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Old 08-30-2007, 06:41 AM
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This could open up a whole host of cheap options for the insulating layers.
I will call past the garden supply and get some samples and do a few tests. Might reduce an oven by Aus$100 or so.
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  #12  
Old 08-30-2007, 07:37 AM
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Default Re: Lava?

Yeah

That is what I am thinking.

And I'm trying to build on the cheap.... 5 kids at home




Plus I wanted a stronger insulating layer under my dome.

I think this may work, I'm gonna try to build some test blocks tonite.
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Old 08-30-2007, 11:26 AM
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Default Re: Lava?

I'm not sure the blow torch test is relevant - the time factor with a pizza oven is a bit different. I tried to find comparison K values for lava, the only one I could find with google showed a K value around 2, compared with 0.5 for superisol and about 0.6-0.7 for perlcrete or vermiculite cement. I was unable to verify (tried searching here for the old discussion of K values but could not find it) whether these are the same units. I'd do a bit more background work before moving to a different insulation material - is perlite or vermiculite really that expensive by comparison?

Marc
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Old 08-30-2007, 01:07 PM
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Default Re: Lava?

I found a study that showed the k value of a cement/scoria mixture. Man that took a while.

The study found that k values range from .252 - .174 depending on the ratio of materials.
So I think it looks pretty good.

Here's a link to the study. K values are on page 10 I think.

http://www.academicjournals.org/IJPS...ep/Hossain.pdf

Thanks for the input, I would never would have thought about looking into K values.
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Old 08-30-2007, 01:28 PM
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Default Re: Lava?

Here are some pics of me blow torching a piece of lava rock/scoria (Thanks Bacterium!)

These first few are with the flash on.
Attached Thumbnails
Lava?-hand-showing-torch.jpg   Lava?-hand-showing-torch-2.jpg   Lava?-hand-showing-torch-3.jpg  
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Old 08-30-2007, 01:31 PM
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Default Re: Lava?

To show how hot this piece got I had some shots taken without the flash.

Thanks to my daughter Harley for taking the pictures.

I was still holding it with my hand for several minutes.

It never got hot on the other side.

I figured out the ratios, and it looks like 2 parts water 5 parts lava rock and 3 parts cement gives the best k value.
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Lava?-glowing-rock.jpg   Lava?-glowing-rock-2.jpg   Lava?-glowing-rock-3.jpg  
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Old 08-30-2007, 03:55 PM
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Default Re: Lava?

I like the ingenuity of this forum…..

Thanks Dave,
It sounds like you have a similar situation to me in that the oven is not seen as much of a “financial priority” so I had to be resourceful with mine as well
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Old 08-30-2007, 04:57 PM
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Default Re: Lava?

Green Home Building: Natural Building Techniques: Lightweight Concrete

"Pumicecrete" has an R factor of ~ 1.5 / inch.


Edit: Note to self - read both pages first!

<insert slapping forehead smilie here>
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Old 09-08-2007, 04:29 PM
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Default Re: Lava?

I'm still thinking about using lava rocks..

I took a bunch and made a brick out of lava rocks and cement. Then I let them cure a few days.

The only test I could think of was putting half of the brick in my gas BBQ. So thats what I did.

The bbq was over 600 degrees F and the half brick on the inside was hot enough to turn water to steam, but the half brick sticking out was still cool to the touch.

I think it would work fine! Just don't want to make an insulating error.
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Old 09-10-2007, 07:30 AM
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Default Re: Lava?

I'm anxious to hear how the final product works out. I bet the insulating layer with lava will have more strength vs the vermiculite which would make it a better platform for building on top of. I think I read somewhere that the vermiculite concrete wasnt very strong and wouldnt hold an anchor bolt.

thanks for doing all the research.
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