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The nature of Cob

Posts: 140
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There are  so many projects using cob in this forum that I would like to start a discussion on the basic nature of the stuff and practical facts for it's use.  For instance, can wet cob be applied to dry cob, or does a cob stricture, oven, RMH, etc need to be finished all at once?  How much heat does it take to "vitrify" (not sure this is the right word) cob?  Does it shrink?  Is it weather proof, or can it be made weather proof?  Are there any good web sites that discuss this?

Posts: 95
Location: Ferndale, MI- Zone 5b
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good subject!!!  i can't wait for some good resources!!!
Posts: 148
Location: South Central Idaho
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The one thing I remember from here .. or the book .. is that it takes one hour of heat .. to heat the first inch of cob .. does it take longer or shorter to heat the second inch?

I'm about to have a 16x24x37 metal box constructed with built in flu controls added by a sheet metal shop and will fill it with basalt rocks. It will have a removable top so I can add and subtract rocks to get a 100 degree exit temp when I'm normally firing my stove to 350. I hope to go for four to six hours during the night without having to get up and .. "feed the fire."

If this plan gets the house too hot while charging the rocks and they cool off too fast .. I will have to play with cob outside if it gets us too hot .. or a clay fire brick liner inside. I have a Chinese Fire Jet that I could put a flue on instead of a pot and do away with my soapstone and just fire this thing directly and with less wood. Don't think I'll do that .. would rather design my own Jet to burn scraps of 2x4 and tree wood .. get a shorter burn, more draft, much easier to "tend" or fire using the self feed of longer vertical wood instead of a horizontal constantly watched type Jet, better air flow as the fuel can not interfere with the incoming air flow of the vertical feed, it has its own air entry with its own controls. I may be able to rob the insulated vertical Chinese chimney .. it is pretty neat.
Posts: 278
Location: Iowa, border of regions 5 and 6
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Dusty, you're talking about the R-factor.  Cob has an R-factor of 1, meaning it takes 1 hour for 1 degree of heat to go through 1 inch of material.  If you have a piece of cob 12 inches thick, it will take 12 hours for that 1 degree of heat to make its way through. 

The greater the heat, the faster it's going to make its way through to the other side.  Cob is NOT a good insulator; however, it does hold heat (or lack of heat) very well.
I can't beleive you just said that. Now I need to calm down with this tiny ad:
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