Challenges and progress of building pizza oven on a slope

[JRPizza]

Thanks - the screen shot from the Exel file really helped. Your Excel skills are fine but you are mixing units. Either convert your brick dimensions to centimeters or your other dimensions to imperial. See below, the first row is metric (with metric brick dimensions) and the second row is imperial. 17 bricks is too many for a small arch (you will actually get a negative joint thickness) so I did one for your dimensions with 15 bricks. It gives a pretty tight joint (.18 in). If you want to make the joint larger you can cut into the thick part of the bricks a little (the number input into column O). You could also go to 14 bricks - it does not look as good to me without a brick at top dead center but the inner arch is not really seen and you could do an uneven amount on the outer arch. I would also consider asking DavidS what dimensions he recommends for door opening as I believe he is not only an expert on cast ovens but also on smaller(ish) oven sizing.

	Opening	Opening	Ratio	Ratio	Inner	Brick	Radius	Circumference	Circumference
Height	Width	Height	Height	Width	Radius	height	outer	Inner	outer	# of bricks	t joint	Brick W1	Brick W2
40	42.5	26	65.00%		21.25	11.43	32.68	66.76	102.67	15	0.46	6.35	3.96
15.74803	16.73228	10.23622	65.00%		8.3661	4.5	12.87	26.28	40.42	15	0.18	2.50	1.56

[Yokosuka dweller]

Thank you JR. I will try to recreate this in the excel and have another go at cutting mock ups for the arch according to these numbers. Perhaps my arch form is off, I will check that too.

[JRPizza]

When I cut my arch bricks, I "indexed" the bricks on my jig by placing the 2.5 inch sides down. You can see in my picture where I'm cutting down from the top leaving most if not all of the 2.5 width for the top of the arch. After cutting all the bricks I flipped them over and aligned the cuts (mostly by eye) to complete them (my saw would not make the complete cut in one pass). I quickly found out that the sides of some of the bricks were not at 90 degrees to each other so that the opposite sides were not parallel, which resulted in slightly different angles on each side. I sorted the bricks with a square to get the best ones and the angles were closer. It is not something I even notice now when I look at the oven but thought I'd mention it. I just used the bricks that I "rejected" for the dome where it didn't matter.

[Yokosuka dweller]

Thanks for this JR - I might have to do something similar. I don't own a proper wet saw, but a friend of mine has a normal 'hack saw' on a stand, which I have to use with diamond blades-cutting the bricks dry. It doesn't have rails that allow me to pull or push the blade but just up/down motion, so that probably means I'll have to cut the arch bricks from several sides to get the cut. I haven't gotten the saw yet, so will see how this can work.

edit: figured it out.

[Yokosuka dweller]

Nice weather here today, some winds and cool. I had a few hours after taking my daughter out shopping, so bought some new and shiny bricks and placed them.
It was a bit tricky since I have a hole in the hearth for a potential gas (or smoke box) connection, so had to start the floor at that point. I made a pipe shaped piece for that hole and probably need to fill the remaining gap with perlite and/or sand before moving further. Bricks are overall pretty level, but there are a few high/low spots on the insulating layer, which I need to adjust with angle grinder and some silica sand next, or leave them as is, not sure yet.

In cutting the circle of bricks, I used an angle grinder and that was surprisingly easy. What helped me here was to have the outside cut of the circle form remaining as a piece of wood, so I could use that to trace the shape on the bricks before cutting.

I stopped short of the oven entrance/door. That part is still complicated and I'm not sure how to cut the bricks, especially how thick/deep I have to cut the entrance bricks. I'm scouring the forum to better understand this part.

Funny thing is I realise the old firebrick I had inherited are larger and thicker than the smooth new ones I bought, so that will create another variable when building the dome.

More to come.

[UtahBeehiver]

Are your doing a tapered inner arch? It is a little more difficult if you do not have a wet saw but still doable. If you go this direction, the placement of the arch form is critical as well a properly design "adjustable" IT. I have attached a couple pics to help you visualize. This is one of the most difficult concept to understand but it is worth the effort. A note, you must start with full length bricks to do taper arches and you begin with the top center brick on the arch and work you way down. The attached pic is for a partial arch with vertical side walls but the concept and process is the same for full arches as well.

[Yokosuka dweller]

Thanks for the guidance Russell. Indeed I was planning to do the tapered arch, and kinda can visualise the reasons for the cuts so the arch bricks become part of the dome. I tried cutting tapered bricks the day before and bodged the first brick, the second attempt was better. So I think its possible to cut, even with an angle grinder, just need to cut 'outside' the scribed line and allow for sanding down with patience to get the right dimension. It's a dusty affair for sure.

Then, I guess to figure out the correct placement of the arch is done with the IT? Basically placing the TDC arch brick on the form and adjusting it till enough of the overhang of the brick is 'inside' to allow an angled cut as 'floor' for a half brick on top? So 4,5" overhang at an angle guided by the top of the L-bracket on the end of the IT? Makes sense, or am I off in assuming this is the way to figure out arch placement?

I had a very basic IT done only in wood, so non-adjustable. I'd really like to make something adjustable, but don't have a welder nor any welding experience, is there a way to make adjustable IT without needing to weld? I have't really understood yet why the IT has to be adjustable - haven't found the answer on the forum yet. At what point do I need guidance for a different radius than that of the oven dome?

Edit: Found great example of non-weld adjustable IT: https://community.fornobravo.com/for...n-dallas/page2

[Yokosuka dweller]

It's been raining and I have had to work, so haven't had a chance to progress much. But there have been small things I could do when taking break from work.

I copied Dwatkins non-weld IT (thanks!) and after some cutting and grinding it seems to work. Used a caster wheel bearing as pivot; drilled holes in the center to get the IT to take off from the real center of the oven and not 1" outside it. I use a wooden brick - as inspired by JRPizza to place the IT in center of oven. Still it causes the pivot point to be half inch above the true center. I believe that won't make a big difference even when placing the arch, but I could be wrong. My oven will be small (31,5" ID), so half an inch of extra height would probably not be a problem.

Now I have a potential problem. I made the entire landing, including outer arch sit on perlcrete. But I didn't think about the fact that the outer arch which will have the chimney will be pretty heavy. So now, before I go any further I wonder if it would be alright to ask the experienced community, including UtahBeehiver and DavidS whether you think this is going to be an issue for the stability of the outer arch? While a hassle at this point it still is possible to adjust before its too late. I could drill a hole in the perlcrete to accommodate a jigsaw blade and then saw out the perlcrete+replace with normal concrete to make sure the entire outer arch brick sits on concrete. Is that better or will I be fine on the perlcrete?

Simon

[Yokosuka dweller]

Have laid the first two courses now using half bricks and using the premixed Japanese castor refractory cement. Quite an interesting experience to use this stuff, it has lots of different coloured aggregate and sets within 30mins. Moreover, I get only 1 chance at placing the brick correct. If I remove the brick or realign the 'set' is gone.

I have finally found lime, which is called Secil Natural Hydraulic Lime (NHL) 3,5 - imported from Portugal. So once I run out of the expensive refractory cement mix, I will switch to homebrew.

I am not using tapered bricks but I would like to keep relatively small internal joints between bricks. I wonder at what point do I need to start beveling bricks to avoid 'inverted V'. Am I good to go with regular half bricks for another couple of courses?

Merry Christmas!

[Yokosuka dweller]

A few updates - made 3rd course today. Am interlocking the arch bricks with the main dome, not sure if that's good or bad but it seemed a good idea at the time. From 4th course I won't do that but will hopefully be able to place a 'normal' half brick on top of the arch brick, if the angle is acceptable.

I also drilled out the perlcrete down to the concrete slab and refilled with normal concrete for the areas where the outer arch with chimney will sit. I hadn't thought about it before, but that part will be heavy and I don't want it to sag later on. I haven't decided yet what I will do with the floor there. I looked at some nice granite slabs - used precision granite is available, but the slabs are 10cm thick, so bit overkill. Maybe a white or black cement floor would do. Not sure.

Have started to grind down 0.9 or so cm on the upper sides of some of the dome bricks to minimize the 'inverted v'. Seems to work, although I wasn't super precise about it. It's a bit of a rough build, but I hope it will work.

Just about ran out of the Japanese refractory cement mix. It's been great to work with, sets fast, so small batches. But I will switch to homebrew for the rest to save some money.

[Yokosuka dweller]

Mortared almost all arch bricks now. Had some trouble with the homebrew not sticking/locking. But turns out I needed to wet the bricks more, that done, it seemed to work. Also, I've been trying to anticipate the 'dreaded droop' to the front, I think I manage to adjust fairly well but one side seems to be drooping a bit. I hope I can manage to adjust next course.

Arch bricks are not cut totally in line on the inside, but I think mortaring them in first and then grinding down wrong angles would work. I find it difficult to precisely gauge exactly when 5th or6th course (?) to go above the arch. I guess that will sort itself out as I get there. But looks like the arch on the outside is fairly balanced/symmetric. Even I had to use angle grinder to cut the arch bricks. Definitely a dusty affair. But @JRPizza's arch spreadsheet really super helpful. Thank you for sharing this with novice builders like myself.

Am thinking about a fat slab of granite for flue area/landing. I will put in a 1,5" steel pipe for heat break so hopefully granite on the outside of that would be able to accommodate the heat without breaking or spalling.

[UtahBeehiver]

The flue area is too hot for Granite. The radiant heat will cause the Granite to break. It would be okay for the landing though.

[Yokosuka dweller]

The flue area is too hot for Granite. The radiant heat will cause the Granite to break. It would be okay for the landing though.

Okay, that's a shame. Granite would look very nice in that area which anyway gets sooted and dirty from cooking action. I will talk to local stone mason to see what they recommend, and otherwise go with firebricks till landing area.

Arch now set! Feels good to have that step done. But I also know next step to fit dome bricks into my poorly cut arch transitions will be a tricky affair and I will need to find the right time, a day when wife and kids are out the house and I don't have any work to do, then I can focus on 6th and 7h courses, which likely will be the ones where the arch/dome transition will take place. I see some builders have their arch/dome transition in the 6th course (above ground), such as Utah, but others in 7th course, I guess it doesn't matter does it?

[Yokosuka dweller]

After being away for work for a week and then back to rainy days, I finally found time to close the arch. I had a bit of a 'dreaded droop' case to accommodate. I used a stick affixed to the indispensable tool to keep the course at the correct height all the way round. In front of the arch I had as much as half inch droop to sort out. For sure mortar was my friend as were strange cuts to accommodate as much brick as possible and get back to desired height and circular shape. It worked, but for sure I won't win a beauty contest. Now I'm just hoping that it will be strong enough to take firing.


If I were to do this again, I would much earlier have started to use a height gauge to ensure I won't gradually drop height as I get close to the arch. I was warned by the old-timers on here and thought I'd be able to prevent it. Lo and behold, it happened. Good experience!

I assume things will get a bit easier the next couple of rows. But now I guess I have to start using 1/3rd brick cuts to minimize horizontal mortar gaps between the bricks? Well, I got my saw and will cross that bridge also.

[Yokosuka dweller]

Finished 7th course, mostly half bricks but having to cut off wedges of the vertical edges more now to keep the 'inverted v' to a minimum. Pretty easy this course and I am roughly back to round shape, but I expect next course which will be almost vertical to be difficult, as the bricks will want to slide off position.

Also, can see that horizontal mortar gap between the courses will increase, maybe now is the time to start beveling the bottom of the bricks to minimize that gap?

Anyway, I ran out of cement and am almost out of bricks, so need to do a run to the hardware store first before anything else.