In the past I've used the angle grinder to chase out electrical back
boxes and have created an amazing amount of dust.

Today I tried a new method (for me)
I purchased a couple of these for my multi-tool

https://www.saxtonblades.co.uk/fein-...-end-cut-blade

https://tinyurl.com/yypkfmba

and on the slowest speed cut the outline for two double 35mm back boxes
and the channel for the wiring. This was into soft brick overlaid with
10mm of old fashioned (horse hair) plaster. A few bricks were more like
cinder and were harder. While it did create some dust and a mask is
advisable most of the dust just dropped to the ground rather than
becoming mainly airborne. If doing the same again I may consider a spray
of water to further contain any dust.

I also used the multi-tool to cut diagonal slots in the "waste" area of
the back boxes. The material to be removed came out fairly easily with
the use of a scutch chisel and lump hammer leaving very clean edges and
corners.

https://www.toolstation.com/draper-scutch-chisel/p18718

Cutting the back box outline to a depth of 35mm+ probably took 10x
longer than with a angle grinder but possibly saved 10x the time
cleaning up the dust afterwards.

The blade does show signs of damage but probably could manage the same
again before discarding.

On tip is to often move the blade out of the work to clear the debris.

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