bungie
I use a 125mm angle grinder with a diamond blade, then out with old faithfull my Ramset Dynadrill. I have seen a tool that looks like a planner with 4 tungstan blades inside it that grind out a trench in the wall. But the dust created was so bad, only your labourer could use it 
DISCLAIMER
All advice is given with-out seeing the job, and hence all advice MUST be taken as advice with limited knowledge on the exact situation. NO responsibility can or will be taken. And yes, I am a licensed plumber with my own business in Brisbane Australia
