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  #21  
Old 10-01-2008, 06:28 PM
Peasant
 
Join Date: Oct 2008
Location: Tanja
Posts: 25
Default Re: starting my clay oven.....................or maybe not.

Re Starting my clay oven.... or maybe not.
I'm the person behind the Low tech. oven as seen on the 'Better Homes and Garden TV Show' in Oz.
You saw 2 types of under floor materials.
The 1st one,seen in brief, was a layer of 'Hebel' blocks to prevent the heat escaping through the floor. Then you saw the packing of 200 mm of decomposed granite [packing gravel] in a 'well' in the oven base to act as a 'heat bank' to absorb the heat from the floor so that it 'gives back' once the fire is out or removed.
The untimate combination is to have a layer of insulation material down first [Hebel or Cal-Sil board or insulating bricks] then a decent depth of 'heat bank', then the oven floor.
You can see photos of some finished low tech. ovens at woodfiredovenworkshops.com
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  #22  
Old 10-01-2008, 06:39 PM
Journeyman
 
Join Date: Jun 2008
Location: Melbourne Australia
Posts: 399
Default Re: starting my clay oven.....................or maybe not.

Good to see you on this site Alan, when do the Tasmanian workshops start?
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  #23  
Old 10-01-2008, 07:11 PM
Serf
 
Join Date: Sep 2008
Location: Perth, Australia
Posts: 18
Default Re: starting my clay oven.....................or maybe not.

Quote:
Originally Posted by Wood fired oven workshops View Post
Re Starting my clay oven.... or maybe not.
I'm the person behind the Low tech. oven as seen on the 'Better Homes and Garden TV Show' in Oz.
You saw 2 types of under floor materials.
The 1st one,seen in brief, was a layer of 'Hebel' blocks to prevent the heat escaping through the floor. Then you saw the packing of 200 mm of decomposed granite [packing gravel] in a 'well' in the oven base to act as a 'heat bank' to absorb the heat from the floor so that it 'gives back' once the fire is out or removed.
The untimate combination is to have a layer of insulation material down first [Hebel or Cal-Sil board or insulating bricks] then a decent depth of 'heat bank', then the oven floor.
You can see photos of some finished low tech. ovens at woodfiredovenworkshops.com
Yes it is great to see you here mate.

I, for one am extremely gratful to you for this oven. I enjoyed the project, and I very much enjoyed our first pizzas last Sunday. It also cooks great naan bread.

THANK YOU!!
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  #24  
Old 10-01-2008, 11:18 PM
Peasant
 
Join Date: Sep 2008
Location: Melbourne, Australia
Posts: 45
Default Re: starting my clay oven.....................or maybe not.

I'd also like to thank you Alan. It was your design that first got me interested in building a WFO. I'm also using the BHG design, although just changing it slightly for where it goes in my courtyard, and using refractory materials from John, rather that the low-tech method.
BTW, is there something extra I need to know when using refractory cement rather than clay for the igloo?
Thanks
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  #25  
Old 10-02-2008, 02:50 AM
Peasant
 
Join Date: Oct 2008
Location: Tanja
Posts: 25
Default Re: starting my clay oven.....................or maybe not.

Hi Balthazar,
I've found the addition of a couple of cup fulls of stainless steel 'needles' [those used in the furnace industry] to a bag of castable is a fantastic reinforcement that eliminates cracking, even on a large dome.
John from Refractory and Ceramics P/L has them, but he may already have sold you some.
Wood fired oven workshops
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  #26  
Old 10-02-2008, 03:05 AM
Peasant
 
Join Date: Sep 2008
Location: Melbourne, Australia
Posts: 45
Default Re: starting my clay oven.....................or maybe not.

Quote:
Originally Posted by Wood fired oven workshops View Post
Hi Balthazar,
I've found the addition of a couple of cup fulls of stainless steel 'needles' [those used in the furnace industry] to a bag of castable is a fantastic reinforcement that eliminates cracking, even on a large dome.
John from Refractory and Ceramics P/L has them, but he may already have sold you some.
Wood fired oven workshops
Hi Alan. Yes, I've been to see John a few times already and I'm about to visit him again to purchase everything for the dome. Today I finished the cooking surface and surrounding pavers so I'm ready for the next stage. Hopefully I'll get to see John tomorrow
Have you got any idea of how many 25kg bags of refractory cement I'll need for the dome? It's the same size as your design on "Better Homes and Gardens"...or near enough.

Thanks
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  #27  
Old 10-02-2008, 05:39 AM
Peasant
 
Join Date: Oct 2008
Location: Tanja
Posts: 25
Default Re: starting my clay oven.....................or maybe not.

For our workshop high tech ovens [about the same size as the BHG oven] we use about 8 bags of castable, then a full roll of blanket and a 'cap' of ordinary cement/sand/stone dust concrete to build that up to cover all of about 30 -50 mm. thick.
You will see some photos at Wood Fired Oven Workshops.
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  #28  
Old 10-02-2008, 05:52 AM
Peasant
 
Join Date: Sep 2008
Location: Melbourne, Australia
Posts: 45
Default Re: starting my clay oven.....................or maybe not.

YIKES!!! 8 bags!!?? ($$$). How thick is the castable layer? I was going to go about 50mm thick? I also wasn't intending to go with the blanket. I was going to use Vermiculite with cement fondue mix straight over the castable to a thickness of about 75mm for the insulation layer. Would this still be ok? I'm pretty much following the BHG model, except with refractory materials.

Last edited by Balthazar; 10-02-2008 at 06:24 AM.
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  #29  
Old 10-02-2008, 06:33 AM
Peasant
 
Join Date: Oct 2008
Location: Tanja
Posts: 25
Default Re: starting my clay oven.....................or maybe not.

The 8 bags of castable should give you a 'hotface' coverage of 50-75 mm. but thicker better [$$$$].
Vermiculite is a good insulator but the insulation properties are diminished the more binder materials [fondu etc.] you add.
One advantage of 'ceramic blanket' is that it acts as a cushion between the hotface of the dome and the protective cap of concrete as an outer shell.
If the layers are all tight the expansion of the inner dome can 'shove' the outer layer into cracks.
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  #30  
Old 10-02-2008, 06:39 AM
Peasant
 
Join Date: Sep 2008
Location: Melbourne, Australia
Posts: 45
Default Re: starting my clay oven.....................or maybe not.

Thanks Alan. I presume John sells the ceramic blankets? I'll call him tomorrow.
I was intending a 4:1 mix of vermiculite:fondue. Is this a good ratio if I do choose to go with it?
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