39" (100cm) Pompei Oven Build in Belgium

[Kvanbael]

(This is a repost from last week. The original got lost in the recent forum backup restore)

It was really nice weather this weekend. I got a lot of work done (to my standards at least)

During the week I had already cut some bricks in half with a hamer and bolster chisel. That worked pretty well (didn't ruin a single brick). I does take time though, but a lot less messy than doing them all with the angle grinder (my only alternative). The rougher edge will be at the outside and soon covered anyway.

Next I made a mould for the entry, and cut and placed the first 3 rows of the entry arch (on the picture still dry-stacked). My simple indispensable tool worked great for tracing the cut lines. (Question: We are so careful not to align joins, yet the connection between arch and dome is nothing but aligned joints. Is it common for cracks to appear there?)

Then I started laying the dome courses. This commercial refractory mortar mix is weird stuff and takes some time getting used to: It gets sandy fast and the bricks suck water like sponges: I had to be generous with water in multiple ways: Soaking new bricks, spraying the fixed bricks and regularly adding more water to my bucket of mortar. It makes it extra challenging to keep the joins minimal (as I learned in the 2nd course, which turned out a bit wiggly). I'm not at the 3rd course and feel like I'm finally getting the hand of it. My simple indispensable tool does the job. I first position the brick by sight, then gently tap the tool in place for making corrections. Lastly I tap a small shim at the back and I can immediately move to the next bricks.

I completed 3 rows and started cutting the stones for the arch. Tapering with an angle grinder is not easy but not impossible. 12 more arch stones to go (that's 42 cuts if I don't mess any up).

I'm very pleased with the progress. Next weekend is extra long... who knows I can finish the dome !?!

[UtahBeehiver]

I admire your ability to cut your bricks with a bolster and hammer. It shows builders that an oven can be still done the Old School way. If you are tapering your arch bricks, then a small bevel on the dome bricks will be cake and minimize the inverted V we talked about before the hack.

[Kvanbael]

The long weekend is over. I had the opportunity to work almost 4 days in row, and did I finish the dome? Well almost :-). you can see the progress in the pictures.

First day I cut all the arch stones (with the angle grinder) and laid the 4th course. I waited for the next day for mortaring the arch as to make sure the corner stones were fully set. On friday morning I laid the arch, continued on the courses, and by late afternoon removed the arch mould to clean up the spilling (not too soon, as the mortar was near-rock-hard).

Cutting/beveling the bricks with the angle grinder was a lot tougher than I wished. I learned the costly way that a diamond blade for concrete can quickly go blunt on firebricks (I went through one used and one new blade in 3 days). This could be my poor technique (using too much the side force) or just not built for this texture. Also the cuts were rough. The last day, I switched to a diamond disk for ceramics. So far so good. And much cleaner cuts.

Beveling/tapering by sight is always a bit hit & miss. Eventually I created a spreadsheet to calculate the correct tapers or bevels per row (can you guess from the inside picture which rows were "computer aided" ?)

I'm at 11 courses now. Probably 2 more rows and a keystone to go. We'll see.

[Kvanbael]

I admire your ability to cut your bricks with a bolster and hammer. It shows builders that an oven can be still done the Old School way. If you are tapering your arch bricks, then a small bevel on the dome bricks will be cake and minimize the inverted V we talked about before the hack.

Thanks. Just to be clear, the bolster cut was only for plain half bricks, with the 'broken' edge placed on the outside. There's plenty of instructions on YouTube, and it works really well on firebricks. I takes patience though.

[Kvanbael]

This weekend I completed the dome with a 12th row of 18 tapered "soldiers" and a keystone. (will share pictures later). To be consistent with the heat bank under the floor, I also covered the dome with .5" of refractory mortar. (this oven will be primarily for bread baking). I kept the mortar moist all day. So I hope it will also give a little bit of extra strength.

Now I can start worrying about my vent, but I'll start a separate thread for that in the "design styles, chimneys and finish" section.

[Kvanbael]

Latest update: We added 2 layers of 1-inch ceramic fiber blanket and some chicken-wire to hold it in place. (I plan to add another 3 inches of vermiculite on top). This was an easy job with two (I was fortunate my son in law were here to help).

Even though insulation isn't complete yet, and the oven is still missing its flue, I carefully started a first curing fire and ran it for a couple of hours. My IR thermometer came in really handy (just aim the laser to see the temperature). The dome eventually peaked at 120C (250F) right above the flames (which I moved around). When I removed the fire, it quickly stabilised to around 80C (180F) across the top half of the dome. That's enough for the first day. Curious to feel the residual warmth tomorrow...

As you can see in the pictures, the oven is still missing vent & flue. I landed on a design, and I am waiting for some stainless steel parts to be made. Hope to show you that progress soon.

[UtahBeehiver]

Neat and tidy. To help place the pcrete on my done and made an adhoc curved trowel and held the pcrete in place until it self supported then moved on.

[Kvanbael]

Cool idea, and with a spherical dome it works vertically too :-)

[GreenViews]

Kvanbael, Looks like you added some vcrete/pcrete on top of your CaSi board. Did you put something between these layers like aluminum foil? Thanks. NIce fast work! Looking good.

[Kvanbael]

Hey Greenviews. It’s regular concrete. And indeed I put Al foil in between. Otherwise the calsil would have sucked all the water out.

[Kvanbael]

It has been a while. Mainly because I had to wait for my tabletop and custom stainless steel vent... I will soon have more to show on that. Vermicrete has to wait for that.

in in the meantime I started curing fires, as I might as well prepare for cooking without the vermicrete. From the first (very small!) fire, a crack appeared along the vertical seam between two arch bricks. And with every fire it has been growing bigger. Now after 5th day of curing (max temp 400F) the crack has already grown to 4mm! Also the floor bricks are opening up. Basically my oven entrance is getting wider with every thermal cycle so obviously I am worried. The crack runs down into my under-floor heat bank and up into the dome, but there is seems to fade out fairly quickly (at least from the inside). It is not like the entire oven is breaking in two, still a sore sight.

Any advise on dealing with such wide cracks? Should I seal them, eg to prevent smoke from escaping. Do I just have to keep making modest heat cycles and wait until it stabilizes?

Is there a link with curing without the vermicrete? (It does have 2inches of blanket)

[Kvanbael]

Building this oven has been an emotional roller coaster at times. Last week, after a fairly innocent curing fire, I discovered a pretty nasty crack down the front arch. After two more fires, it had opened up to 4 mm. I know... "embrace your cracks and enjoy the pizza"... But, as it is really very visible it took me a couple of days to come to terms with it. (I still need to figure out if/how to seal it).

On the other side of the emotional spectrum: Last Friday my custom-built flue arrived, and I'm really pleased. I designed it to be shallow and thermally isolated from the dome. Apart from the floor, there is no contact with the dome. The intentional gap with the brick arch is sealed with ceramic rope. The entry is double-walled, so that hopefully the outside won't get too hot. I will stuff the space in between with all my blanket left-overs. It is executed in 4mm blasted stainless steel, which gives it a very mat look. It is bolted to the heart and won't budge (now I suddenly start to worry about thermal expansion...)

Now that we finally have a functional chimney, we did an 11 hour curing fire. First 3 hours at 400F, then building up to 500F. Chimney drafted fairly well (39" with ID 8,2"). Some smoke leaking through the front, but in its defence: There was a pretty strong side-wind. We used the heat to slowly cook salmon, potatoes and veggies "en papillote" and a paté.

Still waiting for the granite tabletop, then we can do the vermicrete.

[GreenViews]

I really like your stainless entry! What a great idea. I was wondering about your inner arch crack and if you have seen it continue to get worse? I wonder if it could be from the down and outward pressure from the segmental arch moving the top of the arch column bricks out just a bit. I built the same inner arch style and I am worrying that perhaps mine might crack upon heating also. I am considering adding some v-crete buttressing around the arch area to provide more horizontal support. Is your granite for the whole platform or just in your entrance? That will look nice!

[Kvanbael]

I was wondering about your inner arch crack and if you have seen it continue to get worse? ... Is your granite for the whole platform or just in your entrance? That will look nice!

The crack seems stable. It shrunk a bit to 3mm and staid like that during my last curing day. I’ll anxiously await what higher temps will do to it. I guess the opening is a weak spot in the dome, as it is a hole. A masonry entry would have helped to hold things together.

granite is all around. I told them it was okay to do in pieces, but they insisted on doing one piece ( with cutout). As a result we’ll need 5 strong men to lift it over the dome. That is planned for Wednesday.

[Kvanbael]

Big milestone: We made pizza!

after one more curing fire at 300C (600F) it was time today for the real deal. Got the dome top stable at 850F. Only cleared partially (my wood is not clean). Floor around 700, dropping to 550 near the end.

I am a happy man.

Tomorrow I’ll get clean oak wood. The day after the tabletop arrives. I guess there’ll be more pizza parties this week.
This weekend I’ll start on the vcrete.