[Greenbuilding] Cob as an alternative to spray foam sealant?

[Steve]

A couple of years ago I was talking with a relative about ways to
build structures with modern techniques and traditional (natural)
materials, and the subject of spray foam came up. Ever since then,
I've had the idea kicking around in my head to try a clay slip/perlite
mixture sprayed into wall cavities like gunnite or shotcrete, anyone
know if this has ever been attempted?

I know it wouldn't be nearly as airtight or as insulating as spray
foam, but it would be better than nothing and still completely
biodegradable. :)

-Steve
-- 
http://www.greengeek.ca