Saturday, June 3, 2017

Know your building materials #1 Cob (natures concrete)

Know your building Materials:


Cob is a mixture of sand, straw and clay, it is a natural concrete without the 
embodied energy and chemicals.

Cob has been a building material for hundreds of years all over the Earth.   Cob is 
low tech,  easy to use and safe to handle without gloves, in fact working 
with Cob directly with hands and feet feels great.

Generally Cob is mixed by at least two people by foot, (music helps).
A standard concrete mixer can be used to mix Cob but I prefer the old fashioned 
method because it is community based and less noisy!

The ratio of the three ingredients will vary from site to site depending on the 
soil conditions but a general recipe is:

One part clay to one part straw and three parts coarse sand.
The coarse sand acts as a binder, the clay is the glue and the straw provides 
tensile strength.

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