Good day from South Oz

[wotavidone]

Hi, my name is Mick and I think I want to build a wood oven. Its been harder than I expected to convince the missus that we desperately, desperately need a WFO.
Thanks to all the members who have posted pics of their pizzas and roasts, she has come to see my point. Providing I finish painting the house sometime soon, I can build an oven. Note that it wasn't the pics of the various architectural gems that tipped the balance, rather the culinary works of art. Well done, people.
In my town (north of Adelaide, South Australia), at least one third of the population has at least some Italian connection. So I am somewhat baffled as to why it has taken me 50 years to realise that to go through life without a WFO is to have a reduced existence.
Cost is an issue, plus my wife is keen to move to a newer house. She now thinks I can add value at our current place then, having learned from my mistakes, build an even better oven at the next place. Time, too, is always short when you work full time.
I was in Bunnings last Friday in Adelaide. They had a WFO diy kit on clearance for $999, but I hesitated, and left without it.
I've been mulling over the possibilities. One guy up here has an oven made from ordinary red house bricks cut to half the thickness and assembled with ordinary brickies mortar. When I mentioned that I'd read that such bricks and mortar wouldn't last, he shrugged and said "I try not to read too much"! Apparently the oven has performed well for many years. His only complaint - "it gets too hot".
I've read the Better Homes and Gardens adobe oven plans until the paper I printed them on wore out.
After much consideration and surfing the web, I've discovered this forum, with its wealth of ideas.
I have an idea for a reasonably quick, reasonably cheap oven, that I believe will work well.
Here is the plan:
My bro-in-law works at a steel supplier and can alert me when they have "seconds" steel on special. I have a 14 inch drop saw, and a welder, and I reckon I can whip up a solid stand very economically. The drop saw was a $30 cheapy from a garage sale, so it won't break my heart to put a masonry blade in it and cut bricks till it dies, either. Though it seems from reading the forum I might be able to greatly reduce the dusting by pre-soaking any bricks I need to cut.
I also have a concrete mixer, another garage sale cheapy, so I may cast a floor insitu, though I am toying with using a product called Hebel block. This is an aerated concrete building material available in blocks and sheets which is supposed to have an excellent fire rating and insulating properties. Have any builders in Oz used this material for insulation under the brick floor? How much weight would a 6 inch sheet support?
While in Bunnings I saw a massive, thick walled terracotta pot that is very nearly the right shape, it was about three feet across. I'm toying with the idea of using it with the right door shape, and there seemed to be no shortage of choice of various other terracotta pots from which to shape the front bit of the igloo.
I figure if they can make chimeneas from terracotta, a pizza oven is not out of the question. I'd put all this together with an external layer of the homebrew fireclay mortar, chicken wire reinforced, to add strength and mass. I reckon even the biggest terracotta pot is unlikely to be more than one inch thick, so I suppose I would need the added mass.
Then an insulating layer of the vermiculite and cement mix, though my boss insists his father always used clay and saw dust to keep the heat in his brick kilns.
I may take a lead from one of the forum members who has cast his whole dome from castable. This would be cost prohibitive for me, but doing the same things with the home brew mortar would not be.
Recently I was asked to dispose of some redundant castable at work. I was bitterly disappointed to read the data sheet which said it was chro-mag. I don't like pizza enough to risk cancer.
Clay pavers for the floor, as per the BH&G adobe oven plans.
Being an Oz build, assuming I ever make a start, then it will clearly require the liberal use of corrugated roofing iron, Tek screws, etc to impart the appropriate styling cues.
Lots of ideas bouncing around in my head.
I hope to make a start soon. If and when I do, I'll start a build diary in the appropriate area of the forum.
Regards,
Mick

[wotavidone]

I've just been in the local garden shop. They have some large pots that are 650mm/26inches across, and about 320mm/12.5 inches deep. Both dimensions are internal. They are almost dome shaped - have a flat base about 250mm/10 inches across, but the sidewall is curved like a dome. Best of all there is no drainage hole in the bottom to be plugged. There are some commercially made ovens being advertised at 700mm /28 inches across here in south oz, so I've been thinking that 650mm might just be usable.
The pots are "twice fired terracotta, which we call ironstone" according to the proprietor. I am tempted - they seem at least 25mm/1 inch thick, and also seem very heavy for the size, very dense indeed, so I reckon they'd be usable.
So here are the questions:
What the heck is "twice fired" terracotta? Any potters on the forum able to shed more light? It looks to me like this stuff has been fired to very high temps, much more fused than normal terracotta.
Would it cycle from cold to hot to cold without blowing to bits? If its properly insulated, it should cool very slowly?
Is 26" internal diameter and 12.5" internal height big enough?
I've seen some "flower pot" temporary experiments mentioned here on the forum, would it be worth doing a more permanent insulation?
I reckon this means the door must be about 8" high for the magic 63%, and at 26" internal diameter, I'm think the door should be 13" across?
Any comments/advice welcome.
Regards,
Mick

[cobblerdave]

hi
the pot idea sound interesting but the idea of an 8 inch 200 mm door doesn't same with the 26 in oven hearth. I built a forno brick dome 42 inch which is great plenty of room for pizza and dishes to fit through the door. ive seen the oven at bunnings and it looked a little 'dinky' to small for both a fire and a pizza. Try for something about 32 to 36 inches maybe. sorry not a home at the moment uther would figure out the door size for these and yes consider a sqaure door shape you can fit bigger dishes in.
Hebel can be an exceptable base insulation but being cement will break down over time in higher temps think of protecting it from heat with fb board or pealite layer on top. Yes I have Hebel as heath insulation in my oven no probs to date
The thinnes of the pot will not give you a good enough amount of thermal; mass to an oven. Pherrhaps use the pot as a base for covering of 1/2 brick commons and home brew heat mortar.
Again insulate the dome you got the mass you need now to keep the heat from escaping insulate the cheapest is probaly pearlite cement. dont be tempted to use house insulation unless you protect it from the hot bricks first so you may as well just use pealite
keep up a progresss report
this sound interesting sorry don't no much about pots

regards cobblerdave

[wotavidone]

G'day cobblerdave. After a bit of research I too am convinced a 650mm i.d. pot is too small. I was always going to add a layer of the homebrew mortar for extra mass, but the cooking chamber would just disappoint, i reckon. They also have a monster that is 900mm across, internal measurement, which I reckon is near enough to 36". All these garden joints stack their little pots inside their big ones, meaning getting one empty for a measure up is a challenge. With a pot that big I'd have no drama cutting the opening as per the FB pompeii dimensions, assuming the internal height is adequate. I reckon I'd get one of these plus one of those tall tapered sqare section pots. Wouldn't take that much thinking to figure out how to marry the two together so that the round one makes the cooking chamber and the square section one sits in front for a chimney. Main concern is how much they are. The big round pots are $180, up here in the country. An expensive experiment if I crack it cutting the door, or it cracks badly in use.
There is a bloke here in town who has cast several from refactory. Unfortunately he's made a couple of blues, I reckon.
1) His also look a bit on the small side. 2) The opening is very small both height and width. 3) The opening for the flue is in the main chamber, not out the front as per the ideal design. Funny thing is, he installed his own oven with vermiculite/cement insulation, with a rendered top coat, so he must have done at least a bit of reading first. He hasn't actually put his to the test with a pizza yet, but he's done roasts and chops in it.
One thing I don't yet understand is why perlite/vermiculite insulation is considered more durable than aerated autoclaved concrete. The perlite cement is still only held together with portland cement isn't it? What makes this more durable than the other?
I suppose anyone reading is wondering why I'm even bothering to chase up alternatives. Well its mostly because the more normal ingredients seem unprocurable here in town. I could probably pinch some stuff from work, but I'm kinda opposed to stealing from my employer, and its just about impossible to do it legit. Even a bag of fireclay seems out of the question, without a 5 hour round trip (not mention about $70 fuel) to Adelaide. Never mind, I'll keep thinking and finding out what can be sourced in town, for instance I was told of another business to see about firebricks today.
Regards,
Mick

[nissanneill]

Hi Mick,
Read Russell Javons' book, "Your brick oven, building it & baking in it",
ISBN 1 904943 25 X.
He has build numerous brick ovens and uses 2 of them commercially in his wood fired oven pizza restaurant down at Willunga. He uses only common red bricks for the dome and 2 layers orn2" fired clay pavers for the hearth,msee for an indepth look:

http://www.fornobravo.com/forum/f27/...alia-1930.html (Russell Jeavon's Pizza Restaurant - South Australia)

cheers.

Neill

[cobblerdave]

Dear Mick
Sorry about the quality of that last post, did it on an I Phone waiting around a hospital...don't worry everythings alright and It gave me something to do.

Pearlite... is like syrofoam beads light and full of air exept there volcanic rock
the cement is only used to hold them together till there covered by someother layer. So when the cement burns away it doesn't matter. Yes my oven has a Hebel layer under the hearth but if you go this way at least give it protection of a layer of pearlite on top

That pot price is a bit hexy you could buy a lot of brick commons for that. Cutting the hole would be a little nerve racking. If you find youself using one first experiment on a small cheap pot first. A square entrance would be better ..straight unfancy cuts. Mark out the entrance on the pot then drill largist hole in the corners ( not a hammerdrill ). Then use an angle grinder to cut up to the holes Not past them. the round corners will make it less likely to crack.

Why increase your thermal mass with fire proof cement? Why not use clay on the outside. The pots clay as well so less chance of cracking due to 2 different materials reacting differntly with heat. Checkout the local road cuttings when you see a layer that is below the topsoil take some home smash it down with a hammer soak overnight. Roll in into a finger size piece and bend it backwards over itself over your finger. if it breaks straight away...no good . If it bends most of the way and doesn't break great you found the right stuff. No I havent built an oven of clay I have made bricks for a house from it though. The mass of the oven can still be covered in pearlite and finally cement rendered to protect from the elements.

Its a great idea your making a steel stand as any failures can be scapped off and buried in the garden away from the brides prying eyes...

Regards Dave

[wotavidone]

Hi Neill,
I reckon I've done enough reading to build a brick oven in my sleep. The thing is, I just don't want to build a brick oven.
I honestly feel its too much messing about. What I've been doing is reading all the stuff on the forum here in search of the quick, easy and cheap things that still work. This is why I've perused the alternative ovens threads in some detail.
So far I've gathered some useful "facts" from this gold mine of a forum that I'll stick to:
*Thermal mass is vital. Heat from the flames of the fire is not what you are looking for when cooking a pizza, it must be radiant heat and direct contact transfer from the hot mass of whatever material you use.
*Should balance that thermal mass up, it looks to me as if the ideal is to have the floor and dome at the roughly same thickness. For example, if you have a massive dome and a thin floor, you won't get the dome hot enough without having the floor so hot everything burns. A thin dome/thick floor combo would probably mean that by time the floor is hot enough the dome is too hot.
*Shape is very important - after reading lots of posts on the subject, you would be very unlikely to talk me into anything other than the traditional domed igloo.
* Certain ratios are very important. So far, I've gathered the following
- door opening height to dome height 0.63
- dome height to diameter about 0.5, though this is variable according to the pompeii plans
- a door width of about 0.5 of the dome diameter
- haven't really worked out how long the igloo bit that you stiock the flue in should be as a ratio of the oven diameter, but logic suggests that if you have an 8inch/20cm flue its gotta be probably 30 cm long at the top?
* So, if I built an oven of 1 metre internal diameter, I'd make it about 50cm high inside, the door would be about 32cm high and about 50cm wide, maybe a little less.
*Insulation is vital - must be lots of it, so that you can have lots of heat without having lots of flames burning your pizza before it is properly cooked.
*Haven't quite worked out the flue diameter thing yet, except to oberve that if you make the hole too big, you can always marry it up to a smaller flue if you need to, but the other way round wouldn't be so easy.
*An observation I've made on my own, which I have not directly come across yet while reading the forum - fire bricks while not doubt being more robust than clay pavers, are nowhere near as heavy size for size - at least not the ones I've been handling lately. This no doubt needs to be taken into account when pontificating on how thick your floor should be, since we are talking thermal mass here. Clay pavers would do me fine, except I haven't spotted any with nice square edges, they are all nicely rounded off. I guess it wouldn't matter too much as cooking surfaces go.
Anyway, its all fun. I'm of out the back to clean up my yard, so I have somewhere to build.
Mick

[cobblerdave]

Dear Mick

Going brick great! whats with SA and pavers? Go commons (not House bricks full of holes)
If you havn't got a set of formo plans go to the forno shop and download a set for FREE. its all in there the bloody things massive and its all in there bricks, Mortar mixes, the lot

regards dave

[wotavidone]

Good day neill, looks like our posts are crossing over. I'm convinced on the perlite/vermiculite thing, now that you have given me an explanation that makes sense. I have been a little worried about seeing the whole lot sink into a collapsing floor. I didn't realise that whole point was to have something left if the cement burns away. At least the vermiculite would still be there. After the cement burns away from a Hebel block, all that is left is air. Can't see air supporting much weight!
I was looking at the strength issues involved with coating the pot with an extra layer, making me think I'd need something stronger than clay. For instance I thought maybe if the terracotta cracked, the mortar mix might hold the pieces in place.
There is a terracotta beehive oven being advertised. Apart from the fact the actual shape leaves a whole lot to be desired, at least its slightly reassuring that what I'm proposing isn't completely doomed to failure. The item in question seems outrageously expensive, but some interesting measurements come to light. It seems the wall thickness, which consists of inner terracotta layer, insulation layer and outer terracotta layer, is 5.5 inches total. At that rate they can't be using much thermal mass inside.
I'm also mindfull of the weatherproofing issues. But you've got me thinking. If the inner surface is a fired clay pot, and the outer surface is rendered properly, there is no weatherproofing issue really.
The other interesting thing that has been wobbling around in my head is the issue of somehow reinforcing your clay. Steel in the form of chicken wire sounds alright to me, but I've also wondered if anyone has used glass fibre. I've got a bit of chopped strand mat left from a boat repair job. I'm going to see if the sizing, the stuff that holds it together in a mat until you wet it with resin, is water soluble. If it is, maybe I can soak it off and end up with glass fibres to mix in the clay for reinforcing. Shouldn't burn away like some fibres, nor should the expansion coefficient be different enough from clay to be a worry. Researching fibre reinforced concrete on the web has so far yielded plenty of suppliers of the concrete, but I haven't found anyone who just supplies the fibres. Apparently the fibres normally used for the job are significantly thicker than those used for fibreglassing.
I'm getting enthused. I shall start acting like a G.O.F. (geriatric old fart) and haunt the garage sales, maybe I'll find an appropriate pot going cheap.
I like you point about round corners in the door cutout. It used to be the way to stop cast iron cracking further, drilling a hole at the end of the crack.

Dave, the thing with SA and pavers is, if you don't live in Adelaide, you might as well live on the flaming moon. So if you are up here in the country, mining, smelting or farming, that is actually producing something, the hardware shops only carry very high turnover items.
That does not include the following: fire cement, fireclay, vermiculite, firebricks, ceramic insulating boards or blankets, etc. Therefore, unless one wants to special order, leaving one at the mercy of a single retailer's discretion with regards to price and whatever freight rate he wants to screw one with, one trys to go with the alternatives. And believe me, they charge like wounded elephants up here. If you think finding the gear to build a pizza oven is hard, should have seen what it was like getting the bits to build a full size Dalek.
If you decide that you'll try to get to Adelaide and buy stuff, its two and a half hours to the northern suburbs by car, each way, so its take a day off work during the week. Not to mention each trip is a $100 outlay even if you don't buy anything other than fuel and food.

[david s]

hi Mick,
If you use clay to clad the terra-cotta dome it will crack as it dries and shrinks, which is not a major problem because it is just adding thermal mass not strength. I think you would be better to use standard concrete 3:1:1 agg. sand, cement with half the quantity of cement replaced with lime. This can be reinforced with fibres, but do't use the plastic ones, they'll melt. Also don't use normal fiberglass as it reacts with the cement. You need a special alkaline resistant fiberglass for concrete.If the cement in this layer fails then the lime takes over just like the poor mans mortar.
I agree with everything else you posted. but I can't see drilling a hole through that ceramic pot without using a hammer drill, you'll be there for three weeks. An angle grinder with a diamond blade is my first choice.