@pe2dave
If you have a multi tool, how about something like this:
View attachment 152612
I was using similar the other day to cut out a recess for a double gang back box and cable run, in plaster/red brick.
I had two back boxes to fit: the first one I used the angle grinder, while precariously holding my vac nozzle in the other hand, but the airborne dust was unacceptable.
For the second back box, I used the multi tool, and it created hardly any dust without using a vac. I could also control the depth of the cut much more accurately too!
If it’s lime mortar you are raking out, then a multi tool would whizz through the job. Also the fact that it doesn’t need a guard allows a good view of the area you’re fouling.
I have both a 18V Milwaukee multi tool, which purrs like a ginger cat, and I have a corded cheap and cheerful one that would probably make the tips of your fingers go numb after 15mins of use, similar to a <£50 angle grinder. However since getting a High Output battery I will always reach for the cordless.