Fwd: Re: [Cob] Difference between cob and rammed earth (reinforcing)

[Ian Marcuse]

Reinforcing cob in earthquake zones is probably a good idea. Bamboo 
would work fine I think, embedded vertically would help to prevent 
shear failure. In our recent earthquake tests at UBC this year, the 
need for this type of reinforcment was quite clear. Mind you at a 7.2 
richter quake the cob held up briliantly without reinforcement, apart 
from straw. At a >9 richter, the building seriously failed, but 
without roof collapse. A 9 quake is however extremely rare. If you 
have bamboo, I doubt that it would hurt. Does anybody have other 
thoughts on this?

We hope to post a video of the quake test on the web soon

Ian Marcuse



>
>
>In response to Layth,
>
>The response is not that cob "can't" be reinforced with rebar, it's 
>that it doesn't need to be!
>
>Cob is a equivalent to adobe in consistency: clay and sand are 
>combined with water and straw.  The cob mix is then sculpted by hand 
>into a monolithic structure (unlike typical adobe construction where 
>dried bricks are mortared together with clay slip).  Since the straw 
>fibers in cob run through the structure, no rebar or other extra 
>reinforcement is needed.  Adding rebar would just increase costs, 
>plus moving away from the beauty and simplicity of building with 
>completely natural materials.  A testament to structural integrity, 
>there are Medieval cob buildings, standing safe & sound to this day! 
>Cob is also called sculpted, poured or puddled adobe.
>
>"Rammed earth", as I've understood it to be, consists of a mixture 
>of soil and portland cement, lightly wetted, then rammed in between 
>plywood forms.  Since the mix contains no straw, rebar is required 
>for structural integrity.  I think rammed earth isn't an accurate 
>name; actually this should be called "Rammed Cement-Soil" when 
>portland is added.  Rammed Cement-Soil turns out to be a rather 
>toxic and industrialized material.  Have you ever had cement burn a 
>hole in your skin?  Not fun!
>
>I hope this helps.  There are many good books on cob, the best I've 
>seen is the "Hand Sculpted House" by Ianto, Michael and Linda of Cob 
>Cottage Company...
>
>(Note to Shannon - How's the description of cob on the cob website? 
>Is it detailed enough to direct inquiries like this to the site?)
>
>Ocean
>
>Intaba's Restaurant, Corvallis, Oregon
>http://www.intabas.com
>
>Ahimsa Sanctuary for Peacemaking and Sustainable Living, Philomath, Oregon
>http://www.peacemaking.org
>
>
>On Dec 10, 2004, at 1:39 PM, laythss at yahoo.com wrote:
>
>>Hello all again,
>>   I would like to know the reasons (or possible reasons) why Rammed 
>>earth can be reinforced with re-bar whereas cob cannot.
>>
>>Any help is appreciated.
>>
>>Layth
>>
>>
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>
>
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