New 42'' pompeii build in Canberra

[david s]

Re: New 42'' pompeii build in Canberra

I'm undecided about whether the drying out fires should be done with or without insulation. There are advantages and disadvantages for each method
uninsulated- water is not trapped by the insulation layer, but refractory or brick is subject to greater temperature difference between inner and outer surfaces.
insulated-slower water elimination, but more even heat distribution.

My first oven had a floor brick half in and half out of the oven. It was a very high duty brick and I was surprised when a crack formed right down the middle of it. It was the only floor brick that cracked and although I'm not certain, I put it down to the fact that the temperature difference between the inside half and the outside half created too much stress because of the difference in expansion.
Uninsulated flue tiles are also subject to cracking because of the same effect.
You could be right and perhaps it is perfectly safe to fire an uninsulated dome. For now I prefer to fire after the insulation has been applied, but certainly wait until all the moisture has been purged before rendering over with a cement shell.

[oasiscdm]

Re: New 42'' pompeii build in Canberra

Goes to show David that keeping oven and landing completely separated has some merit. In my build I have done this meticulous. The oven and landing are not part of each other and insulated also. I even felt it necessary to insulate the landing and dome to keep temperatures as even as possible across the transition to minimize temperature variances. I think the combination [ shiralite and ceramic blanket ] works very well. Especially the order applied brick/shiralite/blanket. When saturated inside brick temps vs outside brick temps are identical. I feel the shiralite has assisted this as it is insulative as well as dense adding mass as you have previously pointed out David. I think method has assisted all round. Only change I would make perhaps 75mm of blanket next time.

Seems to work no cracks at all touch wood. Or maybe I've just been very lucky.

Back to topic fire after insulation but will add render if rendering only after completely dry. Apply a scratch layer, 10mm max, first then fire again a few biggies, just to ensure blanket is dry for this coat the thinner the better. Then apply to desired thickness.

[david s]

Re: New 42'' pompeii build in Canberra

"I feel the shiralite has assisted this as it is insulative as well as dense adding mass as you have previously pointed out David. I think method has assisted all round."

Perhaps, but you can't really have both. It's either dense and thermally conductive or light and insulating. What you have is something in between, not a great insulator but also not particularly conductive. Rather like an HB pencil that's not dark enough and not hard enough to hold a good point.

I still feel that you should place your best quality insulation against the inner dense refractory wall, but I'm sure yours will work ok, so keep cooking.

[oasiscdm]

Re: New 42'' pompeii build in Canberra

I understand your preference completely but each of 3 commercial oven/furnace builders I spoke too unanimously told me the order I used is the correct way. The shiralite David is also extremely light. But my main reason for the position was to lock dome bricks in place.

I have never found it logical to have blanket directly next to dome when everyone talks about bricks expanding and contracting. Then putting an extremely wet layer of vermicrete over the blanket. Makes no sense to me

Anyway either way obviously works, just not seeing the logic behind the normal approach.

[cobblerdave]

Re: New 42'' pompeii build in Canberra

Gudday Colin
You'd better explain what "shiralite" actually is .... Even my spell check doesn't recognize it.
Regards dave

[david s]

Re: New 42'' pompeii build in Canberra

Shiralite is an insulating castable made by Shinagawa. There are quite a number of different densities and different temperature applications, but as an example the medium weight product has a density of 1400 kg/m3 (1.4 kg/litre) this is pretty dense compared to perlite which has a density of around 100 kg/m3 (100 g/litre) The castable refractory I use has a density of 2000 kg/m3. (2kg/litre) much the same as brick. Generally the denser the material the more thermally conductive it will be.

Thermal conductivity of the Shiralite approx. 0.4 while the perlite is 0.03 and brick around 1.5

[Dan W]

Re: New 42'' pompeii build in Canberra

G'day Dan
How longs the dome been done for now? Recon the homebrew should be good and cured and pretty dry in the summer heat. You will not be suffering from steam cracks I bet.
If I were you I'd get myself some curing fires going now . Get that brickwork used to a bit of heat stage by stage..... Then have a pizza cook! No you don't need any insulation for that, just don't lean of the bare bricks after a couple of hours! Add the insulation later. I'm sure you'll have less cracks than someone trying to dry and heat temper the oven all in one go.
Regards dave

You got that right Dave! Laid the last few courses and keystone in 38deg (100F) heat last Wednesday and it's averaged 37deg for the most of the past week! There's a few hairline cracks in the mortar as I just couldn't keep enough water up to it - but I'm not fussed. No homebrew to speak of, but I am three days into my new job as Manager of the BentSpoke Brewing Co... so should be just fine on that front!

My full intention is to cure (just deciding heat bead or gas, tending the later as I've got all the gear on-hand), and then fire up big time for many pizzas with all the folk who've lent a hand building. Can't wait any longer! Any good threads on a curing regime someone can point me at?

Then to build the flue and entry arch (out of Canberra Reds of course).

Then to insulate in this order: brick --> fibre blanket --> vermic/concrete. I do not have Shiralite. Could be convinced to swap blanket and vermicrete order... can anyone point to any science/data on the topic to help me decide?

Then fire again to dry, before a render of (hmmm probably) bond-crete (any other recommendations gladly accepted).

And then maybe a decorative finish if I can find the time. All along the way - cooking.

Still not entirely sure how I'll do thermal break - but will do one somehow. To achieve a "no catch" floor - which is currently immaculately flat and smooth, I Was thinking of laying a thinish (50mm wide) line of vermicrete across the inner arch entry to within about 20mm of the floor surface, and then notching a 50mm wide "trench" across the base of some floor bricks to within 20mm of the surface - but after reading comments here - sounds like that would be a good chance of cracking due to in/out temp diff and heat/cool cycle. Thoughts?

Once again, thanks for all your thoughts/advice/views/opinions - love this forum!

[Dan W]

Re: New 42'' pompeii build in Canberra

Some pics from the build

[Dan W]

Re: New 42'' pompeii build in Canberra

more pics..

[cobblerdave]

Re: New 42'' pompeii build in Canberra

G'day Dan
Congrats on the new job.... There would be a few out there that would consider it there dream occupation!
My own thoughts on the insulation. 50 mm blanket is worth roughly the same insulation value as 100 mm of V- Crete, without the water. I've helped someone with a pearl-Crete insulation layer and its a shit to work with, cheap, which is good, but you have to let the stuff dry for ages. You have a dry dome so why not trust in the ceramic insulation you have if you want more insulation add more ceramic. You can render over ceramic insulation easier than trying the v-Crete then render.
I have no thermal break it allowed me to support the rear of the chimney on the front of the dome, I don't find I have a great heat loss.
A simple way to achieve a heat break is to place a spacer, say a couple of layers of 4 mm ply. Remove later and backfill with V-Crete later. On the floor I bed a length of angle aluminum or stainless in the V-Crete to give you a more durable surface.
On curing your oven there's a section on firing your oven give that a read its tried and proven.
Hope something here might help
Great work , love the pics
Regards dave

[oasiscdm]

Re: New 42'' pompeii build in Canberra

Hey Dave what about the curing vs tending conversation we had.

[Dan W]

Re: New 42'' pompeii build in Canberra

Hey Dave what about the curing vs tending conversation we had.

Is that in the public domain Colin? Link to thread?

Thanks for all that Dave!

[cobblerdave]

Re: New 42'' pompeii build in Canberra

Hey Dave what about the curing vs tending conversation we had.

G'day
Sorry Colin spell checks done the thing again . "Tending"
I'm going to take it means tempering.
Yes I still think there are three distinct processes going on when we "cure on oven.
The cement curing, a chemical reaction over time.
Drying out the water slowly the water you introduce when building so it doesn't turn to steam and put undue stresses on the structure.
Heat tempering the structure in incremental stages to its final operating temps.
Colin if I remember rightly you had fairly much dried each layer of you build so when it came time to "cure" you were disciplined and took your time and you dome is crack free.
Uninsulated domes dry fast and I eaten pizza out of 2 bare domes now with no problems . Insulated especially V-Crete are different, the water must be taken out slowly, teased out rather than driven out.
I've had my oven wet by the wheather on more than once. As long as your cautious and take it easy a couple of small fires will return it to a state which is not fully dry but dry enough to cook pizza without cracking anything. The dry ceramic insulation layer acts I think as an expansion layer and the vent on the dome allows the water to escape.

[Dan W]

Re: New 42'' pompeii build in Canberra

Congrats on the new job.... There would be a few out there that would consider it there dream occupation!

Aah, yeah, you're not wrong. Every time I wake up, I pinch myself to make sure it's still real! It's already fun, and the beer hasn't even started flowing yet - though the mash tun, kettle and fermentation tanks (all 8000L of them!) are in place and in the process of being all connected up as we speak. Then, I never, ever drink crappy commercial beer again. Looking at 18 different varieties of beer on tap with everything from cask conditioned real ales to lambics and hand-crushed cider. If you're ever in Canberra, do drop in. We'll be open from mid-April.

[Dan W]

Re: New 42'' pompeii build in Canberra

G'day

I've had my oven wet by the wheather on more than once. As long as your cautious and take it easy a couple of small fires will return it to a state which is not fully dry but dry enough to cook pizza without cracking anything. The dry ceramic insulation layer acts I think as an expansion layer and the vent on the dome allows the water to escape.

Thanks for all of this. Must admit, the argument of lack of water absorbtion in blanket (vs vermicrete) for both curing, and if(/when) the oven gets wet is an attractive property that might mean I should go get more blanket and do away with vermicrete entirely. Given the only underfloor insulation Ive got is about 120mm of vermicrete, what thickness of blanket do you think would be sufficient to retain heat in the oven to cook for days - as that is something I definitely want to aim for.

And thanks for the reminder about the vent in the render - had forgotten about that gold idea, which I agree is a very wise addition.