Experiment with recipes

[SSS Alive]

Eric Hart wrote:

>        So if my scheme to use a clay/straw floor will work, what kind of
>recipe should I use?  Steve of SSS said something about a ratio of clay to
>sand.  How does that translate into a recipe?  I realize that it takes
>experimentation but a recipe might help.  I'm also wondering if you need to
>extract clay from the soil you have or you can just shovel in any clayey
>soil you have on a site (and experiment with the amount of sand, etc. you
>need).  I believe Robert LaPorte has a method for extracting clay from the
>soil you have on site.  Would like to just shovel in soil and figure out a
>recipe rather than separating the clay from the soil.     

Eric,

In my experience, experimentation is key, as soils differ in composition.
For our soil, the best recipe that I've come up with is 1 part clay subsoil
to 3.5 parts sand, and add in some chopped straw in the base coats, or even
the finish coat if you'd like, say .5 parts.  

More clay and it starts to crack too much (thick applications and getting
the mix too wet make it crack, too).
More sand and it gets more crumbly, and doesn't hold together as well (or
doesn't stick as well for plasters.  A good final plaster coat mix works
well as a final floor coat mix, as well.  

Make a big enough form (for floor experiments) and mix full batches.  Keep
track of ratios. 
 
Use the soil you have as it is, as a base for your experiments.  You may
want to use the subsoil, though, since topsoil usually has a lot of organics
in it, which weaken the mixture considerably.  Usually you have to add sand
for plaster or floor mixes, so why go through the trouble of separating the
clay out of the soil?  Robert is probably separating the clay so he can make
a clay slip for the Leichtlembau.  

Keep moving forward

Steve Kemble
Sustainable Systems Support