36" Pompeii Build Redux - This Time In CA

[totalnewbie]

Great work! Very helpful for a beginner.

Which HF saw did you get? I think they have two.
What is the state of the art for whether you build the dome on top of the floor or cut the floor and put it on top of the calsil boards? Are there trade-offs?
I think 2" of calsil is standard. Are people using 4-6" seeing better oven performance? Is it worth the extra cost?

Thanks for sharing!

[rsandler]

Great work! Very helpful for a beginner.

Which HF saw did you get? I think they have two.
What is the state of the art for whether you build the dome on top of the floor or cut the floor and put it on top of the calsil boards? Are there trade-offs?
I think 2" of calsil is standard. Are people using 4-6" seeing better oven performance? Is it worth the extra cost?

Thanks for sharing!

I think they have a 7" saw and a 10" saw--you definitely want the 10". For some of the weirder cuts like tapering arch bricks, even the 10" isn't always big enough.

Best I can tell on the floor vs. around the floor is a matter of taste. Technically you are more able to replace a damaged floor brick if you have the dome around the floor, but that happens super rarely, so doesn't seem very relevant. I cut the floor on this oven and on my old one in DC.

4" of insulation is pretty common if you look around the forum, although FB only recommends 2" of ceramic fiber board, so maybe that's overkill. I only ever had the one oven, with 4" of floor insulation, but I pretty much always would have been happier with more heat retention. That said, I only went for 6" on this build because I wanted a little more height, and the marginal cost of more boards was 0 (had to order a second box of 9 boards to get enough for 4").

[totalnewbie]

OK. $499 for the big HF tile saw. Check!

Thanks for info on floor insulation. I'll do 4". Two layers of cal-sil board. And some shopping.

I'm sketching the layout and I'm not clear on how the arch for the oven opening works. I see that it is back cut at an angle to meet the dome courses. But how long is that brick, and how much does it stick out in front of the dome? If it's a full 9" brick it seems like it sticks out pretty far, and then I build the vent with 9" bricks -- so the whole vent area is pretty deep. Or do you cut the length of the bricks for the opening arch before the back cut? Are they only 4.5"?

It's early days, but I'm calculating how deep the hearth is going to be -- and I'm not clear on how deep the oven really is, yet.

Thanks to everyone for the feedback!

[rsandler]

You want the inside corner of the base of your arch to intersect the curve of the dome, and then probably want that first brick to taper away from the opening, along the curve of the floor. Combined with cutting at an angle to meet the dome, you end up with a rough pentagon shape. Further, as you go higher up the arch, the bricks need to extend a bit farther inside to catch up with the dome surface (which is curving away toward the center as you go up. These posts (from others) on my old build give the idea; UtahBeehiver has shared variations on the first one all over the forum.
https://community.fornobravo.com/for...053#post197053

https://community.fornobravo.com/for...302#post198302

To make the length work, you either need to start with full bricks, or be clever and cut full bricks on the diagonal, but you're not extending the entry much beyond the circle of the floor. You can use your IT to mark the length and angle for where the arch will meet the dome, though I tried that on this build and it was kinda a mess .

For more specifics, on both my previous build and this one, the inside face of the arch was 3.5", and the goal was to have the surface that meets the dome 4.5" long.

Hopefully that's clear-ish; all of this is easier to work out with pictures, and I don't have access to any of that right now.

[BTW You may want to start your own build thread to ask some of these questions--you're more than welcome to ask them here, and I'm happy to answer as best I can but you might get more/better responses from the seasoned builders of the forum in a separate thread ]

[rsandler]

Ended up cutting and mortaring in a couple bricks for the first course on Wednesday, but then had Thursday evening to really push and got the whole first course cut and set. Also pulled the arch form and cleaned things up a bit.

Cut maybe half the bricks for course two this afternoon and put the first few on, but otherwise not a ton of progress from today. Realized that between one thing and another I've mostly used up my first 100 bricks (or will have by the time I get done with course 2). So, guess I'll need to make an early morning trip to the brick yard tomorrow to avoid losing the weekend. Fortunately they're open Saturday mornings!

So far the brick cutting jig with tilting the saw blade is working great--nice to get two bricks per three cuts. Getting the saw angle adjusted is more guess-and-check than I'd hoped. I have one of these nifty magnetic angle finders, where you zero it out on the table and then stick it to the blade to get the blade angle. But it doesn't seem to be reliable enough that I can take the angle from Dennis' calculator, shift the blade to match, and get perfect bricks every time. So it goes. Having the jig and the fixed blade angle at least beats eyeballing and using brick shims to get the angle right!

[rsandler]

Finished up course 2 this morning. Got the angle on the blade dialed in a little better, so had less adjusting angles or flipping bricks upside down. The inconsistent thickness of the bricks is causing some weirdness too, but I think it's looking pretty good on the inside so far. Hope to start course three today.

[rsandler]

Finished course 3 this afternoon. Some fiddling required due to my brick-cutting jig starting to warp, in spite of my efforts to waterproof it. After finishing the course, I took it back to the garage and ran the bottom through the drum sander to flatten it, and hit the back edge that sits against the brick saw fence with a hand plane to straighten it, but not much could be done with the top surface that holds the brick. Debating whether to tough it out or shell out for some sheets of plexiglass or similar impermeable substance to make a new one. Probably will go for toughing it out, and remake another plywood model once I switch to 1/3 bricks, since the side angle will change at that point too...

Having a heck of a time avoiding mortar stains too. Had a little bit of luck cleaning them off with undiluted vinegar. In one of the pictures you can see a cleaner area on the top of the entry arch, where I was trying to scrub what will ultimately be the reveal. Hoping that vinegar does the trick longer term--I know muriatic acid is the go-to for removing mortar, but that stuff sounds nasty, particularly in the relatively enclosed space of an oven.

[rsandler]

Higher still. Finished most of the fourth course yesterday; today's work was putting in the last couple bricks; the closer in particular was a pain. Mortared in one brick for course 5 to have something for the rest to hold onto, and to give a reference point for the level--it looks like course 5 is going to be the one that gets over the arch, and that's going to be hard enough without a reference for how thick the bricks need to be.

Did another round with the vinegar, this time with a wire brush to boot and so far it looks like the mortar stains are abating.

Question as I think ahead to the enclosure: how do folks usually pull off the transition from walls to roof using steel studs? I've never worked with metal studs before. I get the concept of laying track, then fitting studs into the track, then another round of tracks on top to make the box. Can't quite visualize how to then connect a roof, and haven't been able to puzzle it out from others' pictures around the forum.

[Macrinehart]

Just curious about the cleaning of mortar stains. I've been removing any excess material with a wet towel, but haven't concerned myself with the stains too much because I was under the impression that during the drying and usage of the oven the stains would burn off. Is cleaning up the staining necessary?

Thanks!

Mac

[rsandler]

I'm not sure, as I didn't have the same problem with stains in my first oven (and/or I had lighter colored bricks, so the stains didn't show). But in theory all the components of the homebrew mortar are supposed to stand up to heat, so I wouldn't think they would burn off. Soot stains from the fire definitely burn off, but that's different.

[UtahBeehiver]

IMHO, I do not believe the mortar will burn off. Maybe you saw a post where coals are spread out over the floor to remove cooking stains. During the heating of the oven, the dome will soot up (carbonize) until it reaches abt 700 F then the carbon burns off. The best method to remove excess mortar and efflorescence is a muratic acid/water solution. You can get muratic acid at any big box store.

[david s]

Further to your explanation Russell is the lack of hydration caused by the very thin layer of the mortar haze. Because it dries off so fast it does not have time to undergo the chemical change required for the reaction. The high surface temperature it then receives on firing probably also combined with the carbon from the soot coating is sufficient to remove it, so yes the fire alone will make it disappear. Apart from muriatic acid, dilute (10:1) hydrochloric acid or vinegar also works.

[rsandler]

Interesting--well, I think I'll still try to get the worst of it off with vinegar (HCl and muriatic scare me), but we'll see if the rest cooks off once I get there.

Slower progress on the over the past few days, due to a combination of other commitments and the 5th course being exactly as much of a pain in the neck as I was expecting. Had a good long work session on Thursday afternoon and laid 4 measly bricks (admittedly, all complicated, uniquely shaped bricks). But, I'm over the arch now (yay!) and finished the rest of course 5 in a long productive morning. Laid one brick for course 6 to sit for longer in the IT. Starting to reach the point where gravity isn't so much cooperating as grudgingly letting me get away with it.

I also bit the bullet and remade my brick cutting jig. Picked up a 18x24" sheet of 1/4" plexiglass at the big box store, and cut it down to make enough layers for the jig. Laminated the layers with CA glue, but attached the top fence layer with machine screws and nuts, allowing me to have multiple holes for different angles. Bricks now coming off the saw with much more consistent side bevels. Hopefully dialing in the angle for course 6 will be easier than otherwise, particularly as I switch to 1/3 bricks.

[rsandler]

And that's 6. Switching to 1/3 bricks definitely slowed things down, but on we go.

Thinking ahead to door-building, the notion I have is rather than fabricate a metal shell and fill it with insulation, instead I'll wrap the insulation in Nomex felt, stitch it closed with Nomex thread, and attach to a wood front either with silicone (figuring the outer surface won't get about 400F) or with screws/tacks the through the fabric from the inside. The felt on the inside surface would also serve as it's own gasket to make a good seal against the entry arch. No metal bolts to conduct heat out, no conductive metal shell either.

Will it work? No idea, but I've ordered some felt and thread, and if it fails miserably, I'll still be out less than the cost of sheet metal, and I can at least use the Nomex to fill a thermal break between the entry arch and the chimney.

[UtahBeehiver]

Interesting idea with Nomex. Will be fun to see how it works.