Patress/back box depth

[gap]

I'm planning to plaster an interior block wall in my garage. At the same time I hope to replace the surface-mount light switches with standard flush ones and bury the wiring in the plaster (protected by metal conduit). If I go by the plaster manufacturer's recommended thickness, that will be about 11mm bond coat followed by 2 or 3mm multifinish. Typical back boxes start from around 25mm depth, so if I mount the back box onto the block surface, it will be >10mm proud of the finished wall.
I must be missing something! What is the correct way to do this? Am I supposed to chop the back boxes into the block wall to get the desired depth? Seems like a lot of work for what must be a common thing to have to do.

Thank-you very much!

 

[Tigercubrider]

Chip out some brickwork

 

[gap]

I see, thanks Tigercubrider. I was worried you'd say that! I might need to fork out for an appropriate tool unless I can manage it with a hammer and chissel.

 

[Tigercubrider]

Drilling loads of holes to a set depth helps

YouTube is your friend

 

[foxhole]

Back box for light switch usually 16 mm

 

[gap]

Good to know about the 16mm back boxes for light switches. Doesn't sound like I'll need to dig too deep then. Thanks as always!

 

[Happyplumber]

You want to chop the backbones into the brick work
SDS drill with chisel bit is your best friend for this project
35mm as well as 25 metal back boxes are available ,personally I usually buy deeper ones in case you have some with inbuilt USB and then you have plenty of room in the box

 

[flameport]

Good to know about the 16mm back boxes for light switches.

Beware - those things are only suitable for normal switches. If you or someone else then wants a dimmer or a flat plate design, it will not fit.