Deepen backboxes in block wall?

[Andehh]

So I've fallen in love with cheap smart switches. They're cheap, smart and effective!

 

The only issue is they need 20mm extra depth then existing backboxes have.

 

The current backboxes are well plastered in, and the cables are tightly routed in.

 

Any recommendations on how to best cut through the metal backbox, and then chisel out the block behind it in a reasonable fashion?

 

 Thanks

[jfb]

Tricky to do without affecting the plaster but I have managed to do it by cutting around where the box meets the plaster and then unscrewing the box. I think if it doesn’t come out easily I had to tap the edges of the box in with a chisel enough to get pliers to pull them out. But careful for the corners damaging the plaster on the way out!

[Andehh]

I've found you can buy multi cutter blades for metal, and for masonary.

 

Is there any reason why I couldn't use these to carve it all out in situ?

[FuerteStu]

1 hour ago, Andehh said:

I've found you can buy multi cutter blades for metal, and for masonary.

 

Is there any reason why I couldn't use these to carve it all out in situ?

The box will be fixed at the back. Cutting out the back will likely make a real mess with a multi tool, as with nothing fixing the box, it will shake free of the plaster and fall to pieces

 

 

[Nickfromwales]

Collapse the boxes in on themselves, leaving the panel with the cables until last. 
 

Remove, chase, fit new box.
 

Will require patience and some understanding that every action has an opposite and equal reaction, eg if you fold the centre of the panel in the edges will contort outwards slightly, firstly, and THEN fold in.

 

If you damage the edges of the plasterboard during these alterations then be sure to inject some 330 foam behind the boards and around the box, as this will give you something solid to fill / sand / paint vs ‘flappy edges’. Wet the block work and plasterboard edges with 50/50 PVA/water mix immediately prior to foaming up.