[Cob] Soil ratio

[Lance Collins]

On Sat, 29 Apr 2006, Jennifer Roberts wrote:

>Anyone have luck with a 10% clay to 90% sand ratio? The books say it 
>can be done, and I am making some test bricks, but would love to 
>hear from anyone who has indeed cobbed with 10% clay.


and Shannon responded


>Your actual clay/sand ratio is meaningless, with some clays it might 
>take 30% clay to make it work, and for others 10% might even be to 
>much.  It depends on how sticky your clay is, and that will vary 
>tremendously from one place to the next or even just from one layer 
>of your soil to the next.  When in doubt make test bricks, that is 
>the only way to be sure what you will end up with.

If you check Wikipedia you will find that:

>Clay minerals are hydrous 
><http://en.wikipedia.org/wiki/Aluminium>aluminium 
><http://en.wikipedia.org/wiki/Silicate_minerals>phyllosilicates, 
>sometimes with variable amounts of 
><http://en.wikipedia.org/wiki/Iron>iron, 
><http://en.wikipedia.org/wiki/Magnesium>magnesium, 
><http://en.wikipedia.org/wiki/Alkali_metal>alkali metals, 
><http://en.wikipedia.org/wiki/Alkaline_earth>alkaline earths and 
>other <http://en.wikipedia.org/wiki/Cation>cations. Clays have 
>structures similar to the <http://en.wikipedia.org/wiki/Mica>micas 
>and therefore form flat hexagonal sheets. Clay minerals are common 
><http://en.wikipedia.org/wiki/Weathering>weathering products and low 
>temperature <http://en.wikipedia.org/wiki/Hydrothermal>hydrothermal 
>alteration products. Clay minerals are very common in fine grained 
><http://en.wikipedia.org/wiki/Sedimentary_rock>sedimentary rocks 
>such as <http://en.wikipedia.org/wiki/Shale>shale, 
><http://en.wikipedia.org/wiki/Mudstone>mudstone and 
><http://en.wikipedia.org/wiki/Siltstone>siltstone and in fine 
>grained metamorphic <http://en.wikipedia.org/wiki/Slate>slate and 
><http://en.wikipedia.org/wiki/Phyllite>phyllite.
>
>Clay minerals include the following groups:
>    * Kaolinite group which includes the minerals 
> <http://en.wikipedia.org/wiki/Kaolinite>kaolinite, 
> <http://en.wikipedia.org/wiki/Dickite>dickite, 
> <http://en.wikipedia.org/wiki/Halloysite>halloysite and 
> <http://en.wikipedia.org/wiki/Nacrite>nacrite.
>        * Some sources include the 
> <http://en.wikipedia.org/wiki/Serpentine>serpentine group due to 
> structural similarities (Bailey 1980).
>    * Smectite group which includes 
> <http://en.wikipedia.org/wiki/Pyrophyllite>pyrophyllite, 
> <http://en.wikipedia.org/wiki/Talc>talc, 
> <http://en.wikipedia.org/wiki/Vermiculite>vermiculite, 
> <http://en.wikipedia.org/wiki/Sauconite>sauconite, 
> <http://en.wikipedia.org/wiki/Saponite>saponite, 
> <http://en.wikipedia.org/w/index.php?title=Nontronite&action=edit>nontronite 
> and <http://en.wikipedia.org/wiki/Montmorillonite>montmorillonite.
>    * Illite group which includes the clay-micas. 
> <http://en.wikipedia.org/wiki/Illite>Illite is the only common mineral.
>    * <http://en.wikipedia.org/wiki/Chlorite_group>Chlorite group 
> includes a wide variety of similar minerals with considerable 
> chemical variation.
You don't need to understand much of that to see that the word 'clay' 
is not very specific when you want a cob recipe.








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