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  #61  
Old 02-08-2013, 12:44 AM
david s's Avatar
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Location: Townsville, Nth Queensland,Australia
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Default Re: Alternative Insulation

And just to muddy the waters or provide some clarity, as a general rule the denser a material is the more likely it is to have a higher thermal conductivity, although there are exceptions eg the thermal conductivity of lead Pb is 35 W/mK while that of aluminium Al is 250. Although their densities are Pb 11340 kg/mxmxm and Al 2712.
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  #62  
Old 02-08-2013, 12:45 AM
Master Builder
 
Join Date: Jan 2013
Location: Tochigi Prefecture, Japan
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Default Re: Alternative Insulation

Thank you ATK406!
Your narrative is precise, accurate and understandable. It is easy to follow and a joy to read. I will have to search out your previous postings to see more of what you have to say on other topics!
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  #63  
Old 02-08-2013, 01:37 PM
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Join Date: May 2011
Location: South Australia
Posts: 559
Default Re: Alternative Insulation

So, chaps, has poor old NeilB, who just wanted to find out if there was an alternative way of insulating his oven, yet been offered a viable option?

I reckon the hard part is providing the insulation under the floor, as this material also has to support some weight, so that's where I've been doing my thinking.

I believe, if you leave out the "let's blind 'em with science" thing, it still comes back to one fundamental point.
In broad terms, (and yes there are exceptions, points of order, subtleties, little niceties that make one better than the other, etc) the insulating materials we might use for an oven are generally high melting point substances arranged in such a way that they trap a lot of stationary air.

What makes vermiculite, aerated concrete, pumice or bottles useful? Lots of air spaces.
I still think, if he can't get something like vermiculite or scoria, which have lots air spaces within the particles, his next best option is to use a material which has lots of air space between the particles.

I've thought about this and suggest that ordinary sand will not be very good. Not because a sand particle per se is a good heat conductor, though it probably is, but because if you you just go and dig up some sand then you will probably have particles of greatly varying size, so when it's laid under the floor, it won't have as many air spaces as you'd like to see, and lots of contact area for the sand to conduct heat away from the floor.

We recently drilled quite a few boreholes for water. The drillers use a graded sand to go around the bore casing. It supports the sides of the borehole and the casing, and at the same time is very porous to allow water to percolate through.
That sand had very even particle size, about 3-4 mm in size (say 1/8 inch or just over) and a layer of it supports a lot of weight without losing the porosity when packed down.
If I could get nothing else, I would get some sand, wash it to float out any organic material, clay or silt, then screen it through a quarter inch screen. Then I'd put the stuff that is less than quarter inch over an eighth inch screen, and keep the stuff that didn't go through..
This would give me a sand graded to minus 1/4 inch, plus 1/8 inch.
If I had nothing better, that is what I'd use under the floor.
mikku likes this.

Last edited by wotavidone; 02-08-2013 at 01:39 PM.
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  #64  
Old 02-08-2013, 03:27 PM
Master Builder
 
Join Date: Jan 2013
Location: Tochigi Prefecture, Japan
Posts: 620
Default Re: Alternative Insulation

"I think a Great Answer!"

Not because you reinforce my premise, but because you clarify your reasoning process.

I like the straw and rice-hull suggestions as well. All meet the criteria of "normally abundant, not site specific to any region of the world, and cheap"!

All are viable solutions that would work. Maybe not to the expectations of really serious WFO builders seeking perfection, but none the less workable!

The "if it were my choice in the same situation" answer --makes it honest!
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  #65  
Old 02-08-2013, 04:00 PM
Master Builder
 
Join Date: Jan 2013
Location: Tochigi Prefecture, Japan
Posts: 620
Default Re: Alternative Insulation

"Muddy river", "Clear water" da da da -reminds me of my youth and the last time in an "academic environment"--it sent me scrambling to Google-Periodic Table of elements and I found that it expanded greatly since then. I thought of elements with similar properties...then it got into protons, shells, electrons...quantum and my eyes glazed over..again! Physics, Geometry, Geology, Chemistry could not hold my interest long enough then--because I couldn't perceive their importance in the real world.

Quite the opposite though!

But... "where do you come up with these facts"?

Gotta say something though, this forum really makes you think!
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  #66  
Old 02-08-2013, 10:23 PM
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Default Re: Alternative Insulation

Quote:
Originally Posted by david s View Post
And just to muddy the waters or provide some clarity, as a general rule the denser a material is the more likely it is to have a higher thermal conductivity, although there are exceptions eg the thermal conductivity of lead Pb is 35 W/mK while that of aluminium Al is 250. Although their densities are Pb 11340 kg/mxmxm and Al 2712.
Sorry Mikku,
I was not intending to be confusing. My point is that usually dense materials are better conductors (poor insulators) so if you were looking for an alternative insulating material then probably start by looking for something that's not too dense. But be careful because there are exceptions.
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  #67  
Old 02-08-2013, 11:11 PM
Master Builder
 
Join Date: Jan 2013
Location: Tochigi Prefecture, Japan
Posts: 620
Default Re: Alternative Insulation

No apologies in any form are required or expected. No sarcasm intended, a simple celebration of the vast amount of knowledge floating around this forum.
Because of my inadequate knowlege of Japanese, I thought an intelligent conversation could only be had in my location by "talking to oneself". But to others it is viewed as a sign of dementia. Oh! Excuse me, What did I say?

Apologies to my other learned acquaintence in Oz!
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  #68  
Old 02-10-2013, 02:49 PM
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Join Date: Jul 2012
Location: Michigan
Posts: 201
Default Re: Alternative Insulation

Quote:
Originally Posted by NeilB View Post
Hello cooks and cobblers!

I am attempting to build a wood fire oven in Uganda ....... I'd appreciate suggestions of more commonly available materials that could function as decent insulating material.

Thanks!
Hello Neil,
If you have not done so already, I would read the thread titled "Hello from Uganda". There is alot of information there and it sounds like the oven is working great. I don't know how to post a link from that thread to this one but if you do a search under Uganda you'll find it.
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  #69  
Old 02-10-2013, 09:20 PM
Master Builder
 
Join Date: Jan 2013
Location: Tochigi Prefecture, Japan
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Default Re: Alternative Insulation

ATK406,
What a great reference.
Amazing to see what someone with a limited amount of resources can accomplish! And then put those efforts to good use helping others!
All our worries of builds to perfection, aesthetic qualities! Argh! Wish I had the courage to commit to something constructive like this lady has. Bravo to her!
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  #70  
Old 02-10-2013, 09:39 PM
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Join Date: Jul 2012
Location: Michigan
Posts: 201
Default Re: Alternative Insulation

Yes terrific forum isn't it? Best site on the web...if you're into WFO cooking! I'm honored to have joined such a group of talented people. A lot of great work done here....past, present....and future.
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