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

[ocean]

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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