32" build in Calgary, AB - pompeii neapolitan

[IH123]

Finally the build started, I cut bricks to desired shape (which was actually a lot of work to cut enough for just one course, it went will, just one thing , I should have dry fit before I mortar, resulted in one course loosing staggering with the one below so had to leave gap to keep staggering, tomorrow will cut one and fill it while cutting for the inner arch intersection. it could easily take a full day to cut and build just one course:

1-pictures of trammel mounted (actually mounted loose, I can re-put after each brick)
2- picture of build of part of course#1
3- picture of dome cut brick (7 cuts total: cut in half->Left wedge->right wedge-> top taper -> top taper remaining thickness (10" saw not deep enough)->bottom tapper-> bottom tapper remaining thickness)
4- one of the bricks got stuck by the hearth and because how the trammel is pushing on the hearth, by time I was trying to fix it the mortar was hard so it did not adjust very well, but will ignore as its less than 1/4"-1/2" off course (outwards)

[IH123]

I had to modify it further, removed the L angle steel as they are very high and placed the trammel vertical axis directly in the lazy Suzan bearing by twisting the holes up. now its 5/8" exact high, which is exactly what I need to place it directly on insulation without the need for any levelling, I have to support it by creating a hollow square in a wood board where when lazy Suzan lower plate get stuck in the square it can't move , while top one does, the board has to be thin near the bearing plate:

[UtahBeehiver]

That is much better. Should work good with no stepping error.

[IH123]

I have refined my trammel now its much better, it will need more sturdy nuts and bolts which I will put when I have a visit to the hardware store:

1- now vertical axis is almost same plane as brick centre when its in clamp jaw
2- the line from the vertical axis to the brick face is perpendicular

[IH123]

I placed today the cornerstone of the inner arch, I noticed that , the stone is connecting the dome to the archway base on top surface (archway hearth), wondering if I should use my angle grinder to remove that mortar joint line between the archway brick and the dome course#0 brick shown below, or likely it wont bridge much heat as its only 4.5"x4.5" - there will be 1/2" fibre glass rope gasket between (in front of ) the inner throat archway legs and voussoirs and the archway arch legs and voussoirs , just this first base brick is not, thinking this arrangement would keep the hearth clean of multiple gaskets and for food sanity...

?

[IH123]

It looks like for dome course#0, I used exact cut however also used 1/8"-1/4" mortar thick as the cuts ended up smaller than the desired(I allowed it for mortar) resulting in using only 27 half bricks instead of 29 half bricks . so I now calculated the new brick cuts when using 1/8" mortar and I will tune my jigs to get exact final cut:

[david s]

Be careful

"firing of an uninsulated oven is asking for trouble because of the huge temperature difference between the outer and inner surfaces of the inner oven"

There are many reports of ovens cracking because builders have fired them with no insulation in place.

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/471066-32-build-in-calgary-ab-pompeii-neapolitan?p=472605#post472605

[IH123]

I , today, wrapped a 1/4" ceramic fibre paper around the dome bricks course#0 and then applied two straps of stainless steel banding (0.03" thick 3/4" wide), I tension-ed a little just to keep ceramic fibre paper in place with some compression, I did not even close the clip, will re-tension after oven firing when oven is hot, before applying ceramic fibre mat and dome render.

I , as well today, mortared the bricks for the archway , first course (hearth level) only, making sure that they are levelled

I did seal the gap between the dome brick and archway first course with about 1/8-1/4" refractory mortar to seal ceramic fibre paper in archway (from the dome banding paper) , however I later scrapped it not wanting to bond the archway to the dome, I will later on next work on it put a much thinner layer to seal the ceramic fibre that is too thin to become a bond

next, I plan to position the arch forms and start cutting and dry fitting all the three arches, before building any further dome bricks, I am considering completely building the inner throat arch (only) as well as the flue gallery and mouth (outer ) arch legs (only) as well before building the dome bricks.

pictures from today's work:

[IH123]

Today, I finished mortaring the first course of my dome (spring line course#0, which is 2.625">>2.19" on top face, bottom un cut and 4.5">>3.52" on left and right), I used parchment paper under the dome bricks so no joint mortar will touch the insulation mortar coat, I only put mortar on joints, I did not put any mortar bed or slurry at all, just parchment paper. I however to seal the cooking chamber from dome outside and render after parchment burns, I put a thin mortar layer outside of the dome brick where brick meets insulation coat so that its sealed, unless it cracks from gas pressure, its fully sealing any gaps between parchment paper and brick/insulation coat (of course I removed any excess parchment paper with a sharp tool before sealing with mortar. I then put the pre-cut hearth bricks in place. I filled the gap between the hearth and dome bricks, which was a bit larger than intended of 1/4" with brick cut shims to keep the large gaps closer to 1/8", I plan after firing the oven and having ash, to vacuum everything in the gaps and fill it with pure fine ash.

I am now ready to build next course, course#1 (2.625”>>2.05” top/bottom, and 4.5”>>3.52” left/right), but after I set up my trammel or template tools above hearth as my sphere cap centre is 2" below hearth brick top surface, and after I place the actual stainless steel banding snug (to be tightened after firing while oven is hot and expanded, and after I mortar my throat and mouth arch legs to mark the space for dome build

here are the picture from today's progress:

[IH123]

As mentioned before, the left red line point needs to intersect the vertical center of the brick face or you get a cumulative error as you move up in the courses resulting in a stepping of the brick course. It is cumulative and gets worse as you go up.

the measurement I made applies to any line on the clamp as its perpendicular to the clamp jaw, and when I place the brick, I will place it such that the centre of the brick is at the centre of the clamp jaw - thank you. I can slide in a board of same width as brick with edges locking it to clamp jaw that it grantees brick in centre if placed within its width.

I had a field trial today and I realized the following:
1) with my clamp bar screw on the outside, after placing a brick(I did it dry of course), when trying to move the tool upwards it will knock the brick away upwards with it because of the angle lip. the only way regardless of where the length measurement line hits the brick, to get the tool not to knock the brick away is to have a screw on the inner side as well.

so, as I am missing the screw on the inside, I will try tomorrow to use a 1/8" wood board shim that I place between the inner bar clamp jaw and the inner brick face and might have to put on it slippery substance like a parchment paper , so after I finish placing the brick and unscrew the outer screw, I will pull the 1/8" board shim may be sideways, while it may still shake it a bit it might be less especially if i pull it in the direction where I want the brick to compress for its head joint. that one is what I could use to help aid centre the brick on the clamp jaws.

2) i am not going the route of using welding to make my custom tool because once I build the first-2nd course and reach above the hearth, I could use the quarter circle template that I made to align the brick if it shakes after removing the trammel clamp upwards.


I am going next, to adjust the trammel length to be correct with the introduced board in jaw, and then remove all hearth bricks or most of them in centre to install trammel above insulation, build my 1-2 first courses of the dome using the trammel and then put the hearth and protect it by cover and then start building using the template not trammel. might be something different like delaying laying hearth until couple more courses just not decided how yet:

1/2 brick high is 2.625"/2 = 1 5/16", therefore I should draw a line from top of clap jaw down 1 5/16" and then 16" to the axis, and use 1/8" board shim to slide sideways

but honestly, I forgot that I have a release button at the inner jaw clamp so that solves the issue of not having a screw, still the issue of the angle between axis line to jaw and the jaw plate are not perpendicular need a board shim to correct it

[UtahBeehiver]

As mentioned before, the left red line point needs to intersect the vertical center of the brick face or you get a cumulative error as you move up in the courses resulting in a stepping of the brick course. It is cumulative and gets worse as you go up.

[david s]

On the theme of thermal expansion, generally for the service temperatures we take our ovens to, the expansion is not much of a problem because it's only around 0.5-0.7% (or 5-7 mm for every metre). However, as this thermal cycling occurs every time the oven is fired it is constantly expanding and contracting. The analogy of an expanding chest during breathing is a good one. A tight belt around the chest simply restricts free and easy breathing.

Water elimination, expanding steam and steam spalling is a completely different issue.

A semi-circle arch is a relatively stable form two dimensionally and improved in three dimensions, but not completely self supporting. The only true self supporting arch is the catenary arch and it is unfortunately an unsuitable form for an oven because of the low angle at the base and the high crown. In its three dimensional form the catenary dome requires no assistance from either buttressing or bracing. See "Pizza oven becomes a kiln"

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/other-oven-types/14564-pizza-oven-becomes-a-kiln#post14564

Because kilns experience more than double the service temperatures to that of an oven and the corresponding more than double thermal expansion experienced, methods of supporting the structure were developed. Ovens are not kilns, but the same principles apply. Heavy buttressing introduces energy sapping thermal mass, so lighter weight steel bracing is usually the preferred method. The greater the arch radius, the greater the outward thrust and the greater the need for support.

If an oven cracks, and many do, it is simply creating its own expansion joint where it needs to. The usual method for refractory engineers designing kilns and furnaces, is to observe where the cracking occurs and then engineer expansion joints at those positions.

I believe it is preferable to allow the inner oven to expand and contract freely within the outer shell, allowing the insulation layers to act as the expansion joint. But the firing of an uninsulated oven is asking for trouble because of the huge temperature difference between the outer and inner surfaces of the inner oven.

[IH123]

I had lowered my indispensable trammel tool axis even more, after I finish assembling the hearth, I will try to confirm it can fit above insulation with little shims, and if it works then I will create a wooden brick to hold it otherwise will have to lower the axis even further.now the top of the brick will be very very close or even lower than where all axis meet so may even have it closer to hearth than before, going to test it on real radius on oven to figure out:

[IH123]

Over the last few thousand years, the most popular all round oven form has been the hemisphere. It has of course advantages and disadvantages. As a combustion chamber it has no competition as the auto industry also knows, Its advantage in building, as eons of Ancient Roman architecture shows, is ease of construction, utilising a semicircle and employing the self supporting qualities of the form which do not require (or minimal requirement) for buttressing or bracing. Although thermal expansion and contraction really test this quality. As a baking oven its circular floor makes loading difficult and tall baking pans cannot utilise the perimeter because of the dome vault being in the way. The Neapolitan oven, developed in Naples to increase output by higher temperature employing a low dome, which creates greater radiant heat because it's closer to the food, works well to cook food fast. Unfortunately the price it pays is reduced structural integrity because of the much greater outward thrust created by the expanding larger radius vault. The method used was to get height at the perimeter by using a soldier course and steel band to counteract the outward force, rather like a tight belt around the chest which restricts easy breathing.

The attached drawings should explain all this better.

In the case of your oven as your course 0 is not actually in the chamber, those bricks will not be as hot as those above them and as they will be restricted by the steel band, will result in plenty of stress between course 0 and course 1 which is not restricted, but expanding more. You will have to wait and see how it works, but I fear there may be a problem at the mortar joints between these two courses.

There will be no stress between course#0 and #1, the reason is the stainless steel banding will be only tightened while the oven is hot, so after first firing when the oven fully cured and reached its final highest temp and before putting the dome render insulation, the band will be tighten, carefully , and lightly, while the oven is still hot, which means fully expanded. therefore no stress on any other than the expected between any two brick joints. regardless if its full sphere or not, there is always a thrust at joint , either fully downwards(course#0 bottom) or fully horizontal (at pole) and 1/2 in each direction at 45 degrees joints, the stress is always there however the shape of the brick and its rigidity as well as mortar flexibility will prevent any cracks:


1)my course#0 will NOT be mortared at bottom,only joints, so it can slide
2) banding will be tightened only once while oven is at its hottest
3) I will apply on the outer most edge of course#0 brick faces where it meets the insulation coating a thin layer of refractory mortar to seal the render ceramic fibre mat dust from entering into cooking chamber. because brick will expand on the inside face as its hottest, it will move inward toward dome centre than outwards, therefore a thin layer to close any gaps on the out will either never crack or if it does will be easy as its too thin to prevent the movement of dome

[david s]

Over the last few thousand years, the most popular all round oven form has been the hemisphere. It has of course advantages and disadvantages. As a combustion chamber it has no competition as the auto industry also knows, Its advantage in building, as eons of Ancient Roman architecture shows, is ease of construction, utilising a semicircle and employing the self supporting qualities of the form which do not require (or minimal requirement) for buttressing or bracing. Although thermal expansion and contraction really test this quality. As a baking oven its circular floor makes loading difficult and tall baking pans cannot utilise the perimeter because of the dome vault being in the way. The Neapolitan oven, developed in Naples to increase output by higher temperature employing a low dome, which creates greater radiant heat because it's closer to the food, works well to cook food fast. Unfortunately the price it pays is reduced structural integrity because of the much greater outward thrust created by the expanding larger radius vault. The method used was to get height at the perimeter by using a soldier course and steel band to counteract the outward force, rather like a tight belt around the chest which restricts easy breathing.

The attached drawings should explain all this better.

In the case of your oven as your course 0 is not actually in the chamber, those bricks will not be as hot as those above them and as they will be restricted by the steel band, will result in plenty of stress between course 0 and course 1 which is not restricted, but expanding more. You will have to wait and see how it works, but I fear there may be a problem at the mortar joints between these two courses.