I need to take the top 2 mm or so off some external render.
I need it slightly lower than the rest of the surrounding render prior to
applying a finish which will build it up again.
My first thought was some tough sandpaper but the wall is presumably a
kind of fixed location tough sandpaper.
Chisel of any kind seems too brutal and unlikely to give a smooth finish.
Angle grinder likewise (certainly in my shaky hands).
AMD FX-6300 in GA-990X-Gaming SLI-CF running Windows 7 Pro x64