36" in Seattle, second oven

[david s]

Yeah, I've read a lot about the long damp curing times involved. I had similar issues with the concrete slab and hearth of the first oven of course, and the dome itself given the homebrew mortar. I had noticed the "burnout" fibers mentioned in some of the conversations, but like I said, there are so many of these mixins involved, that I desperately wish someone in the know would draw up a document on castable ovens, something comparable to the Pompeii manual. I'll just have to start going through the discussions very carefully. Where do I learn about burnout fibers? Google sends me to https://highwaterclays.com/products/burnout-fibers which has a photo that resembles something I've seen in a forum post or two, but golly, I really don't know what I'm doing here. Isn't there any documentation? Yikes!

No, The only documentation on homebrew castable is in the thread builds here. This is because I am the initiator of the homebrew castable method cast in situ over a sandcastle dome method.
Not being sure how it would work out, I advised two interested homebuilders here way back in around 2010. As it turned out those two ovens are still performing well so I've continued advising others here of a simple, fast and cheap way to build a home oven.
I don't have the time or inclination to write a book on the subject, but happy to field any questions. I suggest you read as many of the cast builds that you can find here.
Those are the correct fibres to use, you don't need much, but they need a lot of mixing to disperse sufficiently. As well as burning out they also do a good job of holding the mix together and eliminating slump cracks, but don't add additional strength.

[kebwi]

Has anyone ever embedded wire mesh in the cast wall?

[david s]

Very difficult to get the mesh sitting in the middle because of the compound curve of the dome. It also runs the risk of delaminating where the mesh is. Chickenwire is no good because the temperature of the inner dome will melt the galvanized coating and it will rust. I have seen one that used bronze mesh. Far better to use random fibres in the mix. The industry standard is to use melt extract random fibres (stainless needles) I use as needles, basalt fibres and AR glass fibres. Most cast oven manufacturers don’t use any reinforcing fibres. If they did they would be advertising that they do.The burn out fibres in proprietary castable refractory are already included in the product.

[kebwi]

Ok, thanks. Just trying to think through all of this. I still need to go back through the castable threads and build a list of these additional materials, the various structural add-ins.

Oh, another question I remember arising in my mind: the homebrew recipe for casting is often described as containing "clay", just "clay". In many places it isn't specifically described as "fireclay", which of course is an integral component of homebrew mortar for bricks. But, may I assume that the homebrew recipe for casting is also exclusively fireclay? I mean after all, it's a refractory product. That's the whole point, so I assume cast ovens are only and always built with "fireclay" for the clay component of the recipe. Right? Seems obvious but since it is often just called "clay" in some threads, I want to make sure I buy the right materials.

[kebwi]

One problem with confining all my questions to this thread instead of starting new threads for each question, is that I feel like this is just a conversation between you and me. I feel like no one else will find this thread or contribute to the discussion. I don't mean to lean on you so heavily.

Has anyone ever built a cast oven with a brick arch (including the inner arch, not just the decorative facade) and gallery? Just kicking ideas around my head. I'm wondering if I can make a brick arch more easily than casting it.

[david s]

I can see no reason why a brick arch and a cast dome would not be compatible.
I do go out of my way to refer to the clay content in homebrew as just clay rather than fire clay. The reasons are two fold, firstly because of the temperatures involved at oven cooking any clay should be sufficient, although avoid Bentonite as its extremely small particle size leads to excessive shrinkage. Secondly there is confusion about the term fire clay because in the bricklayers game it is just cheap powdered clay to add to a mortar to impart more stickiness. To a potter fire clay is a highly refractory clay, lacking fluxes, (primarily iron oxide) making it resistant to very high temperatures our ovens would never see. Fire clay is generally an American term for bricklayers clay and generally not used as such in Australia and the UK
After complaining to Cement Australia about this point they renamed their product and it is now labelled Brick Layers Clay.
Theclay needs to be powdered as clumpy clay in a plastic state does not mix easily. The high proportion of clay in homebrew does impart plenty of stickiness which is an advantage, but also produces excessive shrinkage. Normally 7% is about the upper limit as a mortar addition. The homebrew clay content for the 3:1:1:1 is 1/6 (16.7%)
If building over a sand mould there is probably enough give, but I now halve the clay content for both mortar and castable use to reduce shrinkage giving a new ratio of 3:1:1: 0.5
I’m not sure I’ve done the right thing, but it seems to work and has cured the shrinkage problem.

[kebwi]

I'll have to price around, although I don't believe I thought fire clay was super expensive. But nevertheless, if I find some other form of clay available, something not specifically refractory and potentially a little less expensive, I think you're saying there would be no risk in going with that option instead.

Thanks.

[Gulf]

david s, We have the same problem here with distributors misrepresenting their product. A friend of mine called me on the phone while gathering his supplies. He said that they had the "fire clay" on hand. I asked him the price and he said "$125 a bag. I told him to leave it. It was actually a preblended calcium aluminate mortar. He picked up the actual fireclay later at a brick yard that I recommended for $22 a bag. That was during the supply issues of COVID. It had jumped up from $16 a bag from just a few weeks before.

kebwi, JRPizza may be able to lead you to the right stuff from the right supplier. He's from just a few miles North of Seattle.

[kebwi]

Going back to thin brick domes for a moment. I realize that the challenge is basically building a segmental dome, the dome equivalent of a segmental arch, in which extreme lateral stresses are put on the lowest courses, such that the primary point of failure would be having the base of the dome slide outwards and with insufficiently thick walls that the mortar itself would not adequately glue the dome together against such slide-out forces (I get the impression that few ovens actually confine a catenary to their middle third in true self-supporting form, but rather are truly relying on mortar adhesive strength to overcome a lack of true self-support; hence the prescription for thick walls and wide mortar surfaces).

This of course leads to the proposal of buttresses when one is referring to segmental arches. Buttresses aren't a topic that come up so much with domes, but I do remember seeing one or two threads in which people poured a concrete ring around the base of their oven. Obviously I couldn't pour ordinary concrete as a buttress to the lower courses because that would be a heat sink, but this line of thought led me to the idea of pouring a vermicrete or perlcrete buttress ring, possibly with a ring of rebar or mesh embedded in it.

It would only need to come up as high as the lowest two courses, give or take, where those lateral forces are pushing the foot of the dome outward, and the ratio could probably be somewhere between that prescribed under a floor (5:1) and that which works over a dome (upwards of 10:1). I was wondering if I could pour a 6-in thick (or whatever thickness makes sense) perlcrete ring, in the 8:1 range (a compromise of buttressing strength and heat sink resistance), from the hearth, up past the insulating subfloor, past the brick floor, and up to the top of the bottom two (give or take) brick courses, i.e., to whatever height the angles are going to push outwards, about 12" high in total. Above this buttressing wall I would then resort to blanket insulation as per usual design, on the argument that the top of the oven both doesn't need buttressing but does need greater insulation since the top portion heats up so much more aggressively.

Would this design enable a 3-in thick brick dome to survive?

I suppose another idea is to forgo the blanket and literally encase the dome in perlcrete, effectively creating a fully top-loaded dome, which of course is a classic way of protecting non-caterinary arches going back to the Romans with their generally semicircular arches.

This of course would have some thermal implications, either with just a lower ring or with full encasement. The perlcrete layer, combined with the 3" brick, would represent an average thicker thermal mass then the same 3" wall wrapped in blanket, but the question is whether this design enables a thinner wall that heats up faster than a 4-1/2" wall but is still structurally sound due to a buttressing ring or full encasement.

Just curious.

[kebwi]

Thanks for jumping in Gulf . I have felt bad that david s is fielding this entire discussion. I wish it was more of a group forum as I bounce my questions off the community. I don't want to lean on Dave too much.

Having been very focused on a brick oven for my second oven until just a few days ago, I have yet to go through the cast oven threads to carefully pull out all the scattered descriptions of new materials I need to come up to speed on. The clay question mentioned above was one, but I need to look into -- well I can't remember -- I know SS needles came up, so I understand what those are now, and there's this business of burnout fibers, which I confess I still haven't Google at length yet, and then there's various other terms I've lost track of and can't remember. I think there's something called..."AR something or other?" But honestly, I think I saw three or four other materials mentioned throughout the various threads and I've lost track of them because I wasn't in a note-taking mode when I originally perused the archives -- because I was honestly really focused on a brick oven, and as you can see from my last message, I'm still enamored with brick. But at some point here, I need to properly "research" cast ovens. I put that in scare-quotes out of frustration that each new cast oven builder has little choice but to scrape this wisdom out of the scattered message forums in lengthy search instead of reading some overview document that summarizes the options.

But having since learned that Dave pioneered these cast designs (I didn't understand his role at first), I now realize that my frustration comes down to an unintended burdensome request on Dave who shouldn't feel obligated to put in such effort.

To save Dave from having to do that on his own, I recommend we start a community document for cast ovens. It could be a shared Google Doc for example. We could, as a community, draw up an introductory and instruction document for cast ovens so new-comers don't have to approach the problem the way I am attempting at the current time. I'm the very last person who should own such a project however since I admit to being an absolute newbie at cast ovens. But whatever. In the meantime, I'll comb through the forums and figure this out -- or build a brick oven anyway. I still haven't decided.
Cheers!

[Lotus19]

Hi Kebwi,

I'm in your neck of the woods and just finished my cast oven, using the homebrew mix: https://community.fornobravo.com/for...8115-pnw-pizza


I can try and answer most of your questions, but I'm sure the other cast-style builders will happily jump in with answers, advice, tips, etc...

Joe

[kebwi]

Gosh Gulf , I'm on the north side of Seattle too. I think JRPizza and I must be really near each other. We should get together sometime.

[kebwi]

Thanks Lotus19 . Looks like you're just across the water from me. I'm in Shoreline.

[david s]

Thanks for jumping in Gulf . I have felt bad that david s is fielding this entire discussion. I wish it was more of a group forum as I bounce my questions off the community. I don't want to lean on Dave too much.

Having been very focused on a brick oven for my second oven until just a few days ago, I have yet to go through the cast oven threads to carefully pull out all the scattered descriptions of new materials I need to come up to speed on. The clay question mentioned above was one, but I need to look into -- well I can't remember -- I know SS needles came up, so I understand what those are now, and there's this business of burnout fibers, which I confess I still haven't Google at length yet, and then there's various other terms I've lost track of and can't remember. I think there's something called..."AR something or other?" But honestly, I think I saw three or four other materials mentioned throughout the various threads and I've lost track of them because I wasn't in a note-taking mode when I originally perused the archives -- because I was honestly really focused on a brick oven, and as you can see from my last message, I'm still enamored with brick. But at some point here, I need to properly "research" cast ovens. I put that in scare-quotes out of frustration that each new cast oven builder has little choice but to scrape this wisdom out of the scattered message forums in lengthy search instead of reading some overview document that summarizes the options.

But having since learned that Dave pioneered these cast designs (I didn't understand his role at first), I now realize that my frustration comes down to an unintended burdensome request on Dave who shouldn't feel obligated to put in such effort.

To save Dave from having to do that on his own, I recommend we start a community document for cast ovens. It could be a shared Google Doc for example. We could, as a community, draw up an introductory and instruction document for cast ovens so new-comers don't have to approach the problem the way I am attempting at the current time. I'm the very last person who should own such a project however since I admit to being an absolute newbie at cast ovens. But whatever. In the meantime, I'll comb through the forums and figure this out -- or build a brick oven anyway. I still haven't decided.
Cheers!

Don't feel bad about burdening me. Because of my advancing years I reckon I've probably only got another 5 years of oven building in me. Unloading, mixing, moving heavy materials and castings is probably not on the agenda at 80+ I came to this great forum in 2007 and received lots of help and researched lots of information, so happy to give back knowledge. Folk here, unlike many industries where secrets are kept rather than shared, are only too happy to get others back on to the joys of wood fired cooking which helps people link with history, stepping off the grid and visiting a primeval method of cooking using carbon already in the system. Isn't fire magic? (I'll step off my soapbox now).
I agree that perhaps a section on the forum that could provide more comprehensive info in one place would be good. Perhaps the Mods could create some sticky threads under cast ovens.

I don't feel inclined to produce a large document on the subject, mainlly due to time constraints, but more than happy to help out folk on an individual basis.

[kebwi]

What did you think of my weird perlcrete buttress ring or perlcrete full encasement (no blanket) proposals for building a 3" thick brick oven? No hope?