Refer to the above stats.
Federer is actually not that great on clay either - had to wait for a lucky break in Nadal pulling out few years ago during Roland Garros in order to complete his All 4 Grand Slam big daddy swoop. He's a technical / elegant player and struggles on clay in general against bashing ogres.
Ferrer is not a clogger by the way - crazy use of adjective! 29 ATP finals and titles combined and counting - fudging hell, pal - did he 'block' his way to all those. He's got a fantasic back-hand and moves really well on the base line
For a big clogger at the moment appears to be big Isner - classic smashing serve and volley basher