42" Pompeii construction in Adelaide

[P3 Stoaker]

Meant to ask. What does everyone think about how tight to lay floor bricks? I’m using a 12” square 2 “ thick fire brick/ paver layed on Cadillac board with dome on top of floor??

[NCMan]

Meant to ask. What does everyone think about how tight to lay floor bricks? I’m using a 12” square 2 “ thick fire brick/ paver layed on Cadillac board with dome on top of floor??

Tight as possible, preferably at a diagonal to the front entrance. No mortar under or between them. It's important to get them as flat as possible. Your peels will thank you later.

[UtahBeehiver]

Agree, after the floor is laid you can knock off any high spots with an angle grinder and a diamond cupped wheel.

[P3 Stoaker]

G'day All,
Russell and NCMan, Thanks will do. I probably should have added why I asked, which was a post somewhere saying to leave a small gap for expansion movement. Anyway I'll lay tight. Thanks
One other last check for anyone's opinion before I'm fully committed. And yes it's about the tapered arch, sorry but just wish to confirm, not sure if I'm stupid or cautious, hopefully the latter !!!
Photo 1 and 2 show where I plan to have the lowest inner arch bricks in relation to the extended dome arcs. Photo 3 it with the IT tool set at length and looks ok on the TDC I believe ?? My question is how do I know what the height of the dome will be there at the top where it intersects the arch ?? Photo 4 shows the IT a little lower which doesn't look right. How do I know the dome won't intersect at that height which seems too low?
I have attempted to measure/predict height but I've not found reference to doing that here on the forum and guess most don't do that ??
A huge thanks for all the advice so far. I live in the famous Barossa wine region north of Adelaide in South Australia. Come and visit and I'll show you around !
Regards

[NCMan]

G'day All,
Russell and NCMan, Thanks will do. I probably should have added why I asked, which was a post somewhere saying to leave a small gap for expansion movement. Anyway I'll lay tight. Thanks
One other last check for anyone's opinion before I'm fully committed. And yes it's about the tapered arch, sorry but just wish to confirm, not sure if I'm stupid or cautious, hopefully the latter !!!
Photo 1 and 2 show where I plan to have the lowest inner arch bricks in relation to the extended dome arcs. Photo 3 it with the IT tool set at length and looks ok on the TDC I believe ?? My question is how do I know what the height of the dome will be there at the top where it intersects the arch ?? Photo 4 shows the IT a little lower which doesn't look right. How do I know the dome won't intersect at that height which seems too low?
I have attempted to measure/predict height but I've not found reference to doing that here on the forum and guess most don't do that ??
A huge thanks for all the advice so far. I live in the famous Barossa wine region north of Adelaide in South Australia. Come and visit and I'll show you around !
Regards

I think where the confusion may be is that a small gap around the edges for expansion is recommended, if placing the floor inside the brick walls. However, for the floor itself, yes, lay them tight. Sorry for the possible confusion on that.

[UtahBeehiver]

The dome will be there as long as you follow the IT. I cannot see how the IT will be set on the other end, The pivot point should be a floor elevation. The first brick at the base needs to be cut to follow the ID of the dome but the placement fore and aft is correct once you cut the arch shape. The top dead center of the tapered arch is where you start the work you way right and left of TDC. Note the cuts will be skewed and each one different so do NOT cut them all the same. Lay the the TDC brick with the IT. Then looking towards the inside of the dome, the next brick left of TDC, the right side of this brick will have the same angles and slopes of the left side of the TDC brick, then mark the left side of the new left brick of TDC with the IT and connect the dots, then repeat the process with the second brick left of TDC and so on and so on. Repeat the opposite process with the bricks right of TDC. The light bulb will click on.

As mention by NC the only gap on the floor is the a cardboard thickness between dome wall and floor if the floor is "cut to fit inside" dome, this gap is not filled in with any mortar, ash will eventually fill in.

[JRPizza]

I have a question about placement of your arch form. I found it much easier to calculate how far forward I wanted my arch and set my arch form with the front edge at that point and made sure it was perpendicular to the base. That allowed me to index all my bricks with the forward edge flush and helped keep the arch aligned. It appears you have your form set back and I was wondering if that was done for a reason?
Also about your placement - in your third pic I can see where the IT bracket sits in relationship to the TDC brick, but you need to check where a brick nested in that bracket will sit on top of the TDC brick. You can see in the attached pic that my arch is placed so the brick in the IT has enough rearward projection (to the left) to have the inner radius cut on the lower half and an angle for the topping dome brick on top. Ignore the line drawn on the upper right it was obviously not used.

[JRPizza]

Here is a few sketches of where the arch bricks should be placed to properly intersect the dome.

[UtahBeehiver]

JR is right, I overlooked where the bottom of the arch form sits, The bottom part of the inside of the arch form needs to sit on the ID arc of the dome. You also need to include at least 1/2" of release on the arch form to be able to get the form out after the arch is done. Also save the arch form as a template for you oven door.

[P3 Stoaker]

G'day All,
Many thanks for taking the time to reply. I 'think' the position I have will be ok but there are a few points you have raised I didn't quite get.
For info I plan to have quite a low entry, 42 and half inch dome ( adjusted metric) with a 270 mm (10 and 5/8 inch) inner arch opening height. That might be why my IT to TDC angle looks a little lower than most.
NCMan, All good, thanks I'll lay tight-ish.
Russell, My IT pivot is very close to correct in last post photo's but I will be modifying the lower mount ( fork bolt) to be even better. You mention 'The dome will be there as long as you follow the IT'. An important aspect, I've been wondering how high or low to position the IT on that TDC brick to mark and cut. I think its more about mark and cut that TDC at a reasonable position and the dome will be there. Would you agree the height of the IT where you mark TDC is mainly about having enough brick cut to meet the dome course above and a little below to cut the lowest inner corner off ? In your reply you say 'The bottom part of the inside of the arch form needs to sit on the ID arc of the dome' . I don't understand why that is and I'm wondering what I'm missing??
JRPizza, The form I made isn't all that wide and therefore cannot be positioned in line with the outer edge of the arch or the bricks will fall off. I planned to measure the outer edge of the bricks to the outer edge of form to keep vertically aligned, do you see problems? I think I get what saying in the next paragraph. Would you agree in my photo 3 the short side of the IT 90 deg piece of angle could be used where it is to mark the inner radius, and looks ok to me ?? A brick nested in the it would have a little steeper angle, but even as it sits it seems reasonable to me ???. I think you were saying the TDC needs to be 'IN' far enough to have a good cut face on top to intersect dome and also enough to cut the little corner off, lowest inner corner?? As far as I can determine my position in photo 3 will achieve this ?? Till now I've been wondering how high/low to position the IT and mark the TDC but I now see it more as you mention, balance the cut as described above. In your sketch 2 it appears as if a line drawn across the front edge of the lowest arch bricks would go very close to the outer radius. In sketch 1 the TDC outer edge appears closer to the inner radius. Am I seeing this correctly?

I'm going out to dry build the arch again. Certainly appreciate the feedback and I owe you guys big time.
Regards
Greg

[JRPizza]

I hope you have done some research and found evidence that a ~50% door to dome ratio opening will support a good fire and draft. The recommendation for an "ideal" ratio is 63% and there is some leeway on each side. Would hate for you to build something that did not perform up to expectation, but having said that I have no idea if it has been done and how one would work. Is there a reason you want such a low door? Most that build low do so because they have a small oven or a low dome style. My 39" had a 12.25 height and I have to take the lid off some of my favorite pots to clear the opening.
Regarding your arch, you might want to consider adding a little thickness, maybe another piece of ply to the rear of your form so you don't have to measure, but that is up to you. It "looks" like you have the TDC brick placed properly, but can't tell without a shot like I did in post #37 above. Once you are confident the arch is properly located, I would also recommend not trying to cut all the bricks at once but rather cut and mortar as you go. You can see I did this in the pic below where even though I had made marks on my TDC brick as shown above, I did not cut the TDC brick until the bricks on each side were cut and secured. I also attached one to show how the outer dome line was cut and the brick topping the TDC looked in the IT.

[P3 Stoaker]

Thanks JRPizza I appreciate your comments.
On the dome and opening. I've done a lot of reading on the forum to gather info and the place where I'm buying my refractory bricks, well he, Glen builds lots of brick ovens for a living. I certainly respect and welcome all information but eventually as I'm sure you experienced, you have to peg in and go one way or another. Glen definitely believes the go for a 42" , metric is around 42.5 to actually flatten the top of the dome off a little, to around 500 mm (19 and 11/16") and the opening 270 mm (10 and 5/8'). Is it better, who knows but it's about 54%. Will it work well, I do expect so given he's built many. My thoughts were the slightly lower dome probably can't degrade performance, and the lower arch, with my limited experience, probably shouldn't either, still plenty of opening for air to get in. One thing Glen did say was the fire is best on one side of the dome, not at the back. This means the cool air is drawn in to the side where the fire is. Whether his set up effects this balance and requires a side fire, who knows. Where do most people have the fire within the dome?
It is hard as I respect info here on the forum and from Glen. This has however made it a little tricky as I do not wish to offend or seem unappreciative.
Has anyone reading built a somewhat lower dome and lower inner arch? How did it perform?
Regards

[UtahBeehiver]

Not sure who Glen is but we first need to verify exactly what type of oven is being build is it a pompeii (high dome) or a neopolitan (low dome). The door height ratios change based on oven type, IE high dome runs about 63-65% of dome height, where as low dome for a 42" base OD with dome height 15.5" is 11". But it is your oven so you need to do what you need to do. Perhaps you should focus on the other persons recommendations rather than a mix of this forum and the other so you don't get a hybrid of designs that won't work for you.

[JRPizza]

Russell is right - you need to pick a design and move forward with it. "Most" of the ovens built on this forum are Tuscan type and they work well when the general rules are followed, so that is the lion share of the recommendations you are going to hear. The high hemispherical dome is easy to build once you have a proper IT and a semi-circular arch mates well with it.
Just tell us what you need and we can try to help.
If you are going to follow Glen's advise get a feel for how much help he is willing to give you, as you may run into some geometry specific questions that we might not be able to help with.

One last shot at the "ideal" ratio. When I was researching ovens I saw multiple references to 63% being the ideal height, and one of those was a book "Bread Ovens of Quebec". I attached a link to a download at the bottom and an excerpt from page 38 that discusses what the author's called "index of circulation"

Of all these considerations, shape is the most important, since in the material culture, as Henry Glassie115 so ably demonstrated, this is the most traditional characteristic; it remains the same from one place to another and from one period to the next. Thus, the inner shape of the dome always increases gradually in height, from the door to the rear of the oven. However, this elevation should be moderate, neither too high nor too low in relation to the size of the opening, so as to permit good hot-air circulation in the oven; Diderot pointed this out in his Encyclope'die. We wanted to check the variability of this factor in the ovens constructed in Quebec. In order to do so, we calculated what we shall call the index of circulation, using the information in our technical data, which gave the exact external and internal dimensions of the ovens. Taking the maximum internal height of the dome as 100, this index represents the part of the dome that rises above the height of the opening. It is obtained by the following formula: x loo internal height of the dome - height of the opening internal height of the dome In this way we found that the average index of circulation in all the ovens we examined was 37. In other words, the average oven had a dome measuring 100 units in height and an opening measuring 63Of all these considerations, shape is the most important, since in the material culture, as Henry Glassie115 so ably demonstrated, this is the most traditional characteristic; it remains the same from one place to another and from one period to the next. Thus, the inner shape of the dome always increases gradually in height, from the door to the rear of the oven. However, this elevation should be moderate, neither too high nor too low in relation to the size of the opening, so as to permit good hot-air circulation in the oven; Diderot pointed this out in his Encyclope'die. We wanted to check the variability of this factor in the ovens constructed in Quebec. In order to do so, we calculated what we shall call the index of circulation, using the information in our technical data, which gave the exact external and internal dimensions of the ovens. Taking the maximum internal height of the dome as 100, this index represents the part of the dome that rises above the height of the opening. It is obtained by the following formula: x loo internal height of the dome - height of the opening internal height of the dome In this way we found that the average index of circulation in all the ovens we examined was 37. In other words, the average oven had a dome measuring 100 units in height and an opening measuring 63

http://heatkit.com/docs/Bread%20Ovens%20of%20Quebec.pdf

[GreenViews]

Hey Greg, looks like you are coming along! I am also doing a low dome and had to take a few days with little work on it, but just uploaded some new pics on my page with discussion on how I'm planning on my IT and build. I've seen others with a different complex IT design. My dome center of radius is below my floor, so it just takes a slightly more complex IT. Re: door height, I have no experience whatsoever to bear, but I decided to go with what the recommendation was in the FB design book v2.0. I just did paper sketches to a scale of top down and side profile to look at how my inner arch interacted with my dome profile. I found that I needed to move my door into my oven a bit and use 6" length of brick to be sure I had a stable arch that intersects my dome well along the profile and at the top. I will cut some of the front off of these brick as needed. I can share more how this goes soon. I've also read other sources, one of which was a study of Canadian clay ovens where they looked at performance vs opening/dome ratio and it is important. (possibly this one the same original source JR referencing above?) All these point to about 63% plus or minus a bit. Too high a dome compared to door arch can lead to cold spots in dome from inefficient airflow or eddies apparently. Best wishes... I'll keep following and learning!