36" in Seattle, second oven

[kebwi]

I recently posted a few questions on a per-question basis in seemingly topic-relevant subforums, as separate threads each, instead of posting them in a single over-arching, per-user thread -- and was then told that isn't how the forum works anymore. Instead, everyone confines their posts to a single thread that is all about their oven, or something to that effect. Admittedly, I built my first oven in 2009 and haven't been active on the forum for thirteen years, so I suppose I lost track of how the forum is used now. So be it. So, to that end, I suppose this thread will serve as the single Q&A and discussion thread where I will post all my messages. I'm not sure I chose the correct forum since this one is named "photos" and I don't have any photos of my second oven, which may never get built anyway, but I had to pick a subforum, so here I am.

If I build a second oven, it would be another 36", like my first oven. I would probably use the same curvature profile, but discard one of the two stretcher courses, effectively dropping the ceiling height of the dome from the first oven's height of 16" down to 13.5". Corresponding, the inner arch's height would drop from 11" to 8.5", and the design I currently have in mind would shrink the inner arch's width from 22" to 21".

I'm planning on cutting bricks into thirds, and using them to build a 3" thick oven. 4.5" is the Pompeii standard of course, and 2.5" (face on bricks) are highly discouraged for structural reasons, but I found the heat-up times of my first oven frustrating, so I want something with thinner thermal mass. I'm inclined to try bricks cut into thirds, yielding 3" walls. As with my first oven, I'll wedge-cut the bricks so they form a pretty tight dome with small mortar gaps. It should be impossible for the bricks to "fall in". The question is whether dome actually fails of course.

The arch design is radically different from my first oven. My motive is to keep the arch work minimal, involving as few bricks and cuts as possible, so it would consist of nearly whole bricks, instead of lots of little bricks, facing along the entry axis, along their 2.5" dimension, instead of end-on as is common in some designs. In this way, the thickness of the inner and outer arch courses would be 4.5", with a 1/2" or 1" door seal (I have designs for both seal widths at the moment. Between the inner and outer arch, in the "gallery" area beneath the flue, the walls probably wouldn't be brick, but rather poured perlcrete, parged with homebrew. This would provide a 6" insulated thermal break, a seeming evolution in new ovens since my first oven, between the inner arch and the outer facade...although I suppose heat would still diffuse through the brick floor. I haven't seriously considered thermal-breaking the floor yet.

I would use two layers of 2" (4" total) TaoFibre board under the floor, which as far as I can tell is identical to InsBlock. The dome will be covered in a few inches of ceramic blanket depending on how far it goes before I run out. I'll pour weep holes in the hearth, as per design evolution since my first oven. The flue will be 6" double-walled pipe. I have three 3' sections, so final heights could be 3', 6', or 9'.

I'm undecided on an outer layer. It could be a few inches or percrete as an igloo, finished out with weather-proofing, or just a big 'ol box filled with loose perlite...or perhaps both: ceramic blanket -> perlcrete igloo -> loose perlite fill. Given Seattle's rainy weather, I'm not sure I would trust any igloo design to be adequate. I suspect that even if I built an igloo, I would probably follow it up with a "carport" style roof anyway (i.e., perhaps something open-sided, but nevertheless a proper roof overhead. I don't know. None of that is decided yet. Another modern development in oven designs since my first oven appears to be a moisture vent in the dome so that water (and steam) can escape and the dome can dry out more easily -- and avoid cracks from contained steam pressure. Sounds cute, so maybe.

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[kebwi]

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I'm most hung up on the structural support question actually. I would like to achieve two challenging goals if possible: (1) slight movability (just the ability to gently roll it around my large patio from one place in my yard to another as needs and desires may require from time to time) and (2) modular, nonpermanent deconstruction so that whole thing can be relocated, or at least demolished, at some future time with relative ease. I lost my first oven when I sold that house and moved. I slaved over it for eight months and continued to work on its final construction for more than a year, and when I moved I lost the whole thing forever. I'm very nervous about building another permanent yard fixture. I want to be able to put the whole thing on a flatbed and take it with me, as unlikely as that may seem.

Toward the first goal, slight movability, I have researched sturdy wooden structures and welded steel structures. I understand the arguments against wood, but I have no experience or skill with welding and have not found a second-hand cart or table that seems satisfactory. I did find impressive (both strength and cost) casters (https://www.amazon.com/dp/B0BHF3H86S) so I think I could support the weight on the wheels, perhaps six or eight wheels if four were deemed too risky. I just don't know how to built the actual structure itself since wood is discouraged and welding is utterly beyond my skillset.

Alternatively, I could give up on movability, but still emphasize modular deconstruction. This would require that the hearth not be bonded to the stand with rebar that crosses the boundary between the two. Likewise, it would help if the stand was multiple pieces (legs, in effect, concrete pillars of stacked blocks, or interlocked three-half-block runs, and possibly "L"s at the corners). I'm strongly leaning toward 6" wide blocks instead of 8" incidentally, to reduce total weight and total material/labor investment. So I envision stacks of blocks, either straight (but not long walls) or L-corners, filled with rebar and concrete, but not bonded to the hearth (and not bonded to the patio either, by way of plastic underneath during core-filling). To connect the hearth and the stands, I would both "dip" the hearth pour down into the stands and I would bolt the hearth to the stands with corner braces. First, I would cover the tops of stands (the tops of the concrete-filled pillars) with plastic before pouring the hearth so they don't bond together. To assist the hearth in "sitting" on the stands without lateral shift (nigh but impossible, but nevertheless...), I would create depressions in the plastic dipping down into the tops of some of the concrete blocks, supported from underneath by some scaffolding, a cup in effect. The hearth pour could then "spill" into these depressions an inch or two. In this way, the hearth would have "feet" that sit inside the holes of some of the stand blocks. The hearth could not shift laterally (short of a major earthquake), but would still benefit from further protection against sheering over and falling in that fashion. So to further strengthen this structure, I would use heave-gauge Simpson-style corner braces. I would drill through the concrete block walls and pass 1/2" bolts or threaded rod through. Then I would put PVC plugs in the hearth during the pour, much like the weep holes under the oven, such that when finished, the hearth would have holes to drop a bolt through to the corner brace underneath. If I inset the PVC with a larger head at the top (so the cross section of the hold is T-shaped), the bolt head could then fall "into" the hearth 1/2" to 1" such that the hearth remains flat and flush (I could then plug these holes up with something leak-resistant, some pourable goo that could be dug out when deconstructing the oven, I don't know). If further strength was required, I could also bolt either 2x4 or metal strip diagonal cross-braces between adjacent stand legs. Since the whole thing would be bolted together, it could then come apart if needed, and a pallet jack, forklift, or crane could lift the hearth and oven straight off the stands. The stands could also be independently removed of course, especially if I would put plastic under them before pouring their cores so they don't bound to the patio.

But, this design is starting to get pretty complicated: independent concrete pillars of block, hearth "feet" that pour down slightly into the tops of the pillars, corner braces, mildly complicated hearth plugs for bolts, drilling several large holes in concrete blocks (which I imagine isn't much fun), and 2x4 or metal strip diagonal cross braces. This is getting out of hand just to achieve modularity and possible, potential hearth-and-oven removal at some indeterminate future date -- but recall my motivation. I have already lost one oven by having to leave it behind, so I am really worried about this issue.

All of this leads to my first question. During my failed search for metal tables to repurpose as a support structure, I found some nice steel table legs I could use to build a "concrete table", i.e., the hearth: https://carolinalegco.com/collections/metal-legs. Of their available styles, I'm particularly enamored with the four independent legs and the H-block leg-pairs. I have asked about the sizing and they say the tubes are 2", 14-gauge. I feel like 14-gauge is a little thin, but I'm out of my element on such matters. I really don't know. When people have welded their own metal oven stands in the past, what gauge steel were they using for those stands? Would these table legs work for this project? What if I bought two sets of legs of either style, i.e., eight of the individual legs or four pairs of the H-block leg-pairs)? That's getting kindy pricey but first I'm exploring structural options. I'm inclined toward the H-block pairs because they are already partially cross-braced of course. The individual legs would allow me to spread them out or position them more freely of course, but at the expense that they are a little "stilty" until I find some way of attaching cross braces to them (without any welding since I can't do that in any practical way).

Do people here with knowledge of metal know if 2" 14-gauge square tubes would hold up a hearth and 36" oven? Obviously, I can run the numbers to estimate the total weight, but we all have a ballpark notion of these ovens. We've been familiar with them for fifteen to twenty years now. So even without grinding out all the calculations, what do you think? Photos in this site's forum suggest that legs like these are sufficient to the task (i.e., similar in appearance to metal frames elsewhere in the forum), but I don't know if those other builds used heavier gauge steel or larger tubes. Would four legs be sufficient or would eight be necessary, despite the cost? Or is this (2" 14-guage steel) just not a viable solution and I should go back to the concrete block design (thereby all but forgoing within-yard movability, although still possibly modular for eventual long-distance travel at the cost of significant design complexity)? One advantage of the pre-made legs shown on that website in the previous paragraph is that construction would be a piece of cake. I would just put PVC plugs in the hearth to line up with the leg mounts, pour the hearth, and then bolt it all together...again with the PVC inserts "widened" at the top to allow the bolt heads to drop down flush with the hearth. It would be super simple to construct a stand and hearth in this fashion. But I just don't know if this is a sufficiently strong design.

Thanks.

[david s]

What you are trying to achieve is far better suited to a cast design for two main reasons. Firstly brick builds require 4” thick walls to achieve structural integrity. This requirement has been proved for hundreds of years and when taking thermal expansion into consideration is even more important. Departing from a hemispherical form increases the sideways thrust on the walls nearer the base of the dome which requires either steel bracing or buttressing. A cast dome does not need these requirements and can therefore be made thinner and consequently lighter. Most cast ovens go for a 2” thick dome.
The second problem is mobility. Many mobile brick builds simply fall to bits because heavy unitised brittle material does not like to be transported. Some cast oven manufacturers offer one piece cast domes rather than multi piece ones specifically for mobile ovens.
Whilst you are only planning limited mobility these factors, particularly the weight still apply.
Because of a high centre of gravity, the footprint of the stand needs to be fairly big and the diameter of the wheels, particularly if the terrain is not perfectly smooth, need to be large.

[kebwi]

Hmmm, ok. Good points. It had slowly started to cross my mind to look into the cast ovens. I admit, I was almost entirely unaware of the concept. In 2009 when I built my first oven, I don't recall any discussion of home-cast ovens. There were cast ovens you could purchase, but I don't remember people just making their own. Now I see there's quite a bit of that on the forum, but I admit I haven't looked at it very closely because I was in a brick state of mind. I just assumed cast ovens were some other thing I was uninterested in. But like I said, in the last day or two I started wondering if a cast oven would be more suited to my preferences.

What about the other question, the 2" 14-gauge steel. Would four of those hold up a four inch hearth, a brick floor, and either (1) a brick dome (as per your points, 4.5" thick and permanently installed) or (2) a cast dome (which would be significantly lighter weight due to its thinner walls? Would it hold up either of those ovens, or is 2" 14-gauge square tube just not up to the task?

I guess I'll scrap my notions of a 3" dome. This doesn't change the fact that I found my first oven to be exhausting to fire up. I just didn't want to use it, to be honest, feeding it wood for two hours to make pizza. I was hoping to go with a thinner dome so it would homogeneously saturate with heat faster, but I guess a cast oven is the only way to accomplish that goal.

Thanks.

[kebwi]

I see posts on other castable threads saying they still take 2-2.5 hours to heat up, despite being 2" thick. Is a faster heat-up time actually not an advantage of castable ovens despite the expectation that a 40% thick wall ought to imply a 40% heatup time (assuming linear heat diffusion)?

I am not initially excited about building a cast oven.

1. I don't want to learn a whole new skill for the second oven. I know how to build a brick oven as I've done it before and I'm looking for a simple and quick second oven, not the huge project my first oven was with all the initial learning involved.
2. I consider brick ovens more aesthetically pleasing, viewed inside of course.
3. The cast ovens on this forum appear to be nearly hemispherical in most cases, cast over tall and round sand forms from what I can see, but I want a lower, flatter pizza oven, not a bread oven.

My first oven took eight to twelve months to build, depending on what state one calls finality, and I'd like this one to be a simpler, faster project. I know how to build a brick oven at this point. I can cut very tightly wedged shaped bricks that will have no way to fall in from the ceiling -- but I fully understand the other issue with self-supporting domes: that the overall shape of the dome profile of ovens in particular is problematic due to their lower, flatter, non-catenary shapes (not that any cast ovens on this forum are low and flat either, but I guess the fiber/needle inclusions enable cast ovens to be thinner than brick, if not necessarily lower or flatter apparently). I'm pretty technical, so I understand this catenary argument about dome structures -- but I am a little unsure why it is more problematic with brick than cast. Shouldn't cast ovens push outwards and buckle or collapse in similar ways, thereby requiring thick walls too? Apparently not, but I don't understand why. They need to contain the catenary in their middle third as well, right?

But as observed above, if people report that 2" cast ovens won't heat up any faster than a 4.5" brick oven anyway, then what's the point? That's what I thought I read.

I found the heat-up times of my 4.5" oven to be a significant detractor from using it. It had 3" of Insblock under the floor, 3" inches of loose InsWool around the lower sections, increasing to 6" of loose InsWool at the apex, all surrounded with several inches of 10:1 vermicrete. And yet I had to slavishly feed it wood for 2-3 hours before I could use it. It was obviously adequately insulated.

When I started seriously considering a second oven a few weeks ago, I did some casual math in my head and -- assuming heat diffusion through brick is essentially linear -- I figured that if I made a 2.5" oven (face-on bricks) or 3" oven (bricks cut into thirds long-ways) it would heat up 1.8X or 1.5X faster respectively (55% or 67% the time of my original 4.5" oven). But even if thin brick ovens are discouraged, it doesn't seem like people's experience with 2" cast ovens is much faster than my 250% thicker brick oven anyway. I should be reading that people are cooking in their cast ovens in 50-80 minutes (40% of 2-3 hour brick ovens), but I don't think that's what I've seen in the forums (maybe I should go through them again; it's a lot of forum hunting to find specifics like this buried in a 15-page thread).

Is there any version of these ovens, brick or cast, thick or thin, that is cookable in 60-90 minutes, or do these ovens just not work that way?

If anyone reading this thinks I've misunderstood cast ovens and they actually do heat up faster (presumably due to their thinner walls), feel free to correct me. I've been reading the posts, and I thought I saw people reporting heat-up times that seemed comparable to brick ovens. Did I misunderstand something?

And can cast ovens be made with a pizza oven profile (lower and flatter) or are they always cast over a nearly half-sphere, as shown in most of the forum posts. I want a pizza oven (that might occasionally be used for bread), not a bread oven (that might occasionally be used for pizza). Why are all the cast ovens on this forum so tall and round?

And why, technically, can a cast oven be thinner? The same catenary math applies. Even though they don't have to contend with individual bricks falling out, the force vectors pushing down and out through the walls of the dome are the same. They should buckle or collapse in the same way as a brick oven when they don't contain a catenary in their middle third, so why are they more tolerant of thinner walls?

I also asked in an earlier message above if people think those metal legs I found online will hold up an oven: 2", 14-gauge steel square tube. Do any engineers in the forum have an opinion on that question?

[david s]

You've posed a number of questions so I'll do my best to answer them.
Both fire brick and castable refractory have about the same thermal conductivity, although some may argue that the denser high duty bricks have more, the difference is marginal.(Most builders use low or medium duty bricks because the high duty ones are the most expensive and hardest to cut) This means that because heat will travel at around the same rate through the material a thinner dome will arrive at pizza temperature a bit faster. The limiting factor is how big a fire is maintained to achieve the result. Unfortunately too rapid a heat rise is damaging to both brick and refractory with micro cracking that won't be visible taking place due to uneven thermal expansion. Some owners will boast that they can achieve pizza temperatures very fast by getting a roaring fire going from start up by using a draft door. This can be quite damaging in my opinion and is akin to a potter firing a kiln at full blast from start up. This is something no potter will do because they know the consequences ti their wares is they do. Brick and refractory are less vulnerable than pottery ewares but the same principle applies. The standard for potters is 100C/hr in the vulnerable zones of ambient to 350C and also from 500-650C. Most oven owners will ramp up at around 300C/hr. The usual practice is to start with a small fire, feeding it slowly where it takes as much fuel as the fire requires, to arrive at filling the chamber with flame by around one hour. I once had occasion to fire as rapidly as possible with my mobile oven and got the whole dome white in under an hour, but usually it takes one and a half hours and if I have a large function to cater for I'll continue for two hours before beginning cooking pizzas. My oven is 21" internal with 2" thick 3 piece dome. Another fallacy is that a smaller oven will heat up faster than a larger one. The reason it doesn't is because the chamber of a small oven is simply smaller therefore the fire it contains will be smaller.

Some brick builders have gone with thinner domes only to find that the joints fail because as history has shown even brick construction walls require 4" wide joints. You don't see walls made with bricks on edge (3") because they're likely to fail. The extra problem of thermal expansion throws further problems int the structural integrity. The lack of, or vastly reduced number of joints in a cast oven allows both thinner walls and departure from a more stable form (lower dome). Most cast oven manufacturers have designs, including Forno Bravo kits, that have relatively high walls and flatter domes.

If your main goal is fast heat up then you should consider a stainless insulated oven which will heat up really fast because of the very thin highly conductive material. Their drawbacks are that they also cool off really fast so have no thermal mass, apart from the cooking floor, so retained heat cooking is out. Being quite light they are also suitable to be moved around.

Catenary arches (the arc described by a hanging chain and then inverted) are the most structurally sound arches, so much so that they do not require bracing or buttressing. Unfortunately they are not suitable for ovens because once the height becomes less than the width, the angle at the base creates an angle producing unusable space.(see attached drawing)
I actually love catenary arches, see my structure starting here. (Jump to #32 to get to the catenary part)

https://community.fornobravo.com/for...kiln#post14564

[kebwi]

Thanks again, as always, for your depth of responses. That's an interesting point that cast ovens might heat up faster do to lower density than brick. I could see that going both ways actually: less thermal mass is literally fewer molecules to heat up, so that would go faster, but lower density would have less efficient heat convection through the wall before achieving equilibrium, so that would go slower -- but if you say the tradeoff tilts in favor of the less dense material, I understand your point.

I was not one of those under the impression that small ovens heat up faster. It made perfect sense to me that the relationship between the thermal mass you are trying to heat up and the size of the heat source you can build to heat it up operate in tandem. But thanks for restating it. I get it.

Okay, so the reason cast ovens can withstand thinner walls isn't that they contain the catenary within their arch (as, surely, they don't!) but because the weakness of a brick dome is at the gaps between the bricks. A cast dome is, to some extent, one gigantic brick (or a very small number of giant bricks merged along a few long expansion joints between sections). I guess I understand that. It's disappointing that this is as strike against thin brick ovens, but I see what you are describing.

Not that I think the following idea could be achieved with a conventional tile saw, but I wonder if one could cut bricks with a tongue-and-groove shape so that each course "locks" to the course below it, such that the gap between them can't so easily "fold" outwards with a resulting buckling and collapse. A square tongue-and-groove would be very hard to cut. The tongue would be feasible (four simple cuts), as would be the two sides of the groove, but the final cut along the bottom of the groove would be nearly impossible to achieve. One could approximate a tongue-and-groove by cutting V-shaped tongues and grooves instead of squares (so that one edge is V shaped and the other A shaped). It wouldn't have the angular resistance to buckling of a square tongue-and-groove, but it would be much better then the flat-faced join of simply mortaring bricks together course over course. Anyway, that's kinda crazy, but it's an idea that crossed my mind.

I agree with you on the elegance of catenaries. I've always been fascinated by arches. Romans discovered hemispheres, which are pretty self-supporting especially when loaded from above, such as when incorporated into a wall, but my other ancient culture of fascination, the Mayans, never discovered self-support arches. The best the Mayans came up with is a corbeled arch (https://en.wikipedia.org/wiki/Labna). So I'm pretty aware of both the theory and the history of arches. And yes, I recognize that unfortunately, the thermodynamic properties of ovens and baking are in conflict with the purest catenary arch forms.

Anyway, I'll consider my options.

Why is this less problematic with segmental entry arches? Lots of ovens are designed with barely-curved arches that land on vertical walls at the sides. Why isn't the risk of such arches collapsing of much concern, especially with the flue pressing down on it? No one worries about this issue with entry arches and yet it is practically a prohibition on domes. What's the difference?

[david s]

"cast ovens might heat up faster do to lower density than brick." no, re-read my post, I said brick and refractory have the same thermal conductivity. The higher the conductivity the faster the heat up, as in stainless ovens. The density of any given material will lead to an increase of its thermal conductivity.

Regarding the tongue and groove joints, which would be almost impossible to achieve between bricks cut with a saw, most cast ovens go with half lap joins at the junction between sections. In my builds I employ a tongue and groove join idown the middle in the two piece floor sections that leave only one join which has proved sufficient to provide for thermal expansion while only leaving one join to catch a peel on.

The reason the outer arches are less problematic is because they are at a lower temperature being further away from the fire. I have seen enough cracked outer decorative arches to convince me that an expansion joint between the dome and gallery or gallery and dome is important to eliminate stresses from hotter expanding inner oven parts on to the cooler oven parts.

[kebwi]

Oh I see. I did misread it.

But, my frustration from above is unresolved. I felt that my perusal of the forums revealed people's experience with cast ovens as heating up in two hours, give or take. Mathematically, cast ovens should clear in literally 44% the time of brick ovens (2" vs. 4.5"). If brick ovens require 2-3 hours, cast ovens should be ready in 50-80 minutes. But my point is that I don't see reports like that in the forums. Did I miss the relevant messages and posts where builders of cast ovens actually did acknowledge that their 2" cast ovens were clear and hot in an hour?

My question about outer arches wasn't about cracking, it was about dome collapse. You have emphasized that a shallow catenary pushes outward at the base of the dome (which would conceptually "slip out" and collapse). Why don't segmental entry arches have the exact same problem?

[david s]

Oh I see. I did misread it.

But, my frustration from above is unresolved. I felt that my perusal of the forums revealed people's experience with cast ovens as heating up in two hours, give or take. Mathematically, cast ovens should clear in literally 44% the time of brick ovens (2" vs. 4.5"). If brick ovens require 2-3 hours, cast ovens should be ready in 50-80 minutes. But my point is that I don't see reports like that in the forums. Did I miss the relevant messages and posts where builders of cast ovens actually did acknowledge that their 2" cast ovens were clear and hot in an hour?

My question about outer arches wasn't about cracking, it was about dome collapse. You have emphasized that a shallow catenary pushes outward at the base of the dome (which would conceptually "slip out" and collapse). Why don't segmental entry arches have the exact same problem?

Theoretically they do. The reason Roman arches remain stable is that they are buttressed at their sides by another arch or massive buttresses at the sides. Check out the Colleseum which has a collapsed arch at the back so the arch closest to the damage is no longer buttressed by an adjacent arch. Slowly a chain reaction takes place with the arches collapsing like dominos. There is now massive repair on the ends with reinforced concrete to support the ends. I think most oven arches get away without the buttressing or bracing because they are small, but there are reports of failing arches where extra weight of brick chimneys is placed on top of them. Regarding dome collapse, because the dome is three dimensional rather than an arch which is two dimensional there is far more support and the dome cannot therefore collapse. The outer arches of the gallery and outer decorative arch are far more vulnerable being two dimensional.

The temperature at the inner face will always be greater than that of the outer face and the thicker the walls the bigger the difference. Therefore thin walls will reach a heat saturation point faster than thick ones. Operators firing regimes will also vary considerably so comparisons on time taken to pizza temperature are difficult. Also other factors like ambient temperatures, quality and amount of insulation, moisture content in the oven and insulation layers as well as the moisture and type of wood used make comparisons even more difficult.

[kebwi]

Ok. I started reading the cast oven threads a day or two ago. I'll consider it. Is there any formal instruction on this process, like the Pompeii manual or does everyone just deduce it piecemeal from the forum discussions? I'd love to find a single document that walks through the theory, design, issues, etc. And then presents and teaches about the various materials, such as the multiple options for structural mixins, etc. I'm weary to just cobble my understanding together by reading threads. I'd prefer something a little more centralized and formalized... Just like the Pompeii document.

[david s]

No there's not, but as nearly all oven manufacturers use dense castable refractory and that is easily obtainable, although expensive, it is a quick build and easy enough to do a one off build. If cost is a problem the castable refractory can be replaced using the homebrew 3:1:1:1 mix (possibly not as durable as castable refractory, but members who've built them report good longevity).
Departure from a hemisphere form is far less of a problem than for a brick build as this thread discusses. The casting strength can be enhanced with fibres although most manufactured ovens I've seen don't, so it's certainly not mandatory. All other aspects of the build are much the same as a brick build.

[kebwi]

Oh I'm definitely of the homebrew culture. I used homebrew for the mortar of my first oven. Well, given that there appear to be a variety of structural mixins to choose from, I guess I'll have to go through the cast oven threads carefully and note the various options benefit/tradeoff discussions surrounding them.

Or I'll just build a brick oven. I haven't decided yet.

Thanks.

[david s]

Oh I'm definitely of the homebrew culture. I used homebrew for the mortar of my first oven. Well, given that there appear to be a variety of structural mixins to choose from, I guess I'll have to go through the cast oven threads carefully and note the various options benefit/tradeoff discussions surrounding them.

Or I'll just build a brick oven. I haven't decided yet.

Thanks.

If you go the homebrew route as you know it's cheap and pretty user friendly, however there are two drawbacks
1. You need to add the burnout fibres which are already contained in the proprietary castable but not in the homebrew you make up yourself.
2. The homebrew casting should be de-moulded after a couple of days, any voids filled and then damp cured for a week. Extended damp curing is not required for castable refractory because it uses a different cement with a different chemical reaction that achieves very early full strength.

[kebwi]

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!