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  #61  
Old 02-05-2014, 04:23 PM
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Default Re: New 42'' pompeii build in Canberra

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Originally Posted by Dan W View Post
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.
G'day
The standard is 50 mm ceramic or 100 mm V-Crete ". You have 120 mm on the bottom ." Plentiful sufficiency" I'd say. Aim for 50 mm blanket any more a bonus. The stuff I used a box of 25 mm gave me 50mm over the dome.
You might find yourself spending a bit of your " beer pocket money" with the new job you'll have nothing to spend it on... Lucky bugger
Regards dave
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  #62  
Old 02-05-2014, 07:56 PM
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Default Re: New 42'' pompeii build in Canberra

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Originally Posted by cobblerdave View Post
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
I prefer the thermal break to be between the flue gallery and the outer decorative arch. If the gap is made of a material like vermicrete it will also act as an expansion joint so that the whole inner oven, gallery included can expand and contract completely independently from the outer shell which includes the outer decorative arch. This way you can still have your flue gallery insulated and integrated into the dome for strength and support of the chimney.
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  #63  
Old 02-06-2014, 12:49 AM
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Default Re: New 42'' pompeii build in Canberra

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Originally Posted by Dan W View Post
...
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!
I did two thermal breaks

It may give you some ideas. I put a 2 to 3 mm gap between both inner and outer breaks. I filled the inner one with ash, and the outer with sieved vermiculite/cement mix, at the upper part of the join.

You can feel the heat difference between the 3 sections, if you put your hand on or near the brick and tile surfaces.

Some photos...
Attached Thumbnails
New 42'' pompeii build in Canberra-dsc01749.jpg   New 42'' pompeii build in Canberra-dsc01754.jpg   New 42'' pompeii build in Canberra-dsc02058.jpg   New 42'' pompeii build in Canberra-dsc02059.jpg   New 42'' pompeii build in Canberra-dsc02060.jpg  

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  #64  
Old 02-06-2014, 02:31 AM
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Lightbulb Re: New 42'' pompeii build in Canberra

G'day Brissie
Great pics noticed something that lit the lightbulb. You also have a tiled surface at the entrance, right. I know one oven that has tiles but no thermal break. Quess what ... Broken tiles ! They don't like the heat, and I recon its important if you are to use a tile surface that you do build in a thermal break to protect them from the heat.
G'day Davids
Like the oven in your avitar the thermal break behind the decorative entrance and in front of smoke chamber and chimney means the oven is pretty much totally insulated from the outside. That not really common for a igloo design but more achievable in a doghouse design. My entrance protrudes to much for that to work I recon. To late for mine. But now I understand and appreciate the design of your ovens
Regards dave
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  #65  
Old 02-06-2014, 03:34 AM
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Default Re: New 42'' pompeii build in Canberra

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Originally Posted by cobblerdave View Post
G'day Brissie
Great pics noticed something that lit the lightbulb. You also have a tiled surface at the entrance, right. I know one oven that has tiles but no thermal break. Quess what ... Broken tiles ! They don't like the heat, and I recon its important if you are to use a tile surface that you do build in a thermal break to protect them from the heat.
G'day Davids
Like the oven in your avitar the thermal break behind the decorative entrance and in front of smoke chamber and chimney means the oven is pretty much totally insulated from the outside. That not really common for a igloo design but more achievable in a doghouse design. My entrance protrudes to much for that to work I recon. To late for mine. But now I understand and appreciate the design of your ovens
Regards dave
Thanks Dave,

The heat isolation is good, with the two breaks. The front tiles only get warm and mostly from the radiant heat from the fire.

I cooked pizza on Sunday, closed the door about 400c, next day Monday still had 230c cooked a roast, next day had over 100c and toasted muesli. thats 3 days above 100c.

I think the heat breaks and good insulation are the reason. I think it pays in the long run if you plan to reduce heat loss.

Steve.
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  #66  
Old 02-06-2014, 06:04 AM
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Default Re: New 42'' pompeii build in Canberra

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Originally Posted by cobblerdave View Post
G'day Davids
Like the oven in your avitar the thermal break behind the decorative entrance and in front of smoke chamber and chimney means the oven is pretty much totally insulated from the outside. That not really common for a igloo design but more achievable in a doghouse design. My entrance protrudes to much for that to work I recon. To late for mine. But now I understand and appreciate the design of your ovens
Regards dave
In my case because of the way I've designed the floor I was unable to put a heat brake/ expansion joint between the oven and flue gallery at floor level. Becsuse I made th flue gallery quite light (11 kg) there is little thermal mass in it to zct as a heat sink. Seems to work ok.
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  #67  
Old 02-06-2014, 12:31 PM
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Default Re: New 42'' pompeii build in Canberra

G'day
And if you don't have a heat break?
Mine doesn't I didn't have the knowledge or the skills when building mine. I'd don't believe the entrance is a big heat sink robbing the heat from the oven, nor radiating the heat away like the fins on a motor bike engine.
I think that an oven without a heartbreak has something else that comes into play. The entrance and flue is preheated by the radiant heat from the fire and the hot flue gases.
Anyway I'm still able to get the oven to pizza temp in a goodly time frame (2 hrs) maintain that, close of the oven with an insulated door to bake at 200C to 250C next day, and still have 100C to 120C the day after that.
That's not dissimilar to most other ovens that I'm aware.
So its a good and sensible thing to have, lack off will not cripple an oven. It seems to always come back to one thing , lack of insulation is the main thing to stop an oven working efficiently.
Regards dave
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  #68  
Old 02-06-2014, 12:55 PM
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Default Re: New 42'' pompeii build in Canberra

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Originally Posted by cobblerdave View Post
G'day
And if you don't have a heat break?
Mine doesn't I didn't have the knowledge or the skills when building mine. I'd don't believe the entrance is a big heat sink robbing the heat from the oven, nor radiating the heat away like the fins on a motor bike engine.
I think that an oven without a heartbreak has something else that comes into play. The entrance and flue is preheated by the radiant heat from the fire and the hot flue gases.
Anyway I'm still able to get the oven to pizza temp in a goodly time frame (2 hrs) maintain that, close of the oven with an insulated door to bake at 200C to 250C next day, and still have 100C to 120C the day after that.
That's not dissimilar to most other ovens that I'm aware.
So its a good and sensible thing to have, lack off will not cripple an oven. It seems to always come back to one thing , lack of insulation is the main thing to stop an oven working efficiently.
Regards dave
Yes, I agree with you. I believe that the heat break as an expansion joint to reduce the tendency to forming cracks in the outer decorative arch or the igloo shell is a far more important reason, unless of course you like having cracks on the outside of your oven.
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  #69  
Old 02-06-2014, 01:30 PM
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Default Re: New 42'' pompeii build in Canberra

Hey guys I'm curious with your heat retention figures. after pizza I Chuck 3 more pieces of wood in. Let it burn for around 90 minutes. Remove the fire, now I haven't got a door but use some hebel and Calsil, in entrance.

Following day I get around 300 - 350c, from there it drops around 60c per day.
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  #70  
Old 02-06-2014, 03:24 PM
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Default Re: New 42'' pompeii build in Canberra

That's pretty awesome heat retention in my book. I haven't built an insulated door yet (don't ask me what I'm waiting for), but I usually loose more than half my heat in the first 12 hr period (with the door closed) and half again over the next 24. That is dropping from around 450C to 200C in the first 12 hrs (that is still more than enough to cook with), and then again to about 100C by the next day.

I also have not finished my exterior yet (only a simple dog house covering the vermicrete render that I applied to my ceramic blanket). All told I only have 65mm of calsil under the floor (wish I had more but it was expensive) and about 90mm of insulation on the dome. I also do not have a heat break or insulation around my landing/vent. I hope to improve the heat retention with an insulated door and another inch or two of vermiculite on the dome but I don't think it will do much. Maybe I should put some vermicrete around the entry way too.

If you are only losing 60C per day I would say you must have one of the most well insulated ovens out there – Good Job.

Regards,
AT
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