The Collaborative International Dictionary of English v.0.48:

Sloppy \Slop"py\, a. [Compar. Sloppier; superl. Sloppiest.]
   [From Slop.]
   Wet, so as to spatter easily; wet, as with something slopped
   over; muddy; plashy; as, a sloppy place, walk, road.
   [1913 Webster]