Not sure if this one has been found yet, but it was a surprise to me! One of the best hardcore mainstream mud scenes I have seen!

German guys cover a chick completely except the head in thick mud and then have sex with her.

http://xhamster.com/movies/4072436/marcela_miscla_mud_bath_dp.html

Not bad.

That was brilliant!

Funny thing: have a poster on the wall: "A tisztasag 1/2 egeszseg". It's hungarian and mean: "The cleanliness is half health" XD