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pizza_bob 07-03-2009 05:05 AM

Pizza Bob's 42" Build
4 Attachment(s)
I probably should have started my build thread earlier but better late than never...

I'm building a 42" Pompeii style oven. I'm a mechanical/design engineer (mostly medical instruments for surgery) and have never "buttered" a brick before. But I am Italian and must have it in my blood.:D I have recently become a first time father with the birth of my son Luciano. I'm a triplet (three boys) and 6'6" tall - so yes my cooking hearth will be approximately 50" :eek:

I have been obsessed with creating this design in my CAD software (SolidWorks) before I do anything outside. I am pouring my insulation layer today so I've been trying to stay one-step ahead on the computer design. I started laying-out the vent landing area and was looking for some advice.
I have been viewing exceloven's images to get sizes of certain areas of the oven by counting bricks. Has there been any advantages or disadvantages of having a 13.5 vent landing depth? The images below show a that depth and a vent opening that is 16.5" x 4.5". Will a vent opening of this size create too much ofa draw and contribute to problems retaining heat?
I thought exceloven's method of creating the "hard stop" for a door was great! I think I laid it out the same way. It ends-up being a 1" reveal that is created by offsetting the inner arch - very clean looking.
My hearth "sandwich" is 3.5" structural concrete w/rebar, 2.5" Foamglas under the oven and vent landing area, 4.5" of vermicrete at a ratio of 4:1 to provide some thermal mass and then the cooking floor bricks.

I look forward to the rest of this build and discussions with all in the group. I would never had been able to do this without this group.

Thank you in advance!


DrakeRemoray 07-03-2009 08:23 AM

Re: Pizza Bob's 42" Build
My vent landing area is approx 15" deep and 19" wide with a cast vent over the entire area. It collects smoke very well and there is no issue with it retaining heat as better air flow just means more fire when the door is off and when the door is on, the vent area is no longer in play (the vent is in front of the door). If you do make a deeper landing as you have shown, why not make a larger smoke collection area to match (make the hole at the top of the arch deeper), it will end up meaning less smoke out the front, but it will probably make the vent arch to chimney a little more complicated.

Also for the insulating layer, is 4:1 less than the recommended mix? (it has been a long time since I built mine). You want that layer to be insulation only, not mass. If you want to add extra mass, do it in the dome.


Dino_Pizza 07-03-2009 08:39 AM

Re: Pizza Bob's 42" Build
Congratulations Bob, your off to a great start. I like your Solid Works renderings. Your design is solid. You should be able to build it exactly as you have sketched. You can and probably will make a few tweaks along the way.

Is this a 42" oven? I think Marks-exceloven vent opening is just over a half brick deep. Many have vent openings your size but move the outer arch another inch out & you increase the vent by 25%. That's always a good thing. You certainly don't have too big of an opening. Good draw creates good heat. Also, the nice deep landing you have is great but again, I think form looking at Marks pics, his landing flairs slightly which makes it easier to get your door against the nice hard-stop your creating. He'll probably confirm that soon. Maybe you plan on doing that but it's a bit hard to draw in cad.

IMHO: your vent opening is great if you're casting a custom vent or using a clay flu pipe cut and tapered so you have a smooth transition. If you go with an 8" duravent, then a more "squarish" opening would make it easier to transition but make cutting bricks tricky around the vent anchor plate.

I've got a 15" landing and my opening grows 3.5" at the outer arch and it's just great. You don't get any "cave" feeling into the oven and it feels "roomy".

Planning ahead is a good thing and you've a good handle on it. Please post some pics of the insulating layer too. Thanks, Dino

Lars 07-03-2009 09:15 AM

Re: Pizza Bob's 42" Build
Hi Bob,
Well, I am not done with my oven yet, but I will cast my 2 cents here anyway.

I would recommend making your vent area wider. I did what you have drawn ( essentially) and I am regretting already the smoke out the front of my 39" oven during curing. Also, the low arches were a slight problem for me. Not only did they need buttressing, but when they heat up ( you can see my crack thread) the arches all developed cracks.

I would definitely recommend making your smoke vent extend all the way across the arch area. You can then fill in the sides with triangle bricks to give your vent a taper going smaller/up... and meet up with your flue. I WISH someone had told me this when they were looking at my 'flue design' in tools, tips, techniques,etc. In fact... right now I am going to go edit that thread myself!

One think your drawing does not show, that I am very happy with ( that I did throughout my dome) is tapering each half-brick. ( I show how I did this in a 'tips, tools, techniques' thread called 'Tapering Bricks with a chisel') I really liked the way the pieces went together with an 11 degree angle.

pizza_bob 07-03-2009 06:20 PM

Re: Pizza Bob's 42" Build
1 Attachment(s)
It seems as if I will go with a larger vent opening. I have the room for it. I was just concerned about losing too much heat up the flue but that doesn't appear to be a shared concern - which is good.
How tall are your arches? Did you use the same mortar that was used on the dome for the arches? My oven opening is 12.5" and the arches in front of the oven opening are 13.5". The width of the oven opening is 20" and then 22" wide in the landing area. The landing area height and width is one inch larger than at the oven opening because of the one inch reveal left for the door.

Yes, this is a 42" (internal) oven. I like your idea of tapering out or flairing the landing area. I did not plan to do that but I agree that it will simplify putting a door in place and get rid of the "tunnel" or "cave" feeling. My question is...Did you have difficulties building the arches in this tapered section? Did you have to taper the buttress bricks (the base of the arches). I know they need to have an angle on them but how did you account for the taper in the longer direction? I'm not ure if I'm explaining it correctly so please forgive me.

Yes 4:1 vermicrete ratio is less than the FB specified 6:1. My thought was to try to lean towards a little more thermal mass than insulation. I thought I would need some thermal mass under the cooking hearth but not too much. The oven will be primarily for pizza but I'm worried about the hearth needing to be "recharged" after a few pizzas. It's a crazy insulation-thermal mass balancing act that I have been driving myself crazy over the past few months! Do you think the extra mass in the dome will help keep the cooking hearth charged for multiple pizzas?

I attached a picture of the Foamglas that I installed today. The Foamglas is 2.5" thick and placed on the structural concrete layer. When I poured the structural concrete layer my plans were to do a 4" layer of vermicrete so I did not smooth/level the top as well as I should have for Foamglas. So today I put down a thin coat of Quikrete mortar as a scratch-coat to set the Foamglas on. Tomorrow I will pour the a 4.5" layer of vermicrete over and around (encapsulate) the Foamglass. The 4.5" vermicrete will only be 2" on top of the Foamglas but 4.5" from the structural concrete layer.

Thanks everyone for the advice - keep it coming! :D

Best Regards,

dmun 07-03-2009 08:13 PM

Re: Pizza Bob's 42" Build
It's black? Huh. Let us know how the foamglas works out. How does it cut? Is it flat on the surface?

DrakeRemoray 07-03-2009 08:24 PM

Re: Pizza Bob's 42" Build
Hey Bob, I don't know what the foamglas is. Is it insulation?

But to answer your question. The mass of the dome does not really recharge the floor, the active burning fire recharges the floor. We often have the debate about adding extra mass. It is just not needed for making pizza. The commercial pizza ovens that James sells on this site have floors thinner than a firebrick. I added an inch of mass in the dome in order to bake (see some of my threads, I have killed myself trying to use all the heat the oven retains, and I often wait for hours for the oven to cool enough to bake in it.

We really recommend insulating under the floor, and I just am not sure that the 4:1 mix would be sufficient. Once the oven dome is completed, it is virtually impossible to go back and correct that mistake.

My two cents.


Dino_Pizza 07-03-2009 10:14 PM

Re: Pizza Bob's 42" Build
2 Attachment(s)
Bob, great questions, I hope we are not overwhelming you with design thoughts and and our own question but this all will make for a great WFO build. I think I understand what you are asking. Yes & no: Yes the tapering of the "arch wall shoulder" was difficult. No, the tapering of the arch bricks due to the flaired opening is not difficult at all. It kind of just happens. My arch walls are built 3 bricks high plus the triangular "shoulder" brick that starts the arch. Many others (most?) have 4 bricks high like your drawing so your opening is less "archy" than mine. I think the shallow arch (4 brick high walls) puts a tad more pressure on the vent walls and sometimes needs butressing. 3 bricks and an archier curve, even with the flaired opening just didn't seem to warrant butressing.
After cutting your floor bricks, soldier course, a few rings, you will be amazed at how easy or intuative the tappers come to you for the arch and vent wall area. You'll be surprised at how much 1/4" of mortar on each side of your vent will bring your flaired arch back to "square". Here are 2 pics of my vent walls and arch walls and I did waste $4-5 in bricks on those "triangular" and tappered arch bricks at the curves, but it was worth it and easy in hind-sight. Keep up the good work, Dino

pizza_bob 07-04-2009 06:16 PM

Re: Pizza Bob's 42" Build
5 Attachment(s)
No, you are not overwhelming me with design thoughts - it's what I do every day for work too! :D Thank you for all your help. I agree with you about the "archier curves". I changed my layout as shown in the image below. I will taper my entry too but don't think I need to do it in SolidWorks - I might but haven't yet. Did you use 1/2 bricks for the inner arch(es)?

Yes, the Foamglas is black and, well, like a block of glass. When rubbed against the concrete it comes off like powder. It's very abrasive - it reminds a lot of hard pumice stone. You will notice the attached picture that the corners were not perfectly square. Rather they are kinda' rounded over. This was due to poor handling when shipped to me. I have seen pieces that had crisp edges and corners. It's all how they package it. The blocks come in 24" x 18" and the thickness range is 2" to 6" (1/2" increments). I went with 2.5", mortared (thin layer) it to the structural concrete layer and today I FINALLY poured the vermicrete layer!! I did not have to cut this but understand that it does wear down a skill saw blade quickly. I wore a mask whenever handling this stuff because of the fine glass particles.

Did I tell you I FINALLY poured my vermicrete layer??? I followed cvduke's method of mixing the Portland in a five gallon bucket with water until it was like a slurry. I used the paint mixer that I picked-up at a paint store of $4.00. It mounted to a drill and worked like a charm! I had the vermiculite in a wheel-barrow and uniformly moistened it with water. Then I poured the Portland slurry in the wheel-barrow and mixed it uniformly with the vermiculite. I used a pitch-fork which seemed to work really well. I went through approximately 8 cubic feet of dry vermiculite and a 90lbs bag of Portland cement. The form I built for the vermicrete layer was approximately 9 cubic feet and then minus 3.5 cubic feet of Foamglas left me with a volume of 5.5 cubic feet to fill with vermicrete. I'm not sure why it took 8 cubic feet of dry vermiculite to do this but it looked like the correct consistency and it seems to setting just fine 8 hours later. It was so tempting to use the cement mixer which was right next to me but I held back. I went with a 5:1 ratio. I did this because I wanted to lean slightly towards a little more thermal mass. I realize this shouldn't be used as thermal mass but 5:1 must provide a smidge more thermal mass than 6:1 - Correct?? I didn't do this without any thought :rolleyes:. My thinking was that the Foamglas is a superior insulator compared to vermicrete. Since I have 2.5" of this "superior" insulation I should be able to lean the vermicrete towards a little extra thermal mass. I let you know how it works...

Did I tell you I FINALLY poured my vermicrete layer?? Sorry for repeating this but I'm excited to start my dome!

Best Regards,

pizza_bob 07-04-2009 06:21 PM

Re: Pizza Bob's 42" Build
3 Attachment(s)
Sorry...I had three more pictures I wanted to upload. :cool:

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