[Cob] Natural exterior finishes

[Rachel]

My father in law who travels to Mexico quite often, commented that he 
noticed the Mexicans use "something that's not paint" to coat the exterior 
of their house.  He was wondering what it is and where he could buy 
something like that.  I told him what I know about lime plasters and such, 
and I have some recipes I can give him, but just curious if any kind of 
natural plaster is available commercially.  I know you can buy milk paint, 
but it seems like I once saw somewhere online you could buy more of a 
plaster.  This would be going over cement stucco, and would have to stand up 
to the Las Vegas heat.
TIA,
Rachel