Steel Dome Oven

[Wiley]

Re: Steel Dome Oven

Hi Firebug,
OK, first thoughts and assumptions on your query:

It would appear you are considering using no other heat retaining medium other than the steel plate bent to form the barrel vault for the ceiling. Without knowing the exact shape you are envisioning it would be hard to get an precise weight. However, steel weighs about 40.8 lbs per sq ft one inch thick (board ft). So a flat sheet 4' x6' and 1/2 inch thick would weigh about 490 lbs and in the interest of getting some sort of figure with which to work (ball park figures) doubling that for the curve of the ceiling and the ends etc would give us a figure under 1000 lbs. My gut feel is that that is too little a heat reservoir/ heat sink for that large a volume. I suspect it would heat up fairly quickly but also cool down quickly as well. We don't get something for nothing. BTUs need to be liberated; the heat transferred into the heat sink then released back. It's the released back that we are using to bake with in addition to the heat from a ongoing fire to maintain a certain searing/reflection/direct radiation in the case of baking a pizza. I am not a thermodynamics engineer so alot of what I am saying and thinking is "gut feel" (and we all know how much that "gut feel" can get us into trouble). But if one knew the heat capacity of steel and compared it to the heat capacity of firebrick/stone/clay/terracotta one might be able to produce a better answer as to "Would this work?" And by "heat capacity" I mean how much heat (BTUs) can this material soak up/contain/hold? and how fast does the material cool down, give up that stored heat?

So, I suspect such an oven would heat up very fast and but that controlling the heat might prove problematic.

I'm sorry that is not much of an answer. I used the steel dome of my oven as an uncrackable, unspallable, hard to damage and smooth interior form to support the heat reservoir, not as a heat sink itself. I suspect that my steel interior more quickly distributes heat to a larger surface area of the heat reservoir than straight bricks do, however, that is once again, "gut feel" and I have no hard evidence to support that supposition. I do have evidence that a steel dome doesn't crack, that in advertantly striking the interior with a peel results in minimal (read that as no) damage.

Hope this helps,
Wiley

[firebug]

Re: Steel Dome Oven

Hey wiley,

I'm new to this thread and you have answered many of my questions, I plan on building a trailer mounted wfo,my plan is to build metal base welded to trailer, them form up base with cement and perilite then one layer firebricks for the floor, take 1/2 steel bent for a big barrel vault 4x6'.build a dog house around it fill it with 6'' or more of perilite,I want to do a hearth in the front,,,,all done with fire rated materials I want few moving parts I think this could work ,what are your thoughts?

[christo]

Re: Steel Dome Oven

Good to talk to you. I've been away too long!!!

The stuff I used has some sand in it - more like a smooth stucco finish. I'm not sure if they have a smoother finish.

I'm hating I sold my boat - but not so much....

I'm heading down to FL soon to do some sailing and fishing with some old friends (who still have their boats!!)

Please send some pics of the pavillion - sounds very cool.

Take care,

Christo

[Wiley]

Re: Steel Dome Oven

Christo, Actually I haven't gone any further with that problem. We've been busy....

I've been getting ready to haul my boat. We're hauling out tomorrow and hopefully we will only be out a week. Lots of lost time what with weekly parent visit and grandkid's birthday on the weekend so it might be longer. That's of course assuming we don't find any major problem(s). But we took her to the dock today and off loaded extra diesel and water and sails and such like, both my wife and I agreed we need to spend more time on the water. We want to work my/our schedule so we get more time on the boat. Priorities!

I also cleaned the mooring chain last week and decided I want to replace it before winter. So once we are back in the water I will be replacing the top pennant of her mooring (20 ft of 1/2 inch chain) and probably add an additional 3 to 4 ft of the heavy chain (1 1/2 inch / 9+ lbs per link stuff) so I don't have to make these swaps at low low tide.

But soon as that's done I plan on finishing up the pavilion and finding some sort of elastomeric paint, how thick (viscosity not film thickness) is the Dryvit material? I looked at some hypalon paint, which I know is tough and which will accept an overcoat of the paint I have. A bit on the pricey side though.

Bests,
Wiley

[christo]

Re: Steel Dome Oven

Hey Wiley -

How are you coming on the paint? I used some smooth Stucco-type finish from Dryvit that remains flexible. So far so good. There was one area on the foundation that had a hairline crack and I have not seen it since I coated it.

The color seems to be holding it's own.

Good luck.

[Wiley]

Re: Steel Dome Oven

This past few days we in the Pacific Northwest have been experiencing unusually hot weather for us with temperatures in excess of 100 F. This morning while passing my WFO I noticed a hairline crack which I can I think attribute to this hot weather. It is only on the southern facing exposure so although I have been using my WFO a fair amount these past few weeks, I'm assuming the sun exposure caused the crack.

I'm going to start looking into some sort of elastomeric paint which I think might "fix" this issue. The concern, of course, is water intrusion during our wet winters. Has anybody used or have a brand etc. that they can recommend?

Thanks,
Wiley

[ClintonJ]

Re: Steel Dome Oven

Thanks Wiley,
The last thing I want is to build something that would eventually crack and have to be taken apart and repaired. I'm working on finding and buying a condemned propane tank so that I can get started on the oven this summer. I definately think that your oven is the best idea for someone like me with limited masonry skills but access to a friend with a welding shop. I'll post some pictures when I get started.

[randall4483]

Re: Steel Dome Oven

Wiley, I knew you would have a good reason?

dmun, did you build a steel dome oven also? If so, do you have any pictures or posts?

Thanks guys,
Randall

[Wiley]

Re: Steel Dome Oven

Randall,
There are a couple of reasons I decided to go ahead and move from "design mode" to "build mode" a year ago. I was gathering pieces and everything seemed to say: Here's what you have and the proportions are so very close to design perfect that if you don't give it a try, well you're less than you thought you were (there's a nasty (at times) task master who shares my head with the lazy-lay-about who I really am).

So:

The hemisphere I used had a nominal diameter of 40 inches. Since the half I had was cut with the backing ring it had a bit more of interior dome height (otherwise would be radius). The radius of the split rim, which I used for the entrance, was such that if I lessened the interior height of my dome by the thickness of one fire brick, the ratio between the height of the entrance and the interior height of the dome was very close to the "sweet spot" of 63 %.

So lots of things fell into place: I wanted to keep the integrity of the base of the dome (the backing ring) to minimize possible distortion due to heating. The interor brick allowed that. I liked the look of the arch...a rainbow, a half circle. This allowed me to use the split rim simply cut in half. Otherwise I would have added pieces to the bottom of each side to increase the height of the entrance; or cut them down as needed.

I was unsure of the long term effect of the bottom edge of the dome expanding and contracting and so moving across the relatively soft vermicrete. By setting the dome on a "split" I increased the hardness of the supporting material and lessened the likelihood of problems with the steel dome slowly over the years working/wearing its way down and consequently out of direct contact with the refractory (basalt Fondu concrete). By setting the dome on the split and needing the interior full thickness brick I increased the thermal mass of the hearth. This I had some doubts about but has worked out OK; time from "match to pizza heat" is about 40 minutes; fine enough for me.

So that's "the why?" of the interior brick hearth.

Bests,
Wiley

[dmun]

Re: Steel Dome Oven

Why the cutting and shaping the hearth bricks that fit inside. Could I not just set the dome on top of the fire bricks and save the effort of cutting and shaping. I'm sure there is a reason!

The reason for having your floor fit inside the dome is that in commercial ovens subject to daily use, the floor may need to be replaced every decade or so. I see no reason to use that method for once-a-week use home ovens. I built mine on top of the brick floor with almost no cutting.

[randall4483]

Re: Steel Dome Oven

Update wth photos....

I got to spend "The Fourth" cutting and shaping the hearth bricks which fit inside my steel dome. All went well although I had brick dust everywhere :-(

But today I got to power wire bush my dome and then set it on top of the stand. Inspite of working alone, all went very well. :-)

Wiley

Why the cutting and shaping the hearth bricks that fit inside. Could I not just set the dome on top of the fire bricks and save the effort of cutting and shaping. I'm sure there is a reason! Thanks, Randall

[dmun]

Re: Steel Dome Oven

Several makers have reported that the cast refractory - SS needle combo is hard to work with. There have been more vent transitions made with the stuff than full domes. I have no personal experience with refractory concrete.

Our Australian builders have more experience with castable: for some reason firebricks are ruinously expensive "down under".

[Wiley]

Re: Steel Dome Oven

ClintonJ,
Thank You for the kind words. However regarding your questions I would suggest you search out Ed Schmidt or David S both of which built WFOs from castable refractory. Ed Schmidt's was constructed of pieces and assembled and David S (he uses lower case: david s) WFO is a single piece casting.

The material I used was "Fondu" (calcium aluminate cement) and crushed basalt and so far has worked well for the purpose I intended. I'm not as certain how well it would perform if it was in direct contact with flame. One of the benefits of using a steel dome in my construction is to protect my homemade cast refractory from direct contact with flames. With a wood fired oven it is possible to get localized temperatures in excess of the rated temperature of the cement and that cannot add to the durability of the WFO.

Regarding cracking, I suspect that larger WFOs might be more successfully constructed using cast sections rather than as a single piece. I think that perhaps the biggest concern with a single piece oven is how to accommodate the stresses created by uneven heating. Multiple sections would allow differential expansion due to uneven heat and thus not be as susceptible to cracking. Dmun's geodesic dome might be a good place to start if one was thinking along the lines of casting larger pieces that would fit together in a repeatable pattern thus minimizing the number of sectional molds

I'm not familiar with the "large fiberglass sand filter body" which you are suggesting to use for a plug mold. Do you have a link?

Sorry I couldn't be of more help. There are several people who have built cast ovens on the Forum who are far more qualified to address your questions than I am.

Bests,
Wiley

[ClintonJ]

Re: Steel Dome Oven

Hello Wiley- I'm new to the forum, but have been reading your thread and referring back to it often as I plan on building my own oven. I've been back and forth deciding on exactly how to build it. My first idea was just to build it exactly like the pompeii plans, but then I started reading about your project and was very impressed with the outcome. You seem to really know your stuff when it comes to insulation, refractory material, etc... My latest idea is to use a large fiberglass sand filter body (40") as a mold for cement refractory material. Basically cover the cut fiberglass dome with aluminum foil and pack the cement around it to a depth of 4", possibly including some wire mesh inside the cement for strength, allow the cement to cure and (with lots of help) remove the mold and set the cement dome in place. I would appreciate your opinion on this idea. My worries/questions are:
#1 - What type of cement/aggregate to use?
#2 - Should I use some type of wire mesh to strengthen the dome?
#3 - Will whichever type of cement I use eventually break or crack?

The rest of my plans are pretty basic. I'll Cover the dome with ceramic blanket and perlite or vermiculite, add a vent and hearth, all of this on a insulated base topped with firebrick (per pompeii plans). I've searched the forum and googled "castable pizza oven" and haven't gotten any reliable results. Any input would be greatly appreciated.

[Wiley]

Re: Steel Dome Oven

Randall,
I think the thickness I would choose would in part depend upon how good the join is between the mating pieces. I'm guessing you are speaking here of the piece I used between the dome assembly and the outer entrance ring. If it is a close fit the thicker stuff may not fit, if loose then the thicker would fill the extra space (sort of have to look and make your best guess). I don't think there is a magic number with this. The major idea is to stop the expansion and contraction of the inner dome from causing problems with the outer shell/exterior of the WFO thru the slip surface. The retardation of heat transfer from dome to rim is less controllable as the space for such insulation is small.

As for thermometers I have been using a Harbor Freight infrared thermometer, a cheapie (when on sale $29.00) and so far have been pleased. I did not opt for thermocouples in the floor or dome. In fact we are planning a trip to Italy this fall and I bought a second HF infrared thermometer to take along. Figuring there was a possibility of it being confiscated by our well meaning (but basically idiotic) homeland security people either exiting or entering our country. And if not then perhaps I can give it as a gift in Italy to a helpful pizzaiolo. The units work well enough and are cheap enough to be considered expendable. I'm most curious to get some real time data on temps in their ovens.

Hope this is helpful,
Wiley