.

Following your suggestion I will go for 10cm armed concrete and 20cm pcrete (5:1) on top

One question remains. If you pour the concrete hearth in place, how do I remove the wooden board when the concrete is all dried up? can I just leave the wooden board there?

[UtahBeehiver]

If you use a concrete fiber board backer(commonly used for tile) and make it slightly larger than the ID of base you can leave in place. You must have to adequate support the board from underneath during the pour. I will let other chime in on whether to leave wood underneath since I did not do this. One thing for for sure is to put a couple drain holes in the hearth slab for drainage of water.

[agrasyuk]

You can make your ply board from components that can fit through the opening once broken down. Like saw the circle in half and hold it together with screws . I imagine supporting such structure across the entire perimeter will be quite of a challenge though. IMHO you are much better off with larger leave-in-place cement board like Russel suggested

[Lucag]

This worked out pretty well! I am now ready for the next phase, floor insulation and the dome. I am thinking 5cm cal sil board all over the base, 0.5mm of normal sand and then fire bricks for the oven floor.

would that work fine ?

[UtahBeehiver]

Sand is not necessary if everything is level, a sand/fire clay mix is used for leveling purposes only.