Sci Fi Coaster

Saw a coaster and decided I wanted to make one. I used zbrush and created this design in 15 min. Repetier says .stl is non- manifold. but, sliced and printed fine.
Saw a coaster and decided I wanted to make one. I used zbrush and created this design in 15 min. Repetier says .stl is non- manifold. but, sliced and printed fine.