my neapolitan style oven in progress

[Hampelschwein]

ah right, thanks. Than I will probably make something removable, something like this https://youtu.be/sM9zteuE8UA?t=274

[Hampelschwein]

I'm not sure about the gaps between the pizza stones and the ones between the pizza stones and soldier. I now filled those gaps with clay, but I don't know if they need space to expand in the heat or would crack otherwise? Any thoughts on that?

[UtahBeehiver]

At least in the pompeii ovens , we suggest an expansion gap around the perimeter about the thickness of corrugated cardboard and just let the ash from the fires fill the gap in. The floor and the soldiers will expand and contract at different rates. This could cause cracking or heaving if there is not enough of expansion gaps. But you have already, filled them in so it is what it is.

[Hampelschwein]

as its just natural clay which would only completely harden when I make the fires inside I could probably still scratch it out of the outer circular gap...

[briram]

Hampelschwein what kind of bricks are you using and from where do you get those? I am glad to see someone from Germany doing great stuff so that we can share information about suppliers.

[Hampelschwein]

briram , I was lucky with the bricks. When I went to visit my blacksmith in his workshop place close to Dresden I asked him if he knows an affordable supplier. It turned out his neighbour was an oven builder who had a lot of bricks left over. Most of them used. But this was how I could get them for cheap. The stones I used for the hearth I bought at Kamingroßhandel Dresden who have the stones from the factory in Radeburg.

[Hampelschwein]

So finally I finished the cuppola after tetrising the entrance area!
I've build a gravel form with wood underneath so that I didnt have to get so much gravel. (Yes the wouod pieces are small enough to get them out of the entrance later ;-) )
At first I set the bricks by putting mortar both to the side facing down and to the left and right side, but then continued only with mortar on the downside as I've seen it Stefano Ferrara do. When I finished setting the bricks I made a much more liquid mortar mixture to fill the gaps, also like I've seen it Stefano do. Still I tried to keep it as firm as possible as long as I could be sure, that the mortar would completely sink into every little gap. The morning after, what I feared happening happened, there were some cracks in the mortar. Is it something to worry about? Hard to imagine you can avoid them with liquid mortar. They don't look too drastic I think/hope.
As the next layer I'm planning to put some insulation fiber stuff on top (quite a bit over the dome and about a centimeter on the sides of the soldier).

[Hampelschwein]

[Hampelschwein]

somebody knows what kind of insulation/fiber mat stuff is best to use for the next layer?

somebody knows what kind of mosaic and mosaic mortar/glue is best to use?

[UtahBeehiver]

A high temp ceramic fiber blanket (not rockwool or fiber glass insulation) is your best bet for the oven since you get the most insulation value per inch. The sides of the oven limit how much you can install due to the metal ring on the stand. The top you have more flexibility to install more. I do not know what your winters are like but I did polished glass in concrete for the counters and my oven is exposed to the elements. The concrete/glass counters have "not" held up well to our harsh Utah winters, a lot of spalling and glass working loose.

[Hampelschwein]

thanks,
in Germany the winters are not too harsh anymore. Last year it almost didnt snow at all and every year it seems to get milder, but it rains quite a bit and also falls below zero form time to time.
Which sucks in general, but might at least be good for the oven.

I've been preparing a casting mould for the opening of the chimney above / in front the entrance. The inner metal ring is steel, the outer some thinner sheet metal. The floor is wood which I will remove later.
The plan is to put some reinforcing bars on top of those distance keeping screws and to fill it at first with some refractory mortar, and put a row of narrow upright firebricks on top continuing probably with normal mortar/cement whatever on the outside.
The outer sheet metal I want to remove after it is dried, because it looks ugly and will be difficult to attach plaster to. After fixing this thing on the oven I will put a pillar under it before putting the mortar and bricks. I'm a bit worried about the stability of the joint at the oven, but I hope it will get stability as soon as I combine it with the rest of the oven so that it gets held from above in a way.

[UtahBeehiver]

I think you should get feedback from DavidS on rebar in casting. I know he has had some real life issues with corrosion or expansion with rebar in casting but it may no be as big a issue since this is on the front opening.

[david s]

Rebar is not recommended in conjunction with castable refractory, The recommended reinforcing is melt extract fibres (stainless steel needles) Heavy rebar will expand more than the refractory that surrounds it in higher temperatures whereas the needleshave a larger surface area and can conduct their heat more readily creating less of a problem on expansion. In addition the stainless isn’t prone to corrosion like the mild steel reo. A practical example of this problem came up a couple of weeks ago, see here
https://community.fornobravo.com/for...ons#post414646

[Hampelschwein]

holy shit, thanks for saving me from this!
It's a bit difficult to research those needles. Could you give me a vague idea how big one of those needles should be? Right now I can't find places in the internet where this stuff is sold. Maybe I didnt find the correct german term for it... Stahlfasern, Schmelzextraktfaser, Metallnadeln didnt really lead me to a seemingly suitable product.


David, as there are problems with the compression of ceramic fibers mentioned in the post in your link, do you think it's critical to use them on top the cupola and above that a maybe 15cm thick layer of perlete mixture or some mixture with expanded clay? Or how thick would you recommend this ceramic fiber layer to be? They seem to be available in 13mm and 25mm, but I rather thought doing 5cm or even thicker. I wouldnt want the mixture above to crack because of the compression...

[david s]

The correct name for the stainless needles is melt extract fibres. They can be obtained from refractory suppliers. Size of mine is 25 x 0.5 mm. They are expensive, make handling more difficult (not called needles for nothing) and are absolutely necessary. Most cast oven manufacturers don’t use them (I don’t think Forno Bravo do).
Regarding the compression of ceramic fibre blanket, it is really only a problem under heavy floor bricks. On top of the dome of a layer of vermicrete is applied over the blanket and allowed to set hard, it is quite strong enough to hold plenty of weight for any heavier layers over it.