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Post by zelige on Dec 14, 2015 15:08:51 GMT
Hello All from Lancashire ! Great forum and inspiring builds! Have built a number of cob ovens here and there over the last few years and now attempting to go brick using reclaimed Accrington NORI reds. Can anyone give me some advice on my dome: -  Sort of making it up as I go along ... the dome should be 45cm high but hearth can only be about 77cm max diameter. Have worked out that if I lay an initial firebrick shiner wall with a stretcher row of red bricks above (see the two bricks in this arrangement to the LHS of the arch) that takes me to the correct height to build a 45cm dome - the stick in the picture being 45cm long. The brick dome won't be a full 180 degree hemisphere, rather a fraction of one - say 150 degrees. My concern is that the dome will exert lateral forces pushing out on the stretcher/shiner vertical walls. Am i right here or worrying unnecessarily? All feedback gratefully received. Should I dry lay the vertical wall? Was thinking of tying the stretcher/shiner wall together with external ring of chicken wire anchored with steel uprights into the 10cm vermiculite insulation below the firebricks and then cementing this to consolidate strength. Look forward to your responses! |
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Post by chas on Dec 15, 2015 13:01:14 GMT
Hi Zelige and welcome! I think I understand your concern about the lateral thrust - that said, big commercial ovens can be pretty 'flat': see ukwoodfiredovenforum.proboards.com/thread/1994/building-pizza-oven-italian-styleand links there. Couldn't you omit the stretcher course, spring the dome from your 'shiners' and get more dome height that way. I think a combination of the NY 'poured cement' method of knitting the bricks - not very carefully shaped, you'll notice - into a solid cap of brickwork, plus a bit more dome from the lower start and you'll be ok. It should just sit there... A chicken wire belt in that location shouldn't add to your problems (expansion/contraction) so can't do any harm. Have never considered dry laying the initial ring of brickwork - is there any advantage you've been told about or observed? Keep us posted! Chas |
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Post by zelige on Dec 15, 2015 14:59:47 GMT
Thanks Chas, yes that NY dome is very flat! Most of the height of those ovens must be insulation.
Ok, will get building. Will install chicken wire wrap around first row and pour over complete dome.
Could the cement poured over the dome be a runny version of the homebrew recipe or is it another mix?
Is the any risk in covering the completed dome in chicken wire to hold it together?
Many thanks, Z
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Post by chas on Dec 16, 2015 8:48:14 GMT
... Could the cement poured over the dome be a runny version of the homebrew recipe or is it another mix? Is the any risk in covering the completed dome in chicken wire to hold it together? The mix they used was a 'bag mix' and, I'd guess, capable of taking extreme heat - maybe Kilnlinings or Celtic would have a suggestion. It's an interesting technique, obviously successful and I've been waiting for someone to have a go at it! With the evident gapping between bricks filled with the mix you'll have in effect, a cement dome with scattered bricks... nothing wrong with that as long as the cement is the right sort. I don't think there's any great risk with adding chicken wire over the dome, but it won't stop cracking and as it's not normally used, why bother? Chas |
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Post by zelige on Dec 16, 2015 17:38:44 GMT
I will do the pour and see if I can film it. It looks a neat way of consolidating brickwork and adding thermal mass. Am guessing the homebrew would work as it's meant to withstand high temps but will have a word with Kilnlinings.
By the way, instead of a hemisphere I've been wondering if a parabola would resolve my original concern...
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Post by oblertone on Dec 17, 2015 13:14:59 GMT
I think the issue with a parabolic dome would be where do you put the fire whilst cooking ? Most WFO's use live fire while cooking a pizza; to keep it burning you need air in, and out. Tucking that fire under the reduced height of a parabola would ( I think) effectively dampen it. Then you have to consider side-thrust, which would be greater in a parabolic dome than a hemisphere.
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Post by chas on Dec 19, 2015 9:44:31 GMT
I will do the pour and see if I can film it. It looks a neat way of consolidating brickwork and adding thermal mass. Am guessing the homebrew would work as it's meant to withstand high temps but will have a word with Kilnlinings. By the way, instead of a hemisphere I've been wondering if a parabola would resolve my original concern... As per Oblertone, thrust may be an issue unless you create a structure that is so rigid, so stable, it could stand on 3 eggcups because the 'thrust' is entirely vertical. The conventional 'high-rise' hemisphere dome effectively converts the thrust smoothly to vertical so there's little inclination to spread. Brick window and door arches can be of a very shallow rise because the mass of brickwork each side restrains them. It's the restraint that stops them spreading, not the arching. Sorry if you know all this - it might be useful to others. Creating a shape for your dome that keeps its integrity and will just sit on your starter brickwork is possible and an interesting challenge. Do your research on a suitable 'knitting' cement medium and, like the NY commercial pizza ovens, I think you'll be ok. Unlike the guy in the NY build maybe wear rubber gloves? Best of luck, Chas |
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Post by zelige on Dec 19, 2015 11:36:57 GMT
Thanks both, wasn't aware of those differences btw parabola and hemisphere - very helpful and I'll stick with hemisphere.
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Post by cobblerdave on Dec 19, 2015 13:23:28 GMT
G'day
Your not building a full size building here.
You are building a dome one of the strongest structures on the planet.
But seriously a pretty small one.
Yes we are all home handy man. And of course we do go overboard from time to time.
Forget the chicken wire it's going to heat up and crack you mortar.
Of course the mortar going to fill those big gapes in the outside. As it expands and contracts it might crack.
My ovens 5 years old built on a soldier course hasn't expanded into destruction yet. No chicken wire or anything else.
Regards dave
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Post by albacore on Dec 19, 2015 21:09:16 GMT
I suspect that the Italian infill technique may just be a slurry of high alumina cement, though homebrew mixes may also work - there's a bit about the technique on this page towards the bottom. |
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Post by chas on Dec 20, 2015 10:40:54 GMT
I suspect that the Italian infill technique may just be a slurry of high alumina cement, though homebrew mixes may also work - there's a bit about the technique on this page towards the bottom. great link, and yes, post12 onwards. But beware... they're probably talking about conventional arches. With a flattened structure, collapse is the enemy. Go the Italian way, get that slurry well worked in among the bricks with every gap filled to the brim. Chas |
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Post by cobblerdave on Dec 20, 2015 12:32:50 GMT
Gday
Worse thing about building to a form. Till you pull the form out you never know what it's going to look like.
Like I said 5 years cooking now, I'm long over caring
Regards dave
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