42" Pompeii construction in Adelaide

[GreenViews]

Hey Greg,

It looks to me like you did your homework on the door arch meeting the dome. I would also look at slightly lower elevations in the arch to be sure they don't move back from your dome. This would depend on the shape of your door arch and I don't remember if you said what your plan was. I did a segmental arch which worked well with the shape of my dome. Many people do a rounded or semi-circle I believe.

Related to this and your question of the template. If you are doing a rounded arch: start on a piece of plywood and mark your door sides and the very top of your door. Next mark the centerline of your door and measure down from the door height mark: measure half the width of your door and make a mark at that point. Then you use a something to make a semi-circle from that centerpoint you marked from one of the walls to the top of your door then continue in the circle to the other wall. Above where this semi-circle meets the wall is your template cutout for the top of the door and bottom of your arch, below where the semi-circle meets the wall will be straight wall to the floor of your oven.

If you are doing a segmented arch, the process would be similar, but you would choose the center of your arch according to how flat or rounded you want the top of your door to be. I personally had it roughly figured out then waited to finish my template until I went up 3 bricks, then calculated the center of my segmental arch based on the radius needed to meet the actual height of my wall to the desired height of my doorway.

Can't help with the other questions, although I was told a regular tile thickness is sufficient. I actually had other used tiles at the ready, then seen pic (if I remember correct) of your mosaic tiles, then went to a Habitat Restore (used building supplies supporting Habitat for Humanity) and bought some of the same like I saw cause I though.. lots of room for the water to run off and out. If water accumulates higher than that, I'd imagine I'd have greater problems that need resolving, but I have no real world experience. Looks like your plans are coming alone quite well. Can't wait to see it take shape! Cheers Tom

[P3 Stoaker]

G'day All, thanks for the feedback.
Greenviews, thanks for the reply, I appreciate your comments, and yes acknowledge regarding questions.
JRPizza, Thanks for the reply. I'm going down the more traditional high dome dimensions, full even arc dome but with a slightly lower entry. Slow progress with lots going on but I'll get there.

Regards
Greg

[JRPizza]

So, did you all have a look at the Quebec oven document? The authors were doing a little "reverse engineering" looking at door to dome ratio. They noticed that some ovens had supplemental "holes" in the oven which they speculated were added because the draw was not proper. I attached a screen shot of their graph. They use a ratio of 1-(door/dome) for some reason, so a 63% ratio is 37 on the graph. We used to say at work that very small deviations from spec are usually not harmful, but we rarely knew at what deviation the performance would be seriously effected. That is where my knowledge of opening height is For what it is worth, the concept of a performance drop as a function of deviation from nominal is called a Taguchi loss function (for those that like to nerd out https://en.wikipedia.org/wiki/Taguchi_loss_function)

[GreenViews]

Just found the option for viewing conversation by latest activity first... in the User settings page select Latest activity... I then noticed this is a toggle on the top left of all "conversations" so you can switch back and forth easily regardless of your default.

[GreenViews]

Hey Greg, I love your new space. Going to be beautiful!

Been doing some thinking on your question about door height and no further answers from others. I think JR and Utah probably feel they already answered. I went back and looked JR gave example of his latest build and I went back to his build thread there to review. His Pompeii (high dome) was 39" build, so presumably 19.5" dome height and he used a 12.25" door, so 62.8%. JR also shared other research saying 63% is the key. Utah then shared 63 to 65% door height for high dome and slightly different for low dome. I'm guessing they feel they have given what they can from their knowledge and experience. Might have to look for posts from others who used a different ratio to see their experience???

First dome course: I was instructed twice to not mortar the first dome course, but to lay it down with a 1:1 sand:fireclay mix. They say it needs to be free to move slightly.

Specific questions: I do see others starting a new thread in the appropriate place in the forum if they do not find their question answered after searching the forum. That might be a way for others to see your question who are not following your build.

Order of posts: Wow, good question! I've been either typing the number of last page in at the top of a thread or going to the bottom and selecting the last page. I just looked and also didn't find this option.

[P3 Stoaker]

G'day All,
Greenviews I have included a few pictures of our pergola area progress, pizza oven just outside the end and open fire along the side, which will be panelled up. In hindsight I probably would have had the oven under cover but the area was planned before that thought and extending the pergola past 6m (20feet) was a lot bigger task structurally.
Can anyone tell me, can we see posts where the newest page displays first? I can't find an option for that, will save selecting through every page of one's own build every time and I'm sure there must be a way given some members have 20 or 30 pages ??
Build questions, should the first dome course be mortared to the oven floor bricks?
I'm never sure whether to repeat a question swamped by several posts after asking a question if not answered?? To be answered readers would need to track back several posts, should I just repeat questions in that case?
On that subject I was chasing thoughts as discussed in post #46, any thoughts/comments would be greatly appreciated.
Regards

[GreenViews]

Yeah, FB guide recommends 12.5" opening height and 21" high dome for your 42" round high vault style. I also hope others can verify that is good in their experience. My reason for low dome: I simply read somewhere that it made better Pizza. I later read opinions that the difference is minimal and low dome uses more wood, but I'm committed now.

[P3 Stoaker]

G'day All,
Greenviews, sounds like you are progressing well. The 9.75 inch opening is lower than I was initially thinking, by around 1". And your dome is almost 5" lower. Certainly makes the IT tool design interesting but by the sounds of it you have that sorted. Out of interest why are you going low dome?
I've decided to stay safe and keep to more traditional dimentions, although I am considering a slighly lower entry, at around 55%. I'll be more comfortable moving forward with those dimentions if I can lure the thoughts from a few of the wise and experienced members, hence my question in the previous post. I hope to get some feedback regarding that.
My oven is going just outside a pergola which is also under construction and includes an open fire. The framing was completed today and the heater is in place awaiting some panelling and render. So has kept me busy awaiting info regarding the pizza oven design. I'll post a few pics tomorrow.
Regards

[GreenViews]

Greg, Seems like a good question to me. The FB guild v 2.0 gives the following guidance which calculates to 60% for high vault and 71% for low vault 42". That is within a few percentage of the 63-68% widely recommended. Mine is a 36" low build so their recommended door is 69%. Personally, I was tweaking my build to go 9.75" door and 15" dome for a 65% ratio, which is closer to the 63%. I'd love to hear others weigh in as I have no real world results yet. p.s. just posted video of my second course going in!

[P3 Stoaker]

G'day All,
I've had a think about the way forward, and to be honest whilst I remained concerned about moving forward on the advice of 1 person, the endless experience on this Forum is something I've found super helpful to the point that I've decided to go ahead with a more traditional build. Thanks Russell, as you say if I mix it up things could get complicated, I'm not a gambler and thanks JRPizza, if it's not broken why try and fix it and there is less risk going traditional.
So I'll probably stay with the 42.5 Inch. I've read many posts and a few have recommended for the 42, a 12" tall by 19" wide opening, however this around 55%. Lots of posts say around 62-63% or a little either side. Would appreciate thoughts as to whether 55% is within reason ??
Regards

[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!

[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

[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.

[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

[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.