Cob recipe?

I realise that it's impossible to give a so many parts of this: so many parts of that type of recipe, as everyone's ingredients are very different, but is there a ballpark end ratio to aim at of plastic to non-plastic constituents for the 'mud' component?

I have a very fine plastic clay with zero grit of any kind, so need to buy in sand/ballast to stiffen it up. (The local soil and immediate subsoil has too many stones to be very useful. )

Tia

Finally found what I needed in google books.