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Post by chas on Sept 16, 2014 16:48:23 GMT
Ok, time to start after 4 years of dithering...Following forum tradition, I'll post progress reports on my build, which is going to be a clay-and-old-soft-redbrick dome behind a brick facade with chimney (yet to be fully thought through) and a reclaim oven door set in there somehow. I think it's a 'Pompeii' - if it's not, mods please move. It'll sit on a 4' x 4' platform of concrete slabs on a brick and concrete lintel base. I had intended to cover the slabs with pamments bedded in lime mortar and build off that, but following info gained here I revised the floor to isolate/insulate/create more mass for the hearth. So now it's pamments in lime mortar within a ring of bricks on edge (leaves awkward naked corners of slabs showing, but I'll sort that somehow) with about 2.5" of vermicrete fill A late refinement was the offer of a brick saw which allowed me to 'wedge' the brick ring, reducing the joint size. At least half of the bricks will be covered by the dome and what's left may well end up under a detail finishing ring of some sort, so maybe only the vertical joints will show - but instead of an inch+ they are more conventionally brick joint size. So, the basic layout of the first phase - with the original whole bricks:  the revised one with the cut bricks and a circular template to build to, also used to cut pamments and keep starter courses regular later:  Day 1: ring laid, entrance laid, vermicrete layer packed in:  day 2: pamments cut to shape and bedded, the groove is to take the lower flange of the doorframe and keep it secure:  the doorway, starting the main bodge, hoping a chimney will emerge:  |
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Post by chas on Sept 24, 2014 13:52:14 GMT
Was hoping for an afternoon at dome-raising - but it's chucking it down... this is by way of an update, discoveries on the way and a reflection on what might have been done differently. I'll get a pic in the morning to bring us up to speed:
I got two courses of half-bricks set in lime mortar around the floor - and realised by how in progressing the doorway, I'd not provided any sort of bond between it and the dome behind. Even when I get four courses up I'll just have a joint butted up to the 9" work on the front, but after that I'll try to work some sort of bond into the join. I think I can rely on the joint to stay intact for cooking purposes, but having gingerly opened the door, realise too late what a considerable weight hangs out the front from the frame, and I'm a tad concerned it may just pull at the brickwork...
The mixing of clay and sharp sand 50/50 by trampling on it in a mortar mat worked surprisingly well - put some sand in, then spread clay over it and added rest of sand on top. It mixed easily, needed a bit of trowel work to bring it to the middle from time to time, but was easier and quicker than I feared. Next batch I will a) have an easier pair of boots to slip off b) have somewhere clean to step out onto c) have another pair of slip-ons ready. You don't want soles clarted in clay and rubbish when starting another batch, so you really want to leave the boots back at the mat when you wander off with the clay mix. Remember to put the boots in the shed in case it rains...
The clay is red earthenware potters clay. I got about three buckets of it some time ago (it doesn't go off) free from a potter who had mistakenly allowed a batch to get too soft for throwing.
The trammel has a forked 'tail' to rest on a centre screw set in bricks (the 63% rule gives two courses before dome, and dome is the radius of the floor. Have already decided I'll need to cut the fork back a bit as work progresses or it will be standing up too high.
Cutting a selection of bricks is more boring than laying them, but it has to be done. The wastage is considerable, but I remember smaller bits become more useful higher up.
A paintbrush dipped in water is good for neatening the joints once excess is scraped off. A fingertip is useful too...
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Post by chas on Sept 25, 2014 16:40:57 GMT
Ok... so here's the first couple of courses - half bricks in clay:  I got on today and reached the top of the brickwork surround - decision time re a chimney or not. Decided a) it should have one b) I just couldn't get my head around how we achieved it on the test build (I have now - it used bricks on edge to create a flue within 9" work) and cast around for another solution to be got from stock. Found this old bit of 3" clay pipe, shaped it to fit the ramp, cut the smallest hole I could with the anglegrinder to present a smokehole to the inside of the dome. Hopefully:  and wedged it in place with the last of the first bucket of clay:  A bit of post-rationalisation: had always intended to have the chimney at the front, but was bothered that it was sited there to be used by pushing a 'door' forwards or backwards into the entrance to regulate smoke clearance. I don't have that now that I've got the iron door - so why have the chimney at the front where I am? Anyway, I think it must simplify the build, and I can turn my full attention to getting the union between dome and front right without the complication of a flue. |
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jms
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Post by jms on Sept 27, 2014 14:49:15 GMT
Having the chimney at the front means hot air flows out at the ceiling and then new air is drawn in at the floor, which not only assists with oxygen getting to the fire, but the hot air gets pulled over the top of the pizzas for cooking toppings. During firing the door will have to be fully open for oxygen anyway.
The opening on the pipe is tiny compared to the area of a normal chimney vent, so I'd bet that you end up getting most of the smoke coming out of the door anyway simply because it is the path of least resistance. Lots of ovens can get away without having a chimney at all, but the trade off is a full vent at the front keeps the smoke out of your face and away from ground level during wind.
I don't think the pipe would help very much, so you may want to consider taking it off and doing a chimney-less build or building a full chimney vent.
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Post by chas on Oct 1, 2014 9:48:47 GMT
Having the chimney at the front means hot air flows out at the ceiling and then new air is drawn in at the floor, which not only assists with oxygen getting to the fire, but the hot air gets pulled over the top of the pizzas for cooking toppings. During firing the door will have to be fully open for oxygen anyway. The opening on the pipe is tiny compared to the area of a normal chimney vent, so I'd bet that you end up getting most of the smoke coming out of the door anyway simply because it is the path of least resistance. Lots of ovens can get away without having a chimney at all, but the trade off is a full vent at the front keeps the smoke out of your face and away from ground level during wind. I don't think the pipe would help very much, so you may want to consider taking it off and doing a chimney-less build or building a full chimney vent. Useful thoughts jms... provokes a couple or three questions: I was under the impression that the 'front-flue' design was like that cos it was easier to incorporate a flue in the brickwork rather than the dome, and that in operation (bear in mind I've never actually used one) the push-fit 'door' sometimes used was left out until the smoke phase had finished, then pushed in past the flue opening to seal the oven in cooking mode - but you're saying you don't cook in a sealed oven, you want hot air passing through? Doesn't that mean some heat's escaping? You're right, the smoke hole in the pipe is small - to be contained within the dome it needed to be - and maybe I could have hung the pipe over the inside line of the dome a bit to get some smoke up it that way as well as through the hole (still could - it's only held in place by the clay). Wouldn't the same "hot air flows out at the ceiling and then new air is drawn in at the floor" result as if the chimney was at the front? Either way, the flue entrance will not be at the ceiling height if by that you mean the top of the dome - it's down nearer to top-of-door height - is that wrong? In use, I was expecting to fire-up through the smokey phase with door and flue open, then bung a loose-fit cap on the chimney and close the door to cook. You could maybe fast-track me through some pizza and focaccia f-ups if that isn't how it happens... Chas |
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jms
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Post by jms on Oct 1, 2014 16:26:32 GMT
Useful thoughts jms... provokes a couple or three questions: I was under the impression that the 'front-flue' design was like that cos it was easier to incorporate a flue in the brickwork rather than the dome, and that in operation (bear in mind I've never actually used one) the push-fit 'door' sometimes used was left out until the smoke phase had finished, then pushed in past the flue opening to seal the oven in cooking mode - but you're saying you don't cook in a sealed oven, you want hot air passing through? Doesn't that mean some heat's escaping? The flue goes on the front traditionally so you get an air flow pattern like this  The flue also doesn't go directly on the dome because that means that the flames/heat has an easy exit rather than being used to heat the structure. I used to have a rubbish clay oven which I built in a weekend, and the tiny chimney I formed on it was nearly at the top of the dome, and so the flames would come firing out the chimney which looked amazing but was pretty useless for fuel/heat efficiency. For cooking pizza the oven door is fully open. You keep a fire burning in one side of the oven, brush the floor on the other side, and then cook the pizzas from a combination of heat from the floor, ambient heat from the brickwork, and heat coming off of the active flames. For cooking things like bread or chicken what you do is perform a firing to get the brickwork saturated with heat, then you let the fire die out, clear the embers and stuff out, then wait until the oven gets down to the cooking temp you need. Then you block the entrance and use the ambient heat of the brickwork to cook just like you would in a kitchen oven. You're right, the smoke hole in the pipe is small - to be contained within the dome it needed to be - and maybe I could have hung the pipe over the inside line of the dome a bit to get some smoke up it that way as well as through the hole (still could - it's only held in place by the clay). Wouldn't the same "hot air flows out at the ceiling and then new air is drawn in at the floor" result as if the chimney was at the front? I've seen an oven on fornobravo forums where the chimney was at the very rear of the oven, but that oven was enormous, so the guy didn't have the problem of losing all the heat up the chimney. For a normal sized oven keeping the vent at the front is the best compromise between efficiency and ease of building. Either way, the flue entrance will not be at the ceiling height if by that you mean the top of the dome - it's down nearer to top-of-door height - is that wrong? In use, I was expecting to fire-up through the smokey phase with door and flue open, then bung a loose-fit cap on the chimney and close the door to cook. You could maybe fast-track me through some pizza and focaccia f-ups if that isn't how it happens... Chas A chimney vent could start below and in front of the dome, like in the picture above. This is how my oven entrance looks  The inner door has a lip prior to the chimney which means I can get a good seal by pushing my removable door against it. However I just looked again at your pictures and I can see the problem you have with space at the front of your oven, so I don't know what is the best option. I don't think the pipe chimney arrangement you have will be particularly useful, but I also don't know if you'd be able to fit a proper vent on the front. |
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Post by chas on Oct 1, 2014 17:43:58 GMT
Right-ho JMS - that's all I need to convince me!
Now I see what we're aiming for - and with a bit of brick-whittling I think I can revert to the front flue... the original design got one within the 9" brickwork by using a pair of keystone-shaped bricks on edge. I think I can get myself an extra half-brick depth to work in and do something similar.
Thanks for taking the time to explain all that.
Chas
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Post by chas on Oct 6, 2014 16:55:58 GMT
So, a few dry gaps in the weather coincided with my availability, and we've moved on apace... having decided to abandon the rear flue, I made a way of getting the extra half-brick depth needed to accommodate the flue (by way of a back-track, you can do this in 9" work with brick-on-edge keystones, but I scuppered that by using a recessed oven door leaving no space) Not pretty, but 1) it does oversail the dome, getting the bond I'd lost, and 2) by cutting the three central arch bricks to 3/4 length and backing with a shaped on-edge keystone to match, I get a flue:     Completed with pamment capping for a beer shelf:   A burst of clay and whittled bricks, and the dome was 'up and over' in no time at all, just minutes ahead of hours of rain....  Timely, as I won't be able to do much more for a couple of weeks, so it can all dry/set in the meantime covered and without the temptation of test firing. So, just need to finish the flue top and render the dome to add a bit of mass and waterproofing, and then it's experimental bakery time... Chas PS, only recently caught on that my small pics will open full size if you click on them - obviously haven't got to grips with Postimage! |
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Post by chas on Oct 23, 2014 15:04:04 GMT
Back from my work and travels (must have been close to Davey and his North Sea build going up the A9 - there can't be many places where you see rigs by the roadside) and managed to find an hour or so to complete the extra couple of courses, plus place a 6" sg socket I scored from Sutherland and brought back for the job... now to find a source of K-Rend and get the thing protected. I was surprised to find how soft the clay had remained, under cover as it was. Anyway, uncovered while the weather remained dry and with a couple of small test fires, it's setting/hardening/solidifying nicely now. Chas   |
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Post by chas on Oct 26, 2014 9:47:11 GMT
Found K-Rend and base-coat locally, and lashed a coat over the dome yesterday in lovely weather. White is very white, isn't it...  |
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jms
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Post by jms on Oct 27, 2014 0:31:53 GMT
No insulation layer?
I don't think I've ever seen K-rend put straight onto the dome before.
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Post by chas on Oct 27, 2014 9:49:11 GMT
No insulation layer? I don't think I've ever seen K-rend put straight onto the dome before. Back before I started the build, over in 'Insulation Tips', I was influenced by TonyB's post where he said "The key question wfo builders need to be clear about is what they intend to cook which should then drive the design." suggesting that 'flash-cooked' pizza and focaccia could be cooked in an uninsulated oven but conventional long cooking would require heat retention and thus insulation. Or mass, of course - a hundred years ago the insulation choices we have didn't exist, it would most likely have been sheer mass of brickwork. Going back a bit, I was lucky enough to get on an oven building course a few years ago, and the only 'finish' to the dome made of half-bricks stuck together with clay was a lime mortar render to protect the clay from damp. These were a 'Mk4' oven design and the product of experimentation by a bricklayer and brickmaker duo... I just assumed they worked. Taking all this together, and having discovered this place, in mine I made provision for an insulating layer - there's 3" of projecting brick ring at the base to build it up from - but I'm not sure I need it for the use I have in mind. And, of course, I'm anxious to get on and actually cook something in there! So, there's a base and topcoat of K-Rend over the dome to help keep it dry and we'll start some experimental firings. I'm expecting that if I can get it up to temperature, it'll stay hot long enough to cook in. If not, I'll add some Vermicrete and K-Rend again. If I can't get it up to temperature of course I'll have to add some. But if it works without - and if the K-rend doesn't crack and fall off - I've saved myself the relative aggravation of working with Vermicrete. And I won't mind displaying my failure here as a dreadful warning to others... Chas |
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jms
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Post by jms on Oct 27, 2014 12:59:17 GMT
Good plan.
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Post by cobblerdave on Oct 28, 2014 10:57:54 GMT
G'day Sorry that's not correct. " old school ovens" used insulation as well. The old roman ovens which they spread through Europe used volcanic rock, tuft , pumise and the like and even an airated clay to provide insulation. Volcanic rock had a thermal conductive value of anything from K .05 to 1.25 which isn't bad considering modern ceramic board is .04. K value is a measure of connectivity, the less the value the less it conducts thus the higher the insulation value. Whith those villages becoming towns and cities came the side draft ovens took over. Long metal bars made it possible to build bigger ovens which were able to take the strains of expansion and contraction. They were filled with DRY sand. The sand had a K value of 0.17 .WET sand has has a k value of 1.25 which means it losses it insulation value. Though this time clay ovens have been built and even those primitive ovens were insulated. Clay slip , liquid clay and straw. Animal dung like cow poo with clay. Saw dust and wood chips and clay. Whatever was available. The amount of effort to insulate meant a lower amount if wood was required to fire and maintain the heat to produce the baked goods required. It's no different today. Obtaining, drying, cutting stacking and storing take an amount of effort. Better to use your time actually using your oven and enjoying what you can produce from it . Just my take on insulation Regards dave |
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Post by chas on Oct 28, 2014 16:39:44 GMT
Hi Dave, good to hear from you again.
Interesting historic info there - ain't the ingenuity of the Ancients impressive? These oven-owners of old were without much else to cook on or in, so they prudently maximised the use, extended useful lifespan per burn with mass/insulation/whatever and saved fuel too. If you were a baker, you'd have to. Just at this moment over here there's a feeble tv programme based around the 1666 Fire of London and an attempt to show a baker's shop where the fire started kind of puts in perspective all of that. No doubt inner-city fuel supply was a problem - still is, I guess.
None of the above applies to me and I'm impatient. If I can get this oven up to pizza-baking temperature and bake a pizza in it, it'll do for the moment - and it'll do until I discover its limitations. If my baking aspiration changes I'll probably modify. If I fail with the pizza... well, I'll be modifying for sure!
So far, with daily burns of increasing duration and size - though still quite restrained - the floor cleared of ash has achieved 260c on the oven thermometer while the outside top of the dome was about 31c and the corresponding underside 206 at it's peak with the digi. I'll bung the oven thermo in the electric oven sometime to check its calibration - the floor didn't get above 200deg according to the digi. One of them may be carp!
Chas
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