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Kiko Denzer on Art

[Cob] straw in cob or concrete? what about bamboo

Robert Alcock ralcock at
Wed Aug 20 16:44:04 CDT 2008

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> Today's Topics:
>    1. Re: straw in cob or concrete? (Lance Collins)
>    2. Re: straw in cob or concrete? (Damon Howell)
>    3. Re: straw in cob or concrete? (john fordice)
>    4. Re: straw in cob or concrete? (john fordice)
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> Message: 1
> Date: Mon, 18 Aug 2008 16:12:04 +1000
> From: Lance Collins <collinsl at>
> Subject: Re: [Cob] straw in cob or concrete?
> To: coblist at
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> In my response to Ocean's comments I was reacting to his 'all cement 
> is bad' tone and saying things about concrete which conflict with my 
> experiences.
> I believe in using appropriate technology.  Concrete is a very good 
> technology and the fact that some people get the design and building 
> of their structures wrong does not support arguments against concrete.
> The principal problem with concrete is it's environmental impact 
> (which is one of the reasons this list exists).
> Straw might work as a concrete re-inforcement but to me it doesn't 
> seem worth the bother.  Once you have paid for your concrete for only 
> a little extra you can get some steel and also great confidence that 
> the steel and concrete will work together to give you a satisfactory result.
> For people building their own dwelling probably the only place where 
> concrete might be considered is for foundations or retaining walls 
> where ground water is a problem.
> Lance
> (in Aus)
Hi Lance

Just a thought. How about using bamboo (either whole stems or the 
branches, which could be cut up into pieces) for reinforcement in 
concrete instead of straw? Heck of a lot more tensile strength than 
straw (try breaking even a tiny little branch of bamboo by pulling on 
it. Can't be done). Also much better rough surface for gripping the 
concrete. I have used it in pouring concrete for a composting chamber, 
but can't say whether it "worked" in the sense that I haven't done any 
tests to compare its strength with other forms of reinforcement.

By the way, we are using concrete not just in the foundation of our 
straw bale/cob hybrid house but also in bond beams at first floor and 
roof level.

Good luck,