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  #61  
Old 12-27-2009, 08:15 AM
Apprentice
 
Join Date: Jul 2009
Location: Cochrane, Alberta
Posts: 104
Default Re: Insulation Efficiency

What started me down the path of building a forno was a nostalgic thought of my Grandmothers clay oven on her homestead. Clay and straw or clay and sawdust have been proven over time as traditional building materials. I am not sure if they have the same insulative factor as cement and vermiculite but are probably excellent alternatives. If you have the space, just make the insulative layer thicker. One question though, will the material weaken as the the straw burns out?
I would stay well away from styrofoam as there would be chemical residue coming off of it for a long time. Keep in mind you are using this for food you are eating.....
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  #62  
Old 12-27-2009, 08:22 AM
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Join Date: Nov 2009
Location: Penn Valley, Ca.
Posts: 213
Default Re: Insulation Efficiency

We use wood shavings in our chicken coop. They are much larger than saw dust and would probably work well and they are inexpensive. $5 per bale.

Tom
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  #63  
Old 12-27-2009, 01:03 PM
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Join Date: Jun 2008
Location: Melbourne Australia
Posts: 399
Default Re: Insulation Efficiency

My only concern is, you wouldnt really be able to get up to a temperature to burn out the foam or woodchips without actually firing the bricks above say, 1000c+, which is what the brick manufacturers fire at.
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  #64  
Old 12-27-2009, 04:41 PM
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Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,833
Default Re: Insulation Efficiency

Pottery kiln builders sometimes use sawdust and clay mixed together as an insulating layer. It is highly unlikely that the sawdust will burn away,rather it will just dry and leave a lightweight pocket containing air. Clay is a much better insulator than cement (ever been in a mud brick house in mid summer? You'd swear it was aircond.) Clay is dense though and I suspect the mix would not be near as effective as perlite or vermiculite. Another material that is traditionally used is manure. I think because it contains a lot of undigested material (I'm thinking horse manure here) If you used a lot of chopped straw and mixed a minimal amount of clay and manure (just enough to make it hold together) you'd get a pretty lightweight and insulative mix. Allow it to dry really well before curing and stucco.
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  #65  
Old 12-27-2009, 04:49 PM
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Join Date: Dec 2009
Location: Christchurch, New Zealand
Posts: 78
Default Re: Insulation Efficiency

kiko denzer has written on his blog he had better results in the longer term with saw dust than long straw after the straw burnt out the clay began to compact causing a reduction in it's insulating qualities.
Regards
Bart
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  #66  
Old 12-28-2009, 07:04 PM
Serf
 
Join Date: Oct 2009
Location: Charlotte, NC
Posts: 22
Default Re: Insulation Efficiency

Talking to a ceramic engineer of 30 years, who is now in sales for a well know refractory supplier, I have worn him out with questions regarding every phase of the oven building. He told me that going with #8 Kaowool is really a waste of $$ seeing that #6 and #8 both have the same insulating properties until about the 1700F mark, at which time the #8 will continue to hold its own, but the #6 falls off slightly. Seeing that the #8 cost a great deal more, it is a lot cheaper to use two (or more) layers of the 1" #6 than to go with #8.

He has also sold me on a lightweight premixed 1900 deg-F Insulating Castable to render over the dome, It is 30 lb/ft^3 density and sold in 50# bags, @ $9.00 ea. Bang for the buck her is that this will cost less than $30 to insulate the dome, and on top of that I will still use 1 layer of #6 Kaowool.

Guys like this are good to talk to and have been in the industry forever and really know what works and what is a waste. They use these products day in/day out in high temp furnaces and kilns, so they see a lot of this as overkill when it comes to only 1000-F that we see in a typical firing.
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  #67  
Old 01-06-2010, 10:32 AM
Serf
 
Join Date: Jan 2009
Location: Clearwater, FL
Posts: 3
Default Re: Insulation Efficiency

First I want to thank everyone for providing such great information that helped me build my first oven. Also the folks in Florida for the help locating suppliers. I spent much time reading this forum and finally, voilą - completed the dome last week.

I'm at the point of insulating the dome with 1" blanket (Superwool), I'm concerned of placing the vermiculite/cement mixture directly over the insulating blanket (and chicken wire).
Could that compress the blanket so that it loses it's insulating properties?
What do yo think of these options:
> Aluminum foil or some other material between the blanket and vermiculite/cement?
> Using stucco metal lath instead of chicken wire to provide gap/support?
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  #68  
Old 01-07-2010, 12:04 PM
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Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
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Default Re: Insulation Efficiency

No the blanket is fairly firm and does not compress as the vermicrete is really light. Lots of people have followed this method without compressing the blanket. Some people use a foil layer, there are pros and cons for doing this, eg prevention of moisture loss into the blanket. This creates problems later by locking in moisture below the foil. I think (others may disagree) it's better to skip the foil. If you get the consistency of the vermicrete right it just sits there and dries without disturbance to the blanket.
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  #69  
Old 01-07-2010, 01:07 PM
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Location: New Jersey USA
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Default Re: Insulation Efficiency

Quote:
Aluminum foil or some other material between the blanket and vermiculite/cement?
The aluminum foil idea has been debunked again and again. There's no use for it in oven building except to create a non-adhesion layer between different masonry parts, for a slip plane. Since it decays in the presence of the corrosive mortar, it doesn't have any heat reflective properties.
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  #70  
Old 01-07-2010, 09:46 PM
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Join Date: Dec 2009
Location: Christchurch, New Zealand
Posts: 78
Default Re: Insulation Efficiency

Foil also stops Moisture from passing out, causing condensation between the thermal and insulating layer which can cause clay ovens to collapse and can't be good for brick/cast ovens either.
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