36' low dome neapolitan style

[Gulf]

The dome being placed or cut a little too far forward is no biggie. Some even do it on purpose. That's called a "beaver tail". It just takes some funnuy cuts to get back to circular and in most cases level. There are plenty of examples of that on the forum.

About the expensive mortar. Were you able to get a pic of the bag and or find out exactly what it was? Are you noticing any shrinkage in the wide joints? I was also hoping that it was not a "heat set" type of mortar. I do not have any experience with it. I do remember some discussions about it. But, that may not be the case anyway. If is setting up already it is an "air set" type of mortar.

On switching to hombrew. Anytime you see it is becoming necessary. But, save enough to true up the face of the vertical bricks of your entry arch since that is what was used for those courses.

[MarvinG]

Hi Gulf

Yes, now I have the specs for the mortar. does that tell you something to give me a hint regarding switching to homebrew straight away or can I continue a bit?

[Gulf]

I searched for the Isomat-AK-Fire mortar. It is an air set mortar. I did not see a maximum joint size recommendation, but they do mention 1 cm when referring to it's coverage rate. If you are not seeing any major shrinkage in some of the larger joints, use it up.

[MarvinG]

I searched for the Isomat-AK-Fire mortar. It is an air set mortar. I did not see a maximum joint size recommendation, but they do mention 1 cm when referring to it's coverage rate. If you are not seeing any major shrinkage in some of the larger joints, use it up.

Great, Thanks a lot Gulf

Today I checked the relatively big joints from the first and second round, and did not see any shrinkage. I mean its cold in my place and rather humid due to the temp, but its already rock hard what I did a 3-4 days ago.
One question: How does adding fireclay change the mortars abilities? For the last two courses I added about 1/4 of clay. Shall I continue with that?
For the 4th ring today I shaped the bricks to custom and was pretty angry when I (in the very end saw) that I have put some the wrong way so the joints are bigger than needed. I guess that's how we all learn.
HHere some pictures from today's X-mas work. :-)

All the best and Merry X-mas
Marvin

Ps: if anyone is thinking about buying a tile/brick saw (wet) or an angle grinder - go with the wet saw. On the market here I did not see anything reasonable for a reasonable price unfortunately.

[Gulf]

I'm not sure if adding brick dust to the store bought mortar is doing anything other than adding more aggregate. That may be what is helping reduce the shrinkage in the wider joints. (Adding that much unfired clay would probably make the shrinkage worse). It may also weaken the mortar. That may not be a bad thing as many store bought refractory mixes are not referred to as a mortar but rather a cement . Once set the joints can be harder than the firebrick. All ovens will crack. That is a given. Where they crack depends on what type mortar is used imo. I used a store bought refractory cement in my oven.The cracks run vertical across the middle of many bricks regardless of where the head joints are. A better suited mortar would have followed a zig zag course along the joint lines imo.

About what clay does for the hombrew. The theory is that once the portland burns out the clay and lime remain. Portland cement is only added to help speed up the build. I have a theory about regular clay and lime. When added together the mix wii react and set up pretty hard on it's own. My understanding is that is what many ancient builders used. I don't think that fired clayor brick dust will react the same way with the lime. But, the fired and unfired clay both seem to work whem mixed with Portland cement.

Just my opinion

[MarvinG]

Hi Gulf

Ok I see. I was also thinking that adding the sawdust might weaken the mortar, on the other hand it makes it a bit stickier imo, since the dust is extremely fine.
So you would say, if one shall pimp the mortar, only with sawdust, not with clay/schamotti.
If it's about homebrew, then one shall use fireclay instead of sawdust due to the reaction with lime.

Ah, this is new to me that all ovens crack. So why all the discussions? :-) I guess the ovens ability to store and throw the heat back to our pizzas is unchanged. Also due to the structure the dome is anyway strong enough. And since we have always 4 sides of mortar around the brick, if one or two crack, thats not really an issue, is it?
I'm only "concerned" once I have to lift the oven off and out of the window...thats gona be fun :P

[Gulf]

Going back to your post #44.

Today we found a local georgian Fireplace builder who said: This schamotti is "overburnt" clay

I'm focusing on the term "overburnt". There may not be much difference in how it performs than the brick dust . When clay is heated to a certain temperature it's properties will change. david s could tell us what that temp is . My personal theory about any possible reaction between natural clay from the ground with lime that has not been prefired is only that. My personal theory. I base that soley on the use of hydrated lime to stabilize clay. Where I live there is a lot of clay subsoil. Adding hydrated lime to the clay can turn it form from a wet bog that is impassible by vehicle trafic to an almost concrete hard surface. Again that is only my opinion. Brick dust and bagged clay have both worked well for me in the homebrew recipe. I have yet to try processing clay from the ground to see how it works.

There will be some cracks. The only masonry ovens that don't have them are those that haven't been used imo. As for as portability goes that will depend on the strength of your structural hearth.

[david s]

Both unfired clay and brick dust are not cementious materials and should be considered as aggregate in any mix. Although when fired clay reaches 573C it is chemically changed and is made permanent (won’t turn back into mud), becoming harder the higher the temperature goes from that point. This is above the service temperature of our ovens. Do not attempt to fire the oven really high in an effort to convert the clay or it will result in damage to the material. This change must be fired slowly and carefully to avoid damage (not possible with wood and a large air intake, you need a kiln to do this.
The advantage of brick dust is that as the clay has already been fired there is less shrinkage than unfired clay. It’s disadvantage is that it contains some larger chunks that require sifting out and as it’s better to add dry to get an accurate volume in the mix proportion really requires drying and re-pulverizing, which is more time and effort.

[MarvinG]

That is very interesting.
After a quick x-mas brake I have continued. Row 5 was already pretty challenging since the mortar I used is not very sticky, although I have added sawdust.
In the meanwhile I have also collected my materials for my homebrew. I nearly bought the quicklime, but notice early enough that it's not what we want.
What I have learnt is: the homebrew (3111) is a gamechanger when it comes to stickyness. It's crazy sticky, and row 6 holded super nice, did not even slip or so. But I made the mistake of not sieve my homebrew so I had a lot of little stones up to 10mm inside which is of course unacceptable.The homebrew also behaves quite a bit different. For the mortar it was pretty important to pre-water the bricks. Do you also do that for the homebrew?
I customized again most of the bricks so I would not have two gaps directly on each other. The rest of the homebrew i smeared around the oven - I guess that's what you guys use when you want to increase the thermal mass, correct?

Questions:
1: Since I still have a lot of sawdust, shall I use that for my hombrew or go with the shamotti?
2. How big can the gaps be for the homebrew?
3. Is the homebrew also the material to smear around the oven?
4. is there anything else to consider/foresee at this point?

david s : So, over time my oven will burn the the clay to stone, but I shall not force that, correct? Somehow my sawdust is super fine, that it would even be everywhere where I do not want it, so not really bigger chunks. It's more the sand which I bought (yellow sand) which has some bigger chunks which I need to sieve before using it.

Here are some update pics: I have also installed the burner so far.

[Gulf]

It's all looking good to me Marvin.

You definately want to sieve the sand to get out the pebbles. Some pebbles can burst when heated causing spalding. I use a window screen to do that. Actually, I screen all the dry materials before I mix the homebrew. I'm not familiar with your local sand but, it appears to have some clay content already. That is not a bad thing imo. I read where your prebagged mortar recommended wetting the brick. But, don't soak the brick for the homebrew. Just use a spritz bottle to place a fine mist on the surfaces if needed. If the brick are too damp a proper bond wont be achieved. The dryer brick pulling some moisture from the mortar is what makes the bond permanent.

(1) As I mentioned earlier, I don't know if there is that much difference between the brick dust and the "shamotti", since it is described as "overburnt" clay. Switch over any time you want.


(2) I don't like joints over 3/4". That is what is recommended. But, you can get up to 1" imo if you don't shave off the mortar as soon as you place the brick. Wait just a few minutes after placing the brick and then "tool" the joint. That is removing the extra mortar while also slight compressing it into the joint.

(3) The hombrew will be just fine if you want to add a little extra thermal mass. You can make it with the brick dust or the clay dust. The larger chunks from the brick cuttings are great to mix in here also.

(4) You are going to even out the face of your inner arch aren't you? That will be needed to be able to fit an insulated door to get a proper seal.

[MarvinG]

It's all looking good to me Marvin.


(4) You are going to even out the face of your inner arch aren't you? That will be needed to be able to fit an insulated door to get a proper seal.

Hi Gulf, thanks for these answers! Yes, I need a filternet as next for sure and hope I did not put too many lil stones in there.
Yes, my arch... that don't know what happened there. Looks pretty ugly now, but I'm going to grind and work on it a bit, and then place a slightly bigger arch with 1/2" overstand, so I can place a door. I will also try to cut some of my surplus blick in half to create flat pieces which I can use for the squirrel tail chimney. Buying flat firebrick in larger size is not possible here. Or in other words, some guys offered me st. but I don't trust it how it looked. (2nd hand). The channel for the hot air will then be divided into a left and a right side, but I need to plan it properly first. I will also need to add some with to my whole oven floor for the insulation. All not too crazy, but needs a bit of work - I'll keep you posted.

[Gulf]

From the pics, I can't see any need for grinding on the inner arch. I just see where the vertical sides need to be completed out to where they will be flush (even) with the segmental arch .You may also want to widen the vertical sides of the inner arch to get some more support underneath the springers on each side.

[MarvinG]

From the pics, I can't see any need for grinding on the inner arch. I just see where the vertical sides need to be completed out to where they will be flush (even) with the segmental arch .You may also want to widen the vertical sides of the inner arch to get some more support underneath the springers on each side.

Yes, the outer arch will be slightly bigger. I guess it shall be higher and wider, so the door seals fully on all surfaces?
Yeah, there is some grinding necessary, which you cannot really see, but the main thing is even it out to one level before I add the outer arch with the chimney section.
What did you mean by this? sorry, did not understand what you ment: get some more support underneath the springers on each side.

Here is an update with pics from today's session. Yeah, pretty dusty, soon I need my second diamond blade. But still, they hold impressively long (I bought one from Bosch).
The filtering of the homebrew was really worth it, super easy and quick too. Next row will be the 8th. How far can I go without support from your experience?
One brick, on the last pic comes out about 5mm, would you grind that back, since it's above the burner, so the aerodynamics of the flame are better, or am I going to far now ;-)
It's interesting the firemortar from the store is rock solid meanwhile - it's really more like a cement, where the homebrew hardens much slower and stays somehow brittle.
Tomorrow I will weld the stand a bit wider, so I have space for the chimney insulation. I was planning of mortaring the outer arch directly on the inner without any thermal bridge or how it is called. That's ok I guess?
And another question which went trough my head: How shall I start the curing fires with the burner? I mean it will directly burn the upper left of the oven which will heat up too quicky. Woudl you put some insulation there to protect it a bit from too much heat at the beginning?

Thanks, Marvin

[MarvinG]

Happy New Year everybody!

Here a short update from my side:
With the sticky homebrew it was fairly easy to close the oven. So far everything works as planned.
The last stone is put, about 1/3" of additional mass is applied.

The next steps will be:
- Add the front arch
- Squirrel tail chimney
- Add the pipe
- Add the insulation
- Start the curing fires

[SableSprings]

Well done Marvin! I like how cleanly you closed your dome. I also thought the lath strips to support the last few courses was a great solution. Looking forward to your next steps of 2021.