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chunked concrete for base?

 
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So, I plan to build my cob house this summer. Its been two years of planning. However, I am caught with a new prospect of having lots of broken concrete to deal with after a drainage pipeline running through the property was redone this past summer. Is it feasible to break it up in 15-20lb chunks and set that as the foundation for the cob build? What issues might I run into with that?

I am brand spanking new here to the forum and giddy with excitement over finding such a cool place to chat with likeminded people!
 
pollinator
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Yes and no!
If the broken concrete is set on ground that will not settle, then yes.
If the ground has topsoil etc left it place, then settlement will occur and the cob wall may crack.
 
pollinator
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Hi Maine. Welcome to Permies! I suspect you've found the right place.

I like John C's approach. Heavy clay could work; sand is tricky; and topsoil is jello. I know that one-man motorized tampers can be rented for jobs like this. But my experience with cob is minimal.

Hang tight. Lots of cob wizards around here. I'm sure they will chime in.
 
master pollinator
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Chunked concrete is also called, "urbanite." If you Google "urbanite cob images" you will see many creative ways to use the material for cob foundations. Urbanite is the foundation for the adobe buildings here and was also useful for creating the trough for a rebar-reinforced concrete bond beam or foundation (like knock out block).  Have a wonderful experience with your cob building project, Maine Fout!
 
Maine Fout
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thanks very much, folks!
 
Douglas Alpenstock
pollinator
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Amy Gardener wrote:Chunked concrete is also called, "urbanite."


I had forgotten that. Great word. Thanks!
 
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Yup urbanite can certainly be used as a stem wall to protect cob from moisture in the ground seeping up. Make sure to build that on a proper foundation, perhaps a rubble trench or having that stem wall deeper than your frost line.
 
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Not sure how well it will pack but I can tell you snakes . If you can't seal it your making a habitat for them could be I don't like snake
 
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The Cob Cottage Company uses urbanite in their buildings. They build on a rubble trench.
In the workshop I attended, they also taught me that, as a monolithic material, a cob wall supports a dry urbanite foundation as much as the foundation supports the cob.
 
John C Daley
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https://www.cobcottage.com/
 
The only taste of success some people get is to take a bite out of you. Or this tiny ad:
Building a Better World in your Backyard by Paul Wheaton and Shawn Klassen-Koop
https://permies.com/w/better-world
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