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  #11  
Old 03-25-2014, 06:57 PM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,756
Default Re: My First (hopefully last) build - Cast Refractory

In my case, because my flue gallery is so light I join it to the dome with refractory mortar and have a thermal break between the gallery and outer arch where temps are not as high, but you can place it between the dome and flue gallery if you wish. I use 4:1 (vermiculite, cement) vermicrete for this. Having the thermal break a bit elastic allows for some thermal expansion.
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  #12  
Old 03-26-2014, 05:43 AM
Apprentice
 
Join Date: Sep 2013
Location: Brisbane Australia
Posts: 127
Default Re: My First (hopefully last) build - Cast Refractory

Your oven is looking good. I did a cast refractory oven also. Its not as refined as David s's casting, but it does the job. Its about 2 inches thick in most parts, but thicker on the sides and thin next to the dome entry.

For the join to the dome I used a mix of sieved castable and vermiculite 5:1 first, but it started to fall to pieces, and replaced this with ceramic rope encapsulated in a sieved castable slurry. You want to minimise exposure to ceramic fibre.

I would be careful if your fire rope is not ceramic fibre. lots of glass fibre rope about, buts its only rated to 350 degrees. Ceramic is rated much higher. With fire coming out or the dome entry, it could get above 350 degrees.

The sieved castable and vermiculite 5:1 might work for you, but I moved the outer flue gallery accidentally during construction, and from that point on I had problems with it. The protected fibre rope did the trick.

My build at your stage of construction:
http://www.fornobravo.com/forum/51/n...e-19976-8.html (New 36inch castable build in Brisbane)


Cheers,
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Last edited by brissie; 03-26-2014 at 05:48 AM.
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  #13  
Old 03-26-2014, 07:26 AM
Peasant
 
Join Date: Jul 2013
Location: Debden Green, Essex
Posts: 27
Default Re: My First (hopefully last) build - Cast Refractory

Thanks David and Brissie,
I'll have to check what rope it is.
I do have some offcuts of body soluble blanket.
Some will be used over the vent arch, and I was planning to tuck a bit between arch and dome anyway, then shield it at the inside of the arch with vermicrete. (i could use some sifted castable)

Managed to get the blanket and vermicrete on the dome two days ago.

2" blanket all over, then I had enough to lay another 1" over the top from from to back (dome had a mullet hairdo)
Slapped about 1 1/2" vermicrete over that.
Fired it up yesterday - gentle fire for about 3 hours.
With no door and only a rain cover through the night - inside walls were still warm this morning. Only about 25degC (measured by touch), but gave me something to smile about.
I really can't wait to get a full burn on this.
I've had 6 curing fires so far, two since I put the insulation on. I suppose I'm going to need a few more when I fit the vent arch.
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  #14  
Old 03-27-2014, 12:50 AM
Peasant
 
Join Date: Jul 2013
Location: Debden Green, Essex
Posts: 27
Default Re: My First (hopefully last) build - Cast Refractory

Cast the arch yesterday.
I beefed up the design a bit and have about 1/2 a bag of refractory castable left.
If I sift this and don't have enough mortar for the thermal break, can I add a bit of fireclay to bulk it up? I have about 10kg of powdered fireclay.
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  #15  
Old 03-27-2014, 02:19 AM
david s's Avatar
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Default Re: My First (hopefully last) build - Cast Refractory

Quote:
Originally Posted by pikemonkey View Post
Cast the arch yesterday.
I beefed up the design a bit and have about 1/2 a bag of refractory castable left.
If I sift this and don't have enough mortar for the thermal break, can I add a bit of fireclay to bulk it up? I have about 10kg of powdered fireclay.
Yes, just replace the equivalent volume of aggregate removed, preferably with half sand and half powdered clay. Remember that too much clay in the brew means more shrinkage and therefore cracks.
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  #16  
Old 03-29-2014, 02:42 AM
Peasant
 
Join Date: Jul 2013
Location: Debden Green, Essex
Posts: 27
Default Re: My First (hopefully last) build - Cast Refractory

Arch fitted.
Joining faces were chamfered to provide a channel for insulation fill.
Used some cementone fire cement to seal the inner joint of the arch/dome, about an 8mm gap. Checkd with manufacturers (Bostik) who reckon this stuff is good for pointing up to 14mm, so we'll see.
From outside the 8mm to 25mm chamfered joint was backfilled with vermiculite/sifted refractory mix.
If this crumbles - the fire cement should hold it in. If the fire cement crumbles also - plan B (which I have yet to devise!).

Fitted a 7" flue pipe (3ft length). Experimenting so just used some tin foil jammed around it as a seal.
Had a firing - almost all smoke drawn straight up the flue from cold.
A few wisps out the front of the arch, but nothing much, and the whole flue arch is only 10" deep. Still not fitted a decorative arch yet, so time will tell.
Arch did not get very hot and it was a fair sized fire.
How much insulation would anyone recommend for the flue arch??
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  #17  
Old 03-29-2014, 04:02 AM
david s's Avatar
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Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
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Default Re: My First (hopefully last) build - Cast Refractory

Quote:
Originally Posted by pikemonkey View Post
How much insulation would anyone recommend for the flue arch??
It's the dome and floor in which you want to retain the heat, so as your flue arch doesn't get as hot anyway I think you only need enough insulation to act as an expansion joint so the expanding arch doesn't crack your outer shell. I don't use blanket over the gallery, just vermicrete.
Wow, you're going really well. I just checked when you started, less than a week and you're firing already. Folk who cut bricks often take over a year to build an oven. You don't have to convince me that a cast oven is way faster. What is your internal diameter?

Last edited by david s; 03-29-2014 at 04:12 AM.
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  #18  
Old 03-30-2014, 12:59 AM
Peasant
 
Join Date: Jul 2013
Location: Debden Green, Essex
Posts: 27
Default Re: My First (hopefully last) build - Cast Refractory

Switching to metric - internal diameter is 1 metre. (39 inch appx)
All door opening ratios taken into account,
Been a bit slack with the photos - will follow this up soon.

As said before - I work on ships, normally rotate 5 weeks away with 5 weeks leave.
So I suppose I have an advantage there over weekend oven builders, since I've been at it all leave. Away this week so been racing the clock!! Decoration will continue next leave, but oven is functional.
The ground slab was in place 6 months ago.

Had a couple of additional curing fires, then went for it yesterday afternoon!!! First pizza party with some neighbours - The Christening!!

350degC at the floor to cook pizzas. 400+ around the dome Heat up time, about 1 1/2 to 2 hours.

Cooked pizza, then ran it as a gentle open fire when the British evening chill set in.
No more fuel added after 1900.

Made a temporary "Blue Peter" door from one of the MDF forms, some tin foil, and some batten.

Oven temp this morning at 0800 was 180deg C dome and floor.

Outside of the dome reached 55degC in some places when at full temp and saturation. So I might add another 1" layer of vermecrete, or even some domestic insulation blanket. (The vermicrete will be easier, since it will be the final, painted rustic dome finish).

With the floor bricks saturated to 350 degC, underside of lintel base measured at 19 degC.
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  #19  
Old 03-30-2014, 01:38 AM
david s's Avatar
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Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
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Default Re: My First (hopefully last) build - Cast Refractory

Ceiling insulation compresses very easily which makes it hard to render against. Sounds like your oven is performing pretty well. Expect it to do even better after several more firings.
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  #20  
Old 03-30-2014, 05:24 AM
Peasant
 
Join Date: Jul 2013
Location: Debden Green, Essex
Posts: 27
Default Re: My First (hopefully last) build - Cast Refractory

Cheers David, I'm happy with it so far.

Since all the newspaper from the dome forming was well and truly incinerated last night I can now see the inside surface of the dome better. A bit hot to stick my head right in at the moment but only really seeing a couple of cracks which correspond with those from my over zealous curing before. Not affecting performance.

The fire cement I used to fillet the arch was a bit cracked at the arch top - expected that, can be touched up.
I noticed the flue arch was hairline cracked through before firing yesterday. Reckon this was done on moving it/removing the formwork (which was stubborn). But the arch is stable and self supporting.

Lessons learnt - a touch more patience required on the curing maybe.
Otherwise it is working fine, and I have room to improve dome insulation if required.

Planning to paint over the vermicreted dome, or put another layer of vermicrete on using white cement (snowcrete).
Any recommended coating/paint for sealing the outer surfaces when done?
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