36" Pompeii in Indiana, US

[GreenViews]

IT advice welcome: my Arch radius is below my floor and I've seen people do both of the following. Anyone have negative or positive experience to guide me in deciding to either:

a) Keep center bricks out of floor during build and make a single length IT or
b) make a complex IT that I change with each course?

[Mongo]

Oven placement: Which is better? very close to edge of table or a few more inches back. With a few more inches back, I can still reach my hand just past the door without bending over. My oven base is higher than normal perhaps. It will be almost 8" higher than table so sternum level to me. Low dome 15" with 9.75" high door.

I strongly recommend the forward placement. You will want not only want to reach your door, but reach into the oven. My front arch is 8 inches from the front edge of my stand. I love the position. I can reach in and dump a load of charcoal from my 'mini chimney starter' into the center of the oven, then hand place kindling without bending at all.
Here's the front of my 42 inch oven with a 72" peel reaching all the way to the back of the oven. Should give you some perspective.

[UtahBeehiver]

Aren't you doing a low dome? Then you will need and adjustable IT since the radius at the top is much small than at the floor. The critical items for an IT is that the line from the pivot point (make sure it is not offset from the center of the oven) along the IT rod the the "L" bracket intersects and mid point of the thickness of the brick. Second, the pivot point is at the floor elevation of the fire brick

[GreenViews]

Aren't you doing a low dome? Then you will need and adjustable IT since the radius at the top is much small than at the floor. The critical items for an IT is that the line from the pivot point (make sure it is not offset from the center of the oven) along the IT rod the the "L" bracket intersects and mid point of the thickness of the brick. Second, the pivot point is at the floor elevation of the fire brick

Oh, I was assuming that the brick face should face the arch radius center rather than the center of the oven floor. Would not that be more traditional masonry arch? But no matter tradition if what is right for an oven build is the brick face toward the center of the floor. Having IT originate from center of floor and adjusting length for each course would be pretty simple versus what I thought I needed to do. But look at my drawing comparing the two and it becomes apparent that the brick face and therefore cuts between the bricks becomes most pronounced and significant midway up the arch. Is this a problems? It would change the physics between courses in the case of mortar failure, but I'm not sure if it is a good thing or a bad thing.

[UtahBeehiver]

I did not do a low dome so my IT concepts are based more on a full hemi sphere. I did not see how you could have the true arch radius point down in the insulation structure. Ideally the face of the brick should be perpendicular to the arch radius point as noted in your diagram 1, The second reason of the IT is ensure consistent brick tilt and diameter of the oven. If you can practically make the pivot point down in the insulation layer, have at it.

[GreenViews]

Thanks Utah for your awesome help and prompt reply! I'm just trying to grasp this stuff correctly so I don't make stupid errors I regret or worse yet that cause significant problems with my build.

[GreenViews]

I strongly recommend the forward placement. You will want not only want to reach your door, but reach into the oven. My front arch is 8 inches from the front edge of my stand. I love the position. I can reach in and dump a load of charcoal from my 'mini chimney starter' into the center of the oven, then hand place kindling without bending at all.
Here's the front of my 42 inch oven with a 72" peel reaching all the way to the back of the oven. Should give you some perspective.

Thanks Mongo! Sounds like perfect advice to me. I did some more recalculating this morning regarding my build and placement based on your advice!

[GreenViews]

Some work done on oven today. Slower than I hoped. Weep holes, metal screen, CaSi board, started on subfloor thermal layer, then created a temp shelter for the project.

[GreenViews]

Some questions at this point:
a) my CaSi board cut out was messy and imperfect. Should I worry about the 1/16" gaps at places between the board? Also, at least one place is slightly higher because of a width variance in the board, which also arrived with some cracks in it, but I'm not thinking of worrying about those.
b) Turns out the used firebrick I saved for the oven floor only covers 2/3 of it. I hadn't calculated. These are possibly a medium duty firebrick where the new ones I can get locally are a light duty. They are also slightly (about 3/32") different width. Should I worry about the different heat retention properties if I mix the different types in the subfloor layer? (I plan for a layer of splits for cooking surface on top of this layer). Also, what should I do about the thickness difference? fireclay/sand layer to even out is what I remember seeing in forum. 50/50?
c) I could put the old brick in the center and the new brick around the edges in case there is a heat transfer variance noticeable from this thermal layer. Sound good?
d) I also have some old clay bricks, both red and yellow, some of the red ones are better quality for high temp it seems (high pitched clink when knocked together). Should I try and use these? The problem is all the dimentons are a bit smaller than the old fire brick even though the height matches that of the new firebrick, but I could save money putting them under my dome base? I'm going to avoid using them unless someone suggests I should because I can afford to buy new firebrick. I still hope to use the old firebrick in the floor.
I'll do my best tomorrow if I don't get feedback, but very happy for any advice. Wish me luck

[GreenViews]

Just found answer to how to level the bricks from UtahBeaver posted to another build:

"06-05-2020, 11:31 AM
1. FYI, you do no mortar the floor bricks down, they need to free float for expansion and contraction. Same with joint between floor and first half soldier. You can do a 50/50 sand clay slurry if you need to level bricks but not a setting mortar. 2" 5 to 1 por v crete equal to about 1" CaSi

2. Up to you on the bevel,use you IT to see what the angle is and decide it you want to bevel the top of the soldier, my guess the angle on a 1/2 soldier will be slight Half soldier is better than a full soldier, less outward pressure from the dome."

Still considering what to do about the sub-floor bricks. With the height difference I'm not sure I want to add 3/16" of sand/clay mix extra between the layers and if the point is for the bricks to float, then they may eventually settle a bit if my height differences are too great, or so I reason. Also, possible heat transfer difference with older bricks and different type of brick. Even though I have a split layer to add above this, I fear it may still affect hot or cold spots. If I don't hear back from someone before I start on this, I'll just save the old firebricks to use near the top of the dome. A higher heat transfer brick there may give me good results anyway and most have clean enough edges for inside face. So I probably just talked myself into doing that. maybe I'll shave down the main high spot on the CaSi board. I considered adding a fairly thin layer of 5:1 perlite to even out and make up for poor seams in CaSi, but not sure I need to and then I'd have to wait a day. I do have lots of bricks to cut and saw to set up. Will consider as I start work in earnest today. I plan to mix up some 5:1 for around the CaSi to keep it contained and from cracking anyway. Will get a feel for how easy it is to work with at that time.

[GreenViews]

I've seen people cover their CaSi board with aluminum foil to keep moisture off from the next layers. I have some FSK paper left over from a project https://jrproductsinc.com/product/fsk-paper/ but I decided to just use aluminum foil here since I don't know what chemicals might have been used for the fire retardant properties and this layer might get pretty hot. I think I'll cover the outside of my dome insulation with it where the temps will be cooler as a outside in vapor barrier there to keep any leaks from getting into the insulation, but with a slit at the top I suppose to allow any steam to escape the oven.

[UtahBeehiver]

Wrapping the CaSi board with aluminum foil to keep water out can also keep water in, water has what I call "sneak-o-sity" so by layering the board will also keep the water that finds it's way in trapped. You need to consider a vent at the apex of the dome so when water converts to steam, it has an egress point rather than building interior dome pressure. I just recently posted what Gulf and I used for venting the dome (actually Gulf's innovation)

[GreenViews]

Thanks, I actually saw your comment this morning about dome venting and added something similar to my Amazon list for purchase when I get closer to insulating dome. Appreciate the feedback. I was considering just something on top of the board to keep the wet mix to be dried out too fast via the CaSi board. I guess I was also for a minute thinking it might protect the board from moisture from top, but I guess not such a great idea then. Can I put either a thin clay/sand moist mix or a pcrete mix right on top of the CaSi safely without too fast drying out? I'm actually at the moment leaning toward a 1" layer of 4:1 perlite: refractory mortar layer on top of the CaSi board since my board came kinda broken up and I purchased a single bag of Pratiperl, which is a much smaller, more even perlite that I might use there to give me a smooth surface and keep the cheap perlite for butressing half soldier course and encasing the edge of the CaSi to keep it from breaking apart by my feet hitting it, etc.

[UtahBeehiver]

The 50/50 does not have to be a slurry it can be dry mix as well.

[GreenViews]

Had just a couple hours to work on this today and the unevenness, large gaps and flaky nature of the CaSi I purchased was really bugging me so I covered only the top so CaSi wouldn't pull moisture off too quickly (not bottom of CaSi which is left with only metal mosquito screen so It could drain) and added a layer of 4:1 Prateperl to refractory mortar. The Prateperl I purchased on Amazon and is a very uniform, fine perlite which allows a smooth texture and the refractory mortar was purchased at Menards. This is not standard material nor standard practice and possibly the wrong thing to do, but I was concerned about structural integrity so made my best judgement for better or worse. The 4:1 mix will have slightly higher strength than 5:1 but lower insulating value, but that's ok because it is the layer between the brick and the insulating layer so hybrid function not a problem I think. Will foil on the top surface of CaSi trap water/steam in that for some reason doesn't drain out the weep holes below? Time will tell I guess.

Tomorrow I hope to buy more bricks, assemble the tile saw I bought and cut some brick if my free time allows.