steel liner question

[La Boulangere]

Hello everyone! We've been badly let down by our 'builder', so the cement is crumbling between the bricks on our dome and the builder left very big gaps between the bricks too (despite them being shaped for the purpose). Ours is a shallow dome, for breads & pizzas hopefully. Space is too small to crawl in and fix the problem, so we want to line it with stainless steel - hopefully avoiding the concrete crumb pizza topping. Does anyone know how thick the steel should be, how much it will warp or buckle over time and at temperatures of 450 C? We are thinking of welding steel ribs to minimise buckle, but not sure what gap to leave between the steel liner and the bricks. Please help - we're getting very down about this Thanks in advance!

[david s]

Re: steel liner question

Hello everyone! We've been badly let down by our 'builder', so the cement is crumbling between the bricks on our dome and the builder left very big gaps between the bricks too (despite them being shaped for the purpose). Ours is a shallow dome, for breads & pizzas hopefully. Space is too small to crawl in and fix the problem, so we want to line it with stainless steel - hopefully avoiding the concrete crumb pizza topping. Does anyone know how thick the steel should be, how much it will warp or buckle over time and at temperatures of 450 C? We are thinking of welding steel ribs to minimise buckle, but not sure what gap to leave between the steel liner and the bricks. Please help - we're getting very down about this Thanks in advance!

I think you're in unchartered territory. Stainless is notorious for warping and the thinner it is the greater the tendency. I assume your oven is a barrel vault because a dome would be extremelly difficult to line given the compound curve.

[Laurentius]

Re: steel liner question

Add photos, please.

[Wiley]

Re: steel liner question

As an owner/builder with a steel lined WFO I concur with everything stated in the replies so far. IMHO A steel lined WFO is a very viable way to go and I would suggest it to someone building an oven. However, as a repair technique for a failing WFO I would not advise taking that route. There needs to be intimate contact between the liner and the refractory heat sink/heat reservoir for efficient heat transfer between them. This is not difficult to achieve when building, but as a retrofit or repair I can see it as very hard to assure.

Like Wotavidone, I would also advise carefully deconstructing your WFO and rebuilding.

Bests,
Wiley

[nissanneill]

Re: steel liner question

La Boulangere
Thee is only one way to overcome this problem.
Knock it down carefully, without damaging the bricks, and rebuilding it.
Should you want a steel lined oven, and as Davis assumes that you have a vault oven, get a sheet metal worker to bend you up a 3mm steel liner and even you can then easily lay the bricks to sit on this liner which doubles as your formwork. Just put a thin mortar coat to bed the bricks up against the liner so that no air gaps will be present as the air acts as an insulator.
Could you have don as bad a job as your "builder"? I built my 40" pompeii in 2 days so it will not prove to be a too difficult a job to rebuild, and you will end up with a much better job.

Neill

[lovibond69]

Re: steel liner question

Hello Wiley,
I have both, a stainless 55 gallon barrel and a 15 gallon keg I was considering using one of them to line (build over) my wfo. My thought is to cut the barrel length direction (top to bottom) and lay it flat to create a barrel dome. Then cover with perlite/concrete insulation and possibly some fire blanket - then brick the top for the finish as I have 200 red bricks laying around. The floor would have fire brick with insulated perlite/concrete form poured under that.
Does this sound workable?
I was hoping to use the 15 gallon keg option for a small oven. 14" wide by 23" long by 15" high (inside dimensions). I like the smaller keg because the front and back "walls" if you will, are curved to create a smooth transition to the ceiling. The larger 55 gallon drum has 90 degree wall angles.
With a very small oven like this - I'm not sure that the curved aspect would matter much...but this is all speculation in my part.
Any thoughts and suggestions?

[Wiley]

Re: steel liner question

lovibond69,
Sounds workable but you will need to have some sort of refractory heat sink/reservoir outside the stainless keg half. You should be able to easily figure the space available between the outside of the half keg and the inside of the half 55 gallon drum before doing any cutting. As the WFO will be small you probably won't be looking at 4 inches of refractory but I would think 2 to 3 inches would heat up fairly fast, yet be sufficient to bake pizzas. Whether the remaining space (outside the refractory but inside the drum) is sufficient for insulation is another matter. Perhaps using a kaowool type ceramic insulation around the widest part of the keg might be worth considering to keep the outside of the WFO from getting too hot.

Hope this helps,
Wiley

[lovibond69]

Re: steel liner question

Hi Wiley,
Thanks for the reply! You pose an interesting view which I had not considered. Your idea (tell me if I read this wrong) is to cut both kegs and place the smaller one inside the other. The space in-between would be filled with a heat sink refractory and above that would lay the insulation layer and above that, the larger barrel...is that correct? Sounds like a very good idea.

My thought (and main question) was to use either of these kegs - one or the other....and if going this way, which one should I use to get the best efficiency based on internal size? I would only be cooking a couple of pizza's once or twice a week and would like it to be able to reach the 700 - 900 degree mark that is typical of the brick domes.
Do you think it would perform as well?

I assume by your response that when using either liner alone, I could still cover the barrel dome shape with a dense refractory - 3:1:1:1 sand:fire clayortland:lime mix?
Then cover that layer with ceramic cloth and place a "finish" coat of percrete - 5:1 perliteortland insulation layer on the outer-most section?

Thanks again!

[lovibond69]

Re: steel liner question

Here is what I have so far.
4" layer deck of perlcrete on top of rebar/contrete form. I cantilevered the large double angle iron to support the granite shelf to the left side.

I have plenty of full fire bricks to form the base (floor) of the oven. Now to choose what type of oven to build!

[Wiley]

Re: steel liner question

Lovibond,

Yes, that was my assumption: cutting both and placing one inside the other with refractory and insulation between the two. My bad if I got that wrong. It has been done successfully, (see: http://www.dentedbuoy.com/ and ? History of the Buoy oven). Having enough space between the two shells to have both the refractory and the insulation is the issue. Dented Bouy's WFO has an interior done of 48 inches diameter and a 60 inch diameter exterior dome. Plenty of space for refractory and for insulation. The two shells you have may not be so accommodating.

Regardless, using either with a refractory and insulation and exterior shell of whatever (stucco, framed small building, etc) will most likely work well. There has been one WFO made by a member of this forum with formed stainless steel sections welded together to form the interior dome. Very cool and I am envious of that owner/builder's skill.

Which of the two shells you decide to use (that is if the measurements preclude using one within the other) something to keep in mind is the height of door to interior ceiling proportion of 63%. Vary much from that and most likely the WFO will not draw well or have good interior gas flow. That 63% ratio controls the final height of the door. My WFO can accommodate a fairly large turkey in a roaster (although I had to modify the handle on the top of the lid to fit the height). To me the larger of the two would be desirable as it would permit a higher door height thus larger pots, roasters etc.

There was a WFO built here that used a half whiskey barrel for a form and which was burned out with the initial firing so having a shape cornered aft wall joining the rounded ceiling seems to work...or at least did in his case. There has been a lot of WFOs built with a barrel roof and a flat aft wall as well. Check archives: http://www.fornobravo.com/forum/f3/i...ioni-4420.html.

As for the actual mix of the refractory, IMHO lots of stuff can work, I have seen where some use crushed firebrick and portland cement and lime mix. Personally I like the calcium aluminate (Fundu) as it is high temp and goes off quite fast...I don't suggest adding lime as it really speeds it up.

Hope this helps,
Wiley

[lovibond69]

Re: steel liner question

Yes, it does help - very much. Thank you Wiley!
I really like your idea and will think about the doubled stainless liner/outer shell concept. I will take some measurements looking at the possible door opening and see what that may look like. My gut is telling me that the smaller liner may be too small as far as the opening is concerned but I will look into it.
Thanks again - I really appreciate the encouragement and interesting view point.

pics: Back yard fire pit - now for my oven...

[lovibond69]

Re: steel liner question

OK, I just looked at the 15.5 gallon keg. If I were to raise the cut dome up buy placing fire brick under the bottom walls of the the liner - raising it 4.25", I will have a floor to ceiling height of 14.25". With the 63% door opening rule - I came up with ~ a 9" (8.9775") high door opening (9" x 14"). The total interior will be 25" x 14" not including a domed door opening made of fire brick.
When I cut the stainless liner I can also cut out tabs at the base that can be bent to form over a few bricks to help hold it all in-place.
How does all this sound in terms of size of interior, door opening or anything else I haven't thought of?

[Wiley]

Re: steel liner question

Lovibond,
To me having the width of the entrance the same as width of the interior will be unusual. That is not saying it wouldn't work just that I have no experience with a WFO so constructed. Most of the WFOs that I have seen that were built using standard 55 gallon drums have the entrance a bit smaller than the whole width.

There are some compromises that will have to be made: The fire will most probably have to be at the back of the oven. So managing the actual cooking will require close attention...most of us place the fire to one side so we can observe the cooking where the pizza is closest to the fire.

Since the interior of the WFO you are suggesting will be a lot smaller, the luxury of being able to move the pizza to accommodate heat/cooking rates will not exist. Most of us have an areas of the interior of our ovens which are different temperatures so one can move the pizza to adjust rates of cooking.

For a quick one at a time WFO pizza oven I think the concept it will most likely work and probably better than some. At least I would expect it would produce a pizza that looks like wood fired pizza should look. Not like some thing that came out of a toaster oven. IMHO what a WFO pizza should not look like: Green Rocket Oven -

Bests,
Wiley

[lovibond69]

Re: steel liner question

Great, thanks Wiley,
I can cut the door opening arch making the lowest part 13", leaving a 1/2" on either side of the door... I know, not much, but it may help with the stability having a 90 degree angle at the base in the front. (I just bought a 12" peel so I cant go any smaller - lol)

I may even be able to squeeze (pull) a 15" or 16" width out of the entire base by bending the base wall curve straight (with relief cuts at each corner I imagine) - this would then leave a ~ 1.5" wall on either side of the door opening, at the base.

I just purchased 2 boxes of ceramic blanket - 8#, 24" x 25' rolls and was able to source fire clay, 2 bags (50lbs each) for $22.00.
For the refractory mix - does the type of sand really matter that much - its all pretty much silica anyway....isn't it?

I plan on making my own dense refractory and slapping on a 3" coat over the dome for a heat sink. Many have mentioned to add some type of rope fiber, etc so when that burns away, it leaves a capillary structure for steam to find an escape. If this is the theory - wouldn't it be possible to throw in a cup full of perlite into the mix to allow for similar air pockets/steam egress? I would think at this volume, the perlite would not detract from strength or take away from the heat sink property via insulating the material, with using so little....?

I'm still thinking of your suggestion to use the 55 gallon barrel over the 15 gallon barrel - with the dense refractory, ceramic fiber and perlcrete layers in-between. The outer barrel would protect everything from rain and snow. I was considering slicing a 1" section (length of the barrel) on top to form a ridge vent of sorts to allow moisture to escape, mainly. It would be covered with a 3" or 4" length of curved stainless cut from the waist side of the barrel.

With this ridge vent cut in the top of the outer barrel I could pour in dry perlite over the ceramic blanket to fill the entire remaining space and then cover with the ridge plate? Sound viable?

Is it a good idea to use more insulation under the fire brick or will the 4" perlcrete layer insulate well enough?

Sorry, so many questions....
Thanks again!

[Wiley]

Re: steel liner question

Lovibond,

I like the idea of going slightly narrower (13 inches). That curve at the front corners will add a lot in the way of stiffening the front corners.

I wouldn't try to widen the keg (if I'm understanding what you are suggesting). Stainless has a great propensity to work harden..first bend is fairly easy but after it bends it can increase it's resistance to bending in that spot by as much as 100%. That is why it is hard to straighten...bend a piece 90 degrees and then try to bend it back to straight. It will bend elsewhere making for a "s" shape in cross section. The keg already has shape (thus was work hardened) from when it was formed, personally I would limit my tinkering with it's shape by bending. Note that some alloys are more problematic in this respect than others.

Sand is not all the same. Depending upon where it comes from it can be mostly calcium carbonate (coral and shells or limestone) or can be all volcanic or any of a mix. I would look into finding an inexpensive source for blasting sand or if you were fortunate enough to live near a foundry see if they have spent green sand (which is olivine). You want the volcanic sands... usually dark heavy sands (although silica sand can be white colored) or artificial sand such as blasting media.

I do not understand why someone would want to intentionally add something like rope fibers to the refractory...you want it as dense and solid as possible. If I use the logic test of running something to extremes... would you want a solid chuck of basalt or a frothy piece of pumice? Adding the fibers in order to have them burn out and leave steam passageways seems like an exchange of a little saving in curing time for a poorer quality heat sink in the finished product IMHO.

Having a vent is a good idea. I don't know if you need as big a vent as you suggest. In my WFO I left a space around the chimney so it was both high and able to easily be shielded from water intrusion (rain etc).

Pouring loose perlite over the ceramic fiber is similar to what I did when I built my WFO only I used vermiculite. Personally I fine perlite more irritating to my skin so prefer working with vermiculite.

4 inches of perlite cement concrete underneath should be more than enough. This will be a small WFO and I don't think long term holding of heat (overnight for example) for a second day bake will be its long suit.

Hope this helps,
Wiley