First oven concerns

[Rich_ramaden]

Hi all, I've recently had a local builder create an outdoor kitchen area which includes a pizza oven. The oven base is reinforced concrete and the walls are double skin red brick (internal) and blocks (external) both then rendered (currently awaiting final skim). I started the curing process as per required and a small crack appeared down the centre of my base. This instantly caused huge panic and doubt on my side, with visions of a complete rebuild or the base collapsing. I've seen many ovens on sites with terracotta tile cooking areas and am wondering if I should add these to the cooking floor but worried it may make my entrance too small. So my questions are should I be worried? (I know cracks occur). Should I add a tile floor? How does it look generally? I'm concerned that if I get a really hot fire going the crack may get even worse. Thoughts?

[MarkJerling]

Welcome to the forum. Your oven design appears to be very different from the design most people on this forum follows. You have no under-floor insulation. It does not appear as if you have any insulation to your dome. I cannot work out from your post what your dome is made from? Your oven floor, as concrete, will not be able to handle the heat inside a pizza oven. While it probably will not collapse, the cracks will get worse and the cooking surface will most likely soon be a mess of cracked and broken concrete.

I would suggest that your brick and concrete base can probably be used to build a pizza oven on, but I cannot see a way to use the dome you have built. I could be wrong, but I believe you'll have to demolish down to slab level and start over.

[fox]

Like Mark points out …that ain’t going to work!
You might be ok re using the red brick depending on their makeup but, unprotected steel reinforced concrete will just crack and crumble.
The base will need some form of insulation and then a layer of fire brick or other refactory base on top.
The inner dome can be made from suitable brick but it then needs some heat resistant insulation followed by a waterproof shell.

[Rich_ramaden]

Hi both,
Thanks for the feedback, I'm not going to lie I'm a little disappointed. So, the done has an internal layer of solid red bricks and an outer of concrete blocks. It will have a render (what you see is the scratch coat). With regards to the base what would you suggest? If a complete rebuild can be avoided I'm keen to explore alternatives.

[Rich_ramaden]

[MarkJerling]

Hi both,
Thanks for the feedback, I'm not going to lie I'm a little disappointed. So, the done has an internal layer of solid red bricks and an outer of concrete blocks. It will have a render (what you see is the scratch coat). With regards to the base what would you suggest? If a complete rebuild can be avoided I'm keen to explore alternatives.

I think your best option, for the base, is to break down as far as the oven floor slab level (The one with the small crack). You can then lay an insulation layer on top of that and then build your new refractory floor on top of that. Feel free to look at my build photos which shows the process chronologically.

Start with the Forno Bravo "How To" guide. See here: Pizza oven plans - Build an Italian brick oven - Forno Bravo

I note too that your chimney mouth is at the very top of your oven. That will not work well as the chimney will 'rob' all the oven's heat. You will see that, if you follow the Forno Bravo plans, that the flue is actually outside the door of the oven, thereby creating a warm air volume above the cooking floor to cook the pizzas from above.

If you look at my photos, you'll see it looks like my oven's flue is at the top of the dome, but that's an illusion: I have a curved flue going from the doorway, up to the main flue outlet above the oven.

So, in closing. Re-use the base but start over from there. I cannot see any other practical way to salvage what your builder has built. Sorry!

[deejayoh]

That dome design isn't going work either, with the flue going out the top. All of your heat will go up the chimney. I'd ask the builder for your money back.

<<<Edit - see that I cross posted with Mark. What he said!>>>

[MarkJerling]

Oh, and another thing: The E-book is a free download as a PDF. So, it won't cost you anything but it really makes sense to have a read of that before you go any further.
How To Build Your Own Wood-Fired Pizza Oven (mailchi.mp)

[david s]

An updraft system with the flue exiting from the crown of the dome will work and in fact has some advantages.There are many ovens in private homes in Pompeii that utilise this system. Their two big advantages are firstly the elimination of an entry at the oven mouth which provides excellent acces to the oven chamber. The second advantage is that there are no smoke issues on start up as the draw operates really well even with the chamber being cold. This advantage makes this system more suitable for ovens inside houses. The big disadvantage is that the heat loss is far higher which contributes to a much increased fuel consumption. The larger the oven chamber the greater the fuel consumption becomes, so in the case of the large Pompeii bakery oven, the design most of our ovens are based on, the fuel consumption would have been a dominant factor. Also being fired every day meant that the chamber probably never got cold, so the smoke issues would have been largely eliminated.
The first oven I built was based on Ancient Roman kilns which had their flues at the crown of the dome. However beiig full of wares when being fired allowed the flame to pass through and around the wares before exiting. There are many updraft ovens being built, sold and fired. They do work, just not as efficiently as the cross draft system.

[NCMan]

I agree w/the others and don't see much there worth salvaging, other than perhaps the base, possibly the slab. It may even be good to rip out the slab, too. After all, everything from here on out will set on that slab. It's important. I certainly wouldn't want to build on it w/that crack through it, especially not knowing much about how it was poured. Just my opinion. Best of luck to you.

[MarkJerling]

I suppose if it has adequate steel, then the little crack won't matter, but if it's short of steel, then I'd agree that it would make sense to redo the slab as well.

[NCMan]

One thing that's seen quite often is builders shoring up the center section of the slab, w/out using shims under the bracing, then later taking a hammer and knocking out the board(s), which can and does crack the slab, whether it's reinforced or not. It's important to use shims in places like that, so the bracing can be removed w/out causing damage. There's no way of knowing if that happened here, but there's a good chance it was.