42" Pompeii construction in Adelaide

[P3 Stoaker]

G'day All,
Many thanks for taking the time to reply. I 'think' the position I have will be ok but there are a few points you have raised I didn't quite get.
For info I plan to have quite a low entry, 42 and half inch dome ( adjusted metric) with a 270 mm (10 and 5/8 inch) inner arch opening height. That might be why my IT to TDC angle looks a little lower than most.
NCMan, All good, thanks I'll lay tight-ish.
Russell, My IT pivot is very close to correct in last post photo's but I will be modifying the lower mount ( fork bolt) to be even better. You mention 'The dome will be there as long as you follow the IT'. An important aspect, I've been wondering how high or low to position the IT on that TDC brick to mark and cut. I think its more about mark and cut that TDC at a reasonable position and the dome will be there. Would you agree the height of the IT where you mark TDC is mainly about having enough brick cut to meet the dome course above and a little below to cut the lowest inner corner off ? In your reply you say 'The bottom part of the inside of the arch form needs to sit on the ID arc of the dome' . I don't understand why that is and I'm wondering what I'm missing??
JRPizza, The form I made isn't all that wide and therefore cannot be positioned in line with the outer edge of the arch or the bricks will fall off. I planned to measure the outer edge of the bricks to the outer edge of form to keep vertically aligned, do you see problems? I think I get what saying in the next paragraph. Would you agree in my photo 3 the short side of the IT 90 deg piece of angle could be used where it is to mark the inner radius, and looks ok to me ?? A brick nested in the it would have a little steeper angle, but even as it sits it seems reasonable to me ???. I think you were saying the TDC needs to be 'IN' far enough to have a good cut face on top to intersect dome and also enough to cut the little corner off, lowest inner corner?? As far as I can determine my position in photo 3 will achieve this ?? Till now I've been wondering how high/low to position the IT and mark the TDC but I now see it more as you mention, balance the cut as described above. In your sketch 2 it appears as if a line drawn across the front edge of the lowest arch bricks would go very close to the outer radius. In sketch 1 the TDC outer edge appears closer to the inner radius. Am I seeing this correctly?

I'm going out to dry build the arch again. Certainly appreciate the feedback and I owe you guys big time.
Regards
Greg

[UtahBeehiver]

JR is right, I overlooked where the bottom of the arch form sits, The bottom part of the inside of the arch form needs to sit on the ID arc of the dome. You also need to include at least 1/2" of release on the arch form to be able to get the form out after the arch is done. Also save the arch form as a template for you oven door.

[JRPizza]

Here is a few sketches of where the arch bricks should be placed to properly intersect the dome.

[JRPizza]

I have a question about placement of your arch form. I found it much easier to calculate how far forward I wanted my arch and set my arch form with the front edge at that point and made sure it was perpendicular to the base. That allowed me to index all my bricks with the forward edge flush and helped keep the arch aligned. It appears you have your form set back and I was wondering if that was done for a reason?
Also about your placement - in your third pic I can see where the IT bracket sits in relationship to the TDC brick, but you need to check where a brick nested in that bracket will sit on top of the TDC brick. You can see in the attached pic that my arch is placed so the brick in the IT has enough rearward projection (to the left) to have the inner radius cut on the lower half and an angle for the topping dome brick on top. Ignore the line drawn on the upper right it was obviously not used.

[UtahBeehiver]

The dome will be there as long as you follow the IT. I cannot see how the IT will be set on the other end, The pivot point should be a floor elevation. The first brick at the base needs to be cut to follow the ID of the dome but the placement fore and aft is correct once you cut the arch shape. The top dead center of the tapered arch is where you start the work you way right and left of TDC. Note the cuts will be skewed and each one different so do NOT cut them all the same. Lay the the TDC brick with the IT. Then looking towards the inside of the dome, the next brick left of TDC, the right side of this brick will have the same angles and slopes of the left side of the TDC brick, then mark the left side of the new left brick of TDC with the IT and connect the dots, then repeat the process with the second brick left of TDC and so on and so on. Repeat the opposite process with the bricks right of TDC. The light bulb will click on.

As mention by NC the only gap on the floor is the a cardboard thickness between dome wall and floor if the floor is "cut to fit inside" dome, this gap is not filled in with any mortar, ash will eventually fill in.

[NCMan]

G'day All,
Russell and NCMan, Thanks will do. I probably should have added why I asked, which was a post somewhere saying to leave a small gap for expansion movement. Anyway I'll lay tight. Thanks
One other last check for anyone's opinion before I'm fully committed. And yes it's about the tapered arch, sorry but just wish to confirm, not sure if I'm stupid or cautious, hopefully the latter !!!
Photo 1 and 2 show where I plan to have the lowest inner arch bricks in relation to the extended dome arcs. Photo 3 it with the IT tool set at length and looks ok on the TDC I believe ?? My question is how do I know what the height of the dome will be there at the top where it intersects the arch ?? Photo 4 shows the IT a little lower which doesn't look right. How do I know the dome won't intersect at that height which seems too low?
I have attempted to measure/predict height but I've not found reference to doing that here on the forum and guess most don't do that ??
A huge thanks for all the advice so far. I live in the famous Barossa wine region north of Adelaide in South Australia. Come and visit and I'll show you around !
Regards

I think where the confusion may be is that a small gap around the edges for expansion is recommended, if placing the floor inside the brick walls. However, for the floor itself, yes, lay them tight. Sorry for the possible confusion on that.

[P3 Stoaker]

G'day All,
Russell and NCMan, Thanks will do. I probably should have added why I asked, which was a post somewhere saying to leave a small gap for expansion movement. Anyway I'll lay tight. Thanks
One other last check for anyone's opinion before I'm fully committed. And yes it's about the tapered arch, sorry but just wish to confirm, not sure if I'm stupid or cautious, hopefully the latter !!!
Photo 1 and 2 show where I plan to have the lowest inner arch bricks in relation to the extended dome arcs. Photo 3 it with the IT tool set at length and looks ok on the TDC I believe ?? My question is how do I know what the height of the dome will be there at the top where it intersects the arch ?? Photo 4 shows the IT a little lower which doesn't look right. How do I know the dome won't intersect at that height which seems too low?
I have attempted to measure/predict height but I've not found reference to doing that here on the forum and guess most don't do that ??
A huge thanks for all the advice so far. I live in the famous Barossa wine region north of Adelaide in South Australia. Come and visit and I'll show you around !
Regards

[UtahBeehiver]

Agree, after the floor is laid you can knock off any high spots with an angle grinder and a diamond cupped wheel.

[NCMan]

Meant to ask. What does everyone think about how tight to lay floor bricks? I’m using a 12” square 2 “ thick fire brick/ paver layed on Cadillac board with dome on top of floor??

Tight as possible, preferably at a diagonal to the front entrance. No mortar under or between them. It's important to get them as flat as possible. Your peels will thank you later.

[P3 Stoaker]

Meant to ask. What does everyone think about how tight to lay floor bricks? I’m using a 12” square 2 “ thick fire brick/ paver layed on Cadillac board with dome on top of floor??

[P3 Stoaker]

G'day All,
Thanks Tom. Yes my casil board is quite good, still had some thickness deviation but mainly on edges and I cut most of it out. I've cut all 3 layers the same and had planned to flip the middle layer over to better insulate the floor against heat loss but Russell brought up a great point, that's more likely to capture moisture. I'm now wondering if I should position all the joints in line so any moisture goes through and drains away, as planned through the gaps in the tiles??
Thanks Russell, I think I'll have the break to perlite at the outer edge of the inner arch. This does mean a break in all above the tiles under the Casil.
Regards
Greg

[UtahBeehiver]

You can use the sand/clay mix between the CaSi and the fire brick floor as well if you find you are too out of level. But an 1/8" is not going to be a deal killer. As far as insulation under the vent chamber, up to you. I did it because I had the material and put in a floor 316 SS thermal break. There is a cast build going on right not where the builder remove a wedge piece under that vent and dome transition leaving a small contact point the surface then filling the wedge with Vcrete. I did something similar on the vent arch to inner arch transistion. Transition to granite and brick, you just have to work out what is best for you.

[GreenViews]

Greg, Regarding CaSi under entrance floor, someone (I was thinking it was Utah, but can't find post now, so not sure) recently repaired their near decade old build by removing the insulating board under entrance (degradation from moisture) and replacing it with pcrete as well as drill weep holes. If it was a place of failure, so for me, I'm planning on pcrete under my entrance floor. That will allow me to use different width materials outside my door/ inner arch anyway. I found buried on my project a piece of granite I think I will incorporate somewhere in my entrance, but I haven't looked at expansion and heat characteristics yet so do't know if I'll use close to door or further out cooler placement.
Tom

edit: p.s. your CaSi board looks so much more uniform and in better shape than my 3" board came to me!

[P3 Stoaker]

G'day All,
I have 2 questions but they are tricky to explain, apologies for the long post, I'll try to keep it as short as possible, and many thanks if you read on !!!
1 As seen in photo no 1 I have large area's each side of the dome. The dome will sit on 3 layers of Calsil board, (3 inch) which will be on mosaic tiles for drainage(photo 2) Surrounding the Calsil I need something to fill the area to support slabs of granite ( 1 and 1/4 inch thick) , thinking of perlite (5;1) simply because its light and easy The question is where to change from the casil to the perlite??
I will have a tapered inner arch, and vent arch touching but not tied together. Given the Calsil probably isn't needed under the vent arch, I could stop it in line with the outside of the inner arch, and possibly also have a break line in the floor bricks, meaning a total break in everything above the hearth, in line with the outside of the inner arch.
Alternatively I could take the Calsil all the way to the very front arch, or 3rd option possibly make the transition to the perlite at the outside of the inner arch but split the floor bricks over the Calsil/perlite join. I'm using floor fire bricks 305x305x50mm (12 1/64 inch square by 2 inch), so a lot bigger than a normal size brick. I'm just a little concerned as to where to chance from the Calsil to perlite???

2 I'm also considering what to do about the height difference between the oven floor bricks, 50 mm (2 ") and the granite slab I will have surrounding the oven, 30mm (1 3/16 inch) as they both sit on a level surface, casil under oven, perlite under the rest. Even if I have a strip of the granite along the front edge outside the arch, it will only be around 100mm wide(4"). So I could just bring the oven floor bricks all the way forward to the front edge and have the 20mm (25/32) step downs on either side. Or, I was considering a shallow grind down of the floor bricks within the arch, cut exactly that wide, so over the length of the vent arch dropping from the 50mm to 30 mm to be the same height as the strip of granite along the front edge ?? I'm starting to think the shallow grind down could be tricky, and the little steps to the side might be ok, what do you think??
Really appreciate any feedback.
Kind Regards

[P3 Stoaker]

G'day Russell,
Thanks for the info. I've gone with more floor insulation than initially thought I would 3 " casil board, given so many posts say they would have fitted more. So I plan to have quite a bit of dome insulation as well, leaves us able to do more with the oven and your three day cook sounds awesome !!!
Just reading Greenviews post where you say about "NOT" aligning the layers of casil. I have three by 1 " layers and was going to mis-align but I see what you say in that may trap moisture. I will align joints now.
Just one question, whats the most hearth/structural slab deviation from flat that you think is acceptable? As mentioned I'll have tiles, 3 layers casil, total 3" and the floor bricks directly on the casil. I don't see how levelling sand under the casil would work given I'll have tiles and drain holes?
I also have 2 tricky questions which I cant really draw. I'll post soon and hope they make sense and a few reply !!
Many thanks again for the help.
Regards
Greg