40” Pompeii in Rhode Island

[NewEnglandNewb]

To squirrel tail or not?

Background: My wife has a friend whose husband built a wood fired oven a few years ago. It is a Pompeii style and I think he followed the forno bravo plans. It has an exposed rendered dome. That is what my wife was expecting our wood fired oven to look like. We were discussing how I was going to finish it the other day. I was explaining how I was going to build an enclosure and explained the squirrel tail chimney and how the chimney would exit at the peak of a conical roof. She isn’t a fan of how tall the roof would need to be and was asking if I could make it shorter.

I’m going to build a round enclosure with a conical roof either way, but it did get me thinking about doing a more traditional vertical flue/chimney. I could then keep the roof closer to the dome of the oven. I figure that could reduce the height of the roof by at least 12”. I think this would also simplify the build a bit.

If I do a squirrel tail over the dome, my plan is to insulate between the dome and the chimney for better retained heat cooking. I was thinking of using P/V Crete to create a level surface between the flue and where the chimney will exit over the dome. Put down a layer of calcium silicate board (I bought an extra sheet for this purpose), then use a 8x12 clay flue liner.

So, what would the forno bravo community do? Vertical chimney or squirrel tail?

[NewEnglandNewb]

Thanks Mongo! That is comforting coming from you as your build is one of my favorites on this forum. I actually went and reviewed your description of how to cut the backside of the arch bricks right before I did it. I didn’t take a picture, but I had a bunch of extra threaded rod. I unscrewed my IT from the turnbuckle and screwed in a length of threaded rod that was long enough to extend past the far side of the brick. Then I threaded two nuts onto the rod that were located where the two yellow dots are in your picture below. I used that to one by one mark where to cut the arch bricks. That method worked well.

[mongota]

"I do wish I was a little more careful keeping the mortar joints consistent in width."

The interweb isn't big enough for me to list all the things I fretted over during my build. In the end? My oven as a whole looks pretty darn bueno, even after all these years. And it still cooks a great meal.

Be contemplative in your build, do the best you can without getting dragged down and stuck in the weeds. The things that are uglies to you, I pretty much guarantee 98% of the people out there won't even notice. Because they're not uglies, they're just not how you pictured it during the build. To me, your arch looks terrific because the work is neat and I have no preconceived notions of how YOUR arch should look. Regardless, the 2% that notice an ugly and point it out to you? They're just jealous!

[NewEnglandNewb]

So I decided to take the easy way for the arch and just bought arch firebricks. The angle isn’t quit steep enough to have even mortar joints, but I figured there will be very little inner arch showing and none of the outer arch (I plan on covering that with a decorative arch). I do wish I was a little more careful keeping the mortar joints consistent in width. I pulled the arch form down the next day to clean up the excess mortar before it had a chance to dry too solid. I’m happy with how well it cleaned up.

[UtahBeehiver]

That is probably a one of the reasons to save on the diamond blades. I ended up using about a baker's dozen my super duty brick. If you are able to make the jig work with no issues and the tolerances you are after, that is great too. FYI, it is much easier to tie into the tapered inner arch then to tie into the dome with the arch not there. Suggest at least keep the arch ahead of the dome courses.

[NewEnglandNewb]

I appreciate the feedback guys!

david s, I do have weep holes both under the floor and under the dome insulation. I saw your advise to Daiden in his Neapolitan build thread and incorporated it when I poured the hearth.

UtahBeehiver, I’m curious, is that your recommendation because it took so long to cut the high duty bricks you used? It only took about an hour to make that jig. Cutting the bricks goes really smoothly once I get the bevel angle dialed in, which I think would be the same effort either way.

I finished the fourth row and started the fifth row so there is something solid to push up against when I get back at it (per Russel’s recommendation). I ended up deciding to take it this far before tackling the inner arch since it will be much more stable to lay out the arch bricks when the sides are supported.

[david s]

On weep holes, as well as assisting the removal of moisture under the floor, if more are placed under the dome insulation the pressure build up of steam in the dome insulating space can also help drive out moisture as it accumulates there, moisture travelling away from the heat as it finds its way to the inside face of the cooler outer shell where it re-condenses. (the drawing explains how this works).

On tight brick joints Daniel Rhodes, the author of Kilns (considered the kiln builders bible) has this to say.
”In kiln building it is much better to have a loose structure than a tight one. For this reason the amateur may have a slight advantage over the professional mason, because his bricklaying is apt to be somewhat loose and not tightly locked together. I have seen kilns made by professional bricklayers which in use suffered severe cracking and swelling due to the overly tight and precise workmanship and the lack of expansion joints.” Kilns experience around double the temperature and thermal expansion to that of an oven, but the same principles apply.

Some discussion on this topic here.

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/456627-refractory-mortars#post456627

[UtahBeehiver]

No one will ever know the difference in brick batches. They will be more interested in the flames and the pizzas that come out. Plus the inside of the oven will carbon over until you reach 700 F and the oven clears. FYI, I was like you and had to have tight joints from the ID to the OD. If I do it again, one only has the bevel the first 1 inch or so of the ID brick to correct the inverted Y then use your homebrew to back fill the back gaps. JR Pizza used this method, you get tight inside joints and the let mortar be you friend and use your labor resource for other parts of the build. No one sees the OD of the brick dome since it is covered with insulation and final dome covering.

[NewEnglandNewb]

Slow and steady progress. I’m sure I’m not the only one here who thinks they should be able to get more done in a day than what actually happens.

I was able to get two rows in before there was a noticeable inverted V starting to form. I made a jig out of a cheap plastic cutting board to be able to cut the angle and bevel on the bricks in one cut. I’m using home brew mortar, 3,1,1,1 sand Portland cement, hydrated lyme, fire clay.

I ended up taking two trips to the refractory supply place to get all of the fire bricks I needed since they didn’t have enough the first time. I knew that heading up the first time, since that would have been ~800 lbs over the payload capacity of my SUV two trips seemed wise. It turns out that Mt. Savage has three different factories that manufacture their bricks. The two batches of bricks I got look somewhat different. If you look closely at the picture below, the first row came from the first batch, the second row came from the second batch. They supposedly have the same material composition, so I think I must just be a difference of the aggregate used. I have enough of the first batch to complete the outer arch and floor in the landing and enough of the second batch to build the rest of the dome, so that is my plan. I’m probably the only one who will ever notice this difference, but had I known I probably would have held off until the refractory supply place had enough for my whole build from one batch.

[mongota]

Looking good!

[UtahBeehiver]

1/8" joints are a great target but you have some wiggle room to work with too. There is a tool called the Angleizer by General Tool that will help you set up the Ax arch and it use to have a program with it that spit our top and bottom dimesions of the wedge shape of the brick. I still have the files, not sure they still work but if you PM your email I will send them too you. The tapered arch whether Ax arch or full arch use the same concept as shown in the first pic. You start with the Top Dead Center brick (you need to use full size bricks in order to cut the taper) then work down each side "ONE" at a time, using the last brick to mark side near the previous brick then the IT to set the opposite side of the brick. You cannot cut all at once, since the angles change as you move down either side of the TDC.

[NewEnglandNewb]

I am planning a tapered inner arch. It will look more like the second picture than the third as I’m not planning on it being circular. Having the vertical sides seems like it will give a little more room for pulling pots in and out of the oven and that style of arch will match the arches in the stand.

I grabbed some 1/8” plastic shims to help space the bricks out to simulate the mortar joints. Are 1/8” joints a reasonable target for home brew mortar?

[UtahBeehiver]

Are you going to do a tapered inner arch? It is well worth the effort and makes the dome/arch interface easier. It is one of the more difficult concepts to visualize but worth considering.

[NewEnglandNewb]

I set the pump for the wet saw up in a separate bucket like Russell suggested. This setup worked great! I got the floor cutout, then wrapped the edge with corrugated cardboard to keep a gap between the floor and the dome to allow them to expand/contract independently when heat cycling. I’m hoping to get the inner arch and a few dome courses laid out and cut tomorrow. One of the local building supply places has everything I need to make home brew, I will pick up those supplies this week.

[NewEnglandNewb]

Thanks Russell, I will grab a longer hose for the pump and give that a try over the weekend.

i made my IT and started playing with it to lay out the oven floor. It is screwed to a piece of melamine covered MDF that is cut to be the same shape as a brick. It was the perfect thickness for the pivot to be level with the floor. The IT length is adjustable from a little over 20” to a little under 18”. I do plan on reducing the radius of the dome a little as I go up, with the goal of having an 18” ceiling height. I also cut a grove into the block the inner face of the brick rests against to hold a pencil even with that face. That made it easy to draw the circle on the floor and should come in handy laying out the inside face of the inner arch.