Smooth finish in Slic3r using Support Material How can I obtain a smooth finish like the one in this video: Easy and clean support material removal from 3D printed part., using Slic3r instead of Simplify3D? What settings do I need to change?
I'd say the clue is the material itself and the geometry of the object. But in terms of Slic3r settings you could experiment with:

(print settings >> support material)


pattern spacing (he has here something around 5mm)
pattern (I'd say the best for you is rectlinear)
contact z distance (choose 0.2 or close to that)
interface layers (here 0 (zero) for sure)
don't support bridges (this one depends on your geometry and if slic3r calculates something as a bridge or not)


All above is also connected (in a way) with HE temperature and layer height. Usualy the higher temperature (in a range for specific material) the better sticking between layers.