36" Pompeii Build Redux - This Time In CA

[rsandler]

Back in 2012 I built a 36" Pompeii at my home in Washington DC, with copious help from the folks on the forum. You can find my old build thread here: https://community.fornobravo.com/for...-pompeii-in-dc. 11 years and, by my rough estimate, some 2,000 pizzas later, we've moved back to California to be closer to family. So of course I need a new oven!

I was very happy with my old oven, so plus or minus a few tweaks I'm going to build something very similar:

• 36" floor
• Half-soldier course, then a hemispherical dome
• Semicircular arch door, 20" wide at base
• 4" Cal-Sil board underneath the floor; broken tiles or mosaic or broken glass or something under that, and weep hole in the slab.
• 3" Ceramic fiber blanket on top of the dome
• Full enclosure with a sloped roof.
• Two 4' prep table wings on either side at a 45 degree angle to the oven stand
• Rather than having the oven landing span the width of the stand, I'm envisioning a round landing right outside the door, and then have the rest of the stand even with the prep tables.

Happy to be back, and hope you all will follow along again--see if I'm any less of an idiot mason a decade later :-). Probably will be a week or two before I start work for real: still need approval from the city planning department, and in any event my shovels are still on a moving truck. Hoping to get this thing up and running sooner rather than later.

Pics are my sketchup design and some bricks laying out the outline of the foundation.

[UtahBeehiver]

It has been a long time, there have been tons of new innovations and building improvements by the members. Unfortunately they are not all in one place so one has to root around on the blog.

[rsandler]

Most of our free time has been dedicated to unpacking (house is most of the way there; my woodshop in the garage is still taking shape), but some progress on the oven today! Had a reasonably good experience with the contractor we used to do some renovations before we moved in, so decided to hire one of his crews to do the foundation for me, rather than stumbling through it myself. Ultimately a good use of funds, though it ended up consuming more of my time and attention than expected, since the concrete guy was convinced the measurements I gave didn't add up, and so initially framed the central part for the oven 10 inches too narrow. After arguing round and round for half an hour, eventually convinced him to re-do the framing anyway :-P. Sure enough, the measurements worked. The rest is up to me; we're leaving on vacation for a couple weeks (plenty of time for the slab to cure), but after we get back it'll be time to get a bunch of concrete blocks and start building this thing!

[rsandler]

And a question for the forum as I contemplate next steps: I'm planning on doing an H-shape for my stand, as pictured in the attachment. On my previous oven I never could use the whole space underneath. I plan on casting lintels front and back, with rebar running through the block cores on either side. The question: assuming I cast the lintels first, and use cement board for the tray rather than plywood, could I get away with not building a tray support? The cement board would be spanning 24 inches the short way and 48 inches the long way. My sense if that if I built a tray support for a standard "C" shape, the plywood or cement board would have roughly the same unsupported span (supported in the middle by the tray supports, rather than by concrete blocks like I'm thinking).

[david s]

The usual method is to use bond beam blocks or knockouts for the top course, supported by timber props. Likewise the support for the cement sheeting, but remember to put wedges under the props so they can be removed easily and without damaging the cast slab.

[rsandler]

Back from vacation, and inspecting the slab work. Some hairline cracks have appeared stemming from the obtuse angles--how worried should I be? I'm most concerned about the first attached picture, in the back left corner, since it seems both wider, and is traveling toward the part of the slab where the oven stand will be. How worried should I be, and is there anything I can do about it? I have a load of concrete blocks, rebar and bagged concrete scheduled to be delivered Monday...

[MarkJerling]

Back from vacation, and inspecting the slab work. Some hairline cracks have appeared stemming from the obtuse angles--how worried should I be? I'm most concerned about the first attached picture, in the back left corner, since it seems both wider, and is traveling toward the part of the slab where the oven stand will be. How worried should I be, and is there anything I can do about it? I have a load of concrete blocks, rebar and bagged concrete scheduled to be delivered Monday...

To avoid cracks like that, or at least minimize cracks like that, you need to add steel where I've drawn in on your photo.
In real terms, it's largely cosmetic, of course, but you may wish to consider steel placement in your suspended slab, before you pour that.

[rsandler]

Thanks Mark. If it's just cosmetic, I'm not overly concerned. Just had visions of the cracks expanding over time and undermining the block stand.

Current plan is to pour a suspended slab just for the oven itself, in the rectangle, and build the wings with metal studs (no need to make it bomb-proof just to hold up countertops, I figure).

[MarkJerling]

Thanks Mark. If it's just cosmetic, I'm not overly concerned. Just had visions of the cracks expanding over time and undermining the block stand.

Current plan is to pour a suspended slab just for the oven itself, in the rectangle, and build the wings with metal studs (no need to make it bomb-proof just to hold up countertops, I figure).

No worries. There's probably enough steel in your base slab for it not to come apart, so I'd think it's largely cosmetic. All you're seeing is the natural tension at internal corners.

[rsandler]

Making progress on the stand. Working East Coast 9-5 hours means I get to knock off at 2pm local, so my afternoons have been free. Only problem is it's been stupid-hot here in northern California. Got the block stand together, built forms for the lintels, and this after noon I poured the lintels and filled alternate block cores with help from my elder daughter (and from a cement mixer borrowed from my father-in-law). Those who followed my last build may remember I had a picture of her (then not quite 2) "helping" me with the gravel base under the foundation. This time she's 12-going-on-13 and was actually a huge help.

One innovation (or folly, we'll see) that I'm trying and which you can just about see in the pictures, is I put three notches in the second-to-last course of blocks to accept PVC pipes, intended as tool-holders. In my old oven I had PVC tool holders on a wooden rack in the storage area, but that wouldn't work here because of the H shape. Hoping I can have the tools above the firewood and also have the secondary storage area on the back of the oven. Or it won't actually work and I'll pull them out and do something else for tool storage--we'll see!

[rsandler]

Got the rest of the suspended slab formed up over the course of this week, and poured this afternoon, with help from the whole family. I lugged concrete bags, my eldest handled the water for the mixer, my wife and 9yo helped get the concrete pushed along the form. Doesn't quite show up in the pictures, but I set up a pallet on blocks at the back of the stand and put the mixer up on that, such that we could dump directly into the form. More or less; it was a bit of a challenge to keep it from sloshing out. I also found it challenging to work around the PVC for the weep holes; I cut them ~1/4 inch taller than the forms to make them easy to find, but in hindsight I think I should have either had them much taller, or shorter (such that they'd get buried, but I could drill them out when the forms come off).

Not the cleanest concrete ever (picture shows after screeding but before troweling; the troweling only modestly improved things). But I know well from my previous build that long term, no one will ever see the surface.

I'm aiming to pick up bricks this week and go buy the HF brick saw. Still trying to source insulation; no one local seems to carry it, and the freight charges from Distribution International et al. (or our hosts FB) are murderous.

[rsandler]

Well, I picked up 100 H.C. Muddox brand firebricks from the local brickyard yesterday along with lime and fireclay for homebrew mortar (100 bricks being the max I could safely transport in my minivan). The bricks are a little weird compared to the ones I got for my DC oven--they seem hard and about as heavy as I'm used to (weight one at 7.5 pounds), but they are cut a bit unevenly. Will make fitting the floor more of an adventure.

Also broke down and shelled out for the freight charge to get CalSil boards (Thermo 1200) and CF blanket (Morganwool) from Distribution international. I considered ordering buckets of Sairset or Greenpatch from them as well, but was dissuaded by searching the forum (said mortars not being designed for joints larger than 1/8", which I to plan to have between courses, even if I taper the sides of my bricks to fit snuggly within each course. So hopefully that will be here by the time I've got my floor ready to go.

I ended up with more CalSil boards than I really need--they sell it in boxes of 9 12"x36" boards, and you need 5 boards for a layer under a 36" oven (so 10 to make 4"). With my previous oven, I lucked out and they had an extra board around to sell me. This time I got stuck with two crates. So, I figure I'll go wild and put 6" of CalSil underneath. Overkill no doubt, but the marginal cost is zero at this point. I'd been thinking that it would be nice to have the oven floor just a bit higher this time around. But if anyone in NorCal is building an oven and needs one or two more CalSil boards, drop me a line; even with a 6" layer and leaving some extra for a door, I've still got extra!

One question for the forum: On my suspended slab, one of the rebar uprights was cut just a bit too long, such that there's an exposed end (maybe like, 2mm) sticking out of the surface. Eventually this will get covered by counters of course, but is there anything I can or ought to do to cover this to keep it from corroding?

[MarkJerling]

One question for the forum: On my suspended slab, one of the rebar uprights was cut just a bit too long, such that there's an exposed end (maybe like, 2mm) sticking out of the surface. Eventually this will get covered by counters of course, but is there anything I can or ought to do to cover this to keep it from corroding?

You'll need it 50mm down to have it not corrode, so, perhaps an easy fix would be to grind it down level to the top of the slab and then paint some waterproof epoxy over it, just to protect it until it's covered by other waterproof materials.

[AJH]

Also broke down and shelled out for the freight charge to get CalSil boards (Thermo 1200) and CF blanket (Morganwool) from Distribution international.

How much was the freight? I just got a quote from the for the same 2 boxes and it said freight would be calculated once ordered... FB Board quoted me about $125 in shipping for 36 sqft... It was cheaper for 54 sqft from DI, but they didnt tell me the freight cost.

[rsandler]

How much was the freight? I just got a quote from the for the same 2 boxes and it said freight would be calculated once ordered... FB Board quoted me about $125 in shipping for 36 sqft... It was cheaper for 54 sqft from DI, but they didnt tell me the freight cost.

For shipping it LTL, as I ultimately went for, it was a somewhat eye-popping $350. Still a little cheaper than FB for the same amount of insulation, but still steep. That said, the guy I was e-mailing with at the NorCal DI office indicated that freight charge was only for the CalSil and only because they were out of stock of it locally. If I'd been more willing to wait, he was willing to add some to their next stock truck order for no freight charge, but that would be "a few weeks". Decided I'd rather spend the money than deal with the uncertainty/delay, especially since the normal weather pattern in my area is that it starts raining some time in October and doesn't really stop until March (plus or minus drought years). Gotta get my dome closed up before the rain starts, and can't get much further until I've got floor insulation, I figure.