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  #31  
Old 02-02-2013, 08:57 PM
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Default Re: Alternative Insulation

I know this is going to spark some negative but constructive discussion, but here goes. This thread began as an alternative insulation that could be found in Uganda. Sawdust and clay has been used for insulation in cob ovens. Some have used sawdust and Portland cement, much the same way we use vermiculite/perlite and portland. I looked back on some older threads on this site. I saw on a few posts where it was noted that the sawdust would probalby burst into flames and be a tragic end to the oven. Many cobb builders would probably disagree. That is if the right type of saw dust, properly seasoned, were used. I found an old article in Popular Mechanics that might be of some interest to someone willing to experiment.
Popular Mechanics - Google Books
Mother Earth News
The Mother Earth article is easier to download, and also offers a 30 year follow up of the material and how it held up.
The article is about a combat engineer who discovered during the 2nd world war that diometreus earth, (dioamaceous earth, tripilite, etc.) in small amounts, could be added to a sawdust and portland mix to increase fire retardants . He built a home using this material looking for a cheap building material with greater insulation properties. Whether or not it is suitable for ovens, it is still an interesting read.
Sawdust, and I think that I read that, rice hulls have been used as an alternative for v/pcrete. Maybe, this substance can be used to make other indigenous materials safer for oven insulation.
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  #32  
Old 02-02-2013, 09:44 PM
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Default Re: Alternative Insulation

I am really new to this forum but I never shy away from throwing in my two cents. Like everything else--it is as good as you pay for!

What I have seen of "diatomaceous earth" recently, it is used as a wall treatment that absorbs indoor pollutants. I have seen it applied once inside a new structure and resembles a very fine stucco finish. It takes several days for the surface to harden- even though it is applied very thinly.

Any of the materials you mentioned may work very well (if) separated from the very high temperatures of the inside of the oven. One would have to assume if you could place a probe into the oven assembly and measure the temperatures as you move outward away from the "combustion area", they drop based upon the material used. If you were to use the sawdust,cement mixture for insulating then it would have to be located in an area significantly below the combustion point for the wood (or) used in an area where the wood is meant to burn away and leave the void as an insulator. In the case of cobb, the remaining material is a clay/sand mixture--rather than portland cement that breaks down at high temperatures.

Other materials may work as well, corn cobs, rice hulls, straw, walnut shells, etc. Just finding the right product for the right location, and take advantage of its characteristics.
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  #33  
Old 02-02-2013, 09:54 PM
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Default Re: Alternative Insulation

Quote:
Originally Posted by mikku View Post
I really like to know more about "K" factors. I searched last night for a long time to get anything--then could not understand the numbers when I saw them.
"R" values are understandable, "U" are inverse, but "K" is another bird???
Yes they are all measures of insulating capacity. If you look up thermal conductivity of various materials they usually use k values.
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  #34  
Old 02-02-2013, 10:06 PM
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Default Re: Alternative Insulation

Different twist-
This morning my wife and I had to make a trip to the grocery store. While there, I bumped into a person that I worked with a few years ago. I mentioned my current hobby project and he said that his hobby is pottery! I asked him how his kiln is constructed and he mentioned "Oya ishi" or "Oya stone". As it turns out, this material is quarried within a few kilometers from me in Tochigi prefecture- "Oya village". It is also seen everywhere around here. It is used for building stone walls, "old style - grain storage buildings called "Kuras", and even Frank Lloyd Wright used it on one of his projects..I forget which one.

Anyway, this guy's kiln is made entirely of "Oya Stone" and then is covered with earth. I did not have the chance to get exact details from him but it is an example of earth being used as an insulation. This "Oya Stone" must be some kind of a volcanic rock, but I need to research it more. He said that it can be cut easily!

Back in the world--as they used to say, "Sluggo", a friend of mine (from Maine) used to make "Bean Hole Beans"- by digging a trench in the ground, firing wood for a long time; then placing a ceramic pot containing the prepared beans into the coals/ cover everything up with ???? something and wait for the beans to cook. "Same insulation characteristics of soil".

(Reminds me of a story of a trap for catching black bear!) Ha Ha

The point being: just plain soil should be a good insulator if used in the right way!
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  #35  
Old 02-02-2013, 10:08 PM
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Default Re: Alternative Insulation

I would doubt whether the sawdust would burn. Given that there would be no oxygen there to fuel it. Perhaps the first half inch or so might get hot enough to char the sawdust, but I doubt whether any of the rest of it would be affected. I was doing some repairs on my mobile wood fired oven after a customer had been over firing it ("Let's see how hot we can get this thing"). Ther was a crack near the top of the outer shell which surrounded the flue pipe. Whe I built it, I surrounded the pipe with about an inch of 5:1 vermicrete and t o hold it in position I used a cardboard collar w hitch I left in place and rendered/stuccoed over. I fully expected it to have at least partially burnt away, but was surprised to find no sign of overheating whatsoever and this was after about three years of pretty heavy use.
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  #36  
Old 02-02-2013, 10:16 PM
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Default Re: Alternative Insulation

So David S--
The bigger the "K" the better conductor,
Smaller "K" better insulator? Would it also be listed by thickness?
Is this a "metric system value" ?
Old brain cells of mine must be a very small "K" value for knowledge absorption.

Is "R" just a USA/North American concept?
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  #37  
Old 02-02-2013, 10:25 PM
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Default Re: Alternative Insulation

Quote:
Originally Posted by mikku View Post

Is "R" just a USA/North American concept?
And also used in Oztralia.
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  #38  
Old 02-02-2013, 11:23 PM
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Default Re: Alternative Insulation

Forgive me for my stupidity!
I have a lot to learn-- did a google map search of Oztralia! What a huge place Australia really is! A few weeks ago there was talk about extremely high temperatures reported. Have things cooled down at all? We would usually be experiencing the coldest time of the year but the temps were somewhere near 18 deg C. yesterday. It was a pleasant change.

This is a funny forum- as you browse what is here, you begin to realize how small the world really is and how "the same" our goals really are. I wish governments would interact as friendly and constructively as the members of this forum.

cheers
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  #39  
Old 02-02-2013, 11:32 PM
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Default Re: Alternative Insulation

Quote:
Originally Posted by mikku View Post
This is a funny forum- as you browse what is here, you begin to realize how small the world really is and how "the same" our goals really are. I wish governments would interact as friendly and constructively as the members of this forum.
Unfortunately the world is run by politicians and not humans.
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  #40  
Old 02-03-2013, 01:22 PM
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Default Re: Alternative Insulation

Quote:
Originally Posted by mikku View Post
So David S--
The bigger the "K" the better conductor,
Smaller "K" better insulator? Would it also be listed by thickness?
Is this a "metric system value" ?
Old brain cells of mine must be a very small "K" value for knowledge absorption.

Is "R" just a USA/North American concept?
Mikku,
your answer is here
K Values - What does it all mean?

Last edited by david s; 02-03-2013 at 01:25 PM.
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