How to replace damaged switch box?

[Klaus_K]

Not sure if this counts as electrical work, but I figure this is the best forum to ask this question.

I have a one-way light switch, where the mounting screw was stuck in the screw hole on the box. Removing the screw completely ripped up the plate, so I now only have a screw socket on one side. Ideally, I'd like to remove the old mounting box and replace with a new one.

I'm happy to rip the old box to pieces to prize it out of the wall, but I'm not sure how to put a new one back in its place. The hole in the wall is tight around the box with brickwork and plaster. To make things even worse, there is tiling around the hole, which overhangs the box.

Can anybody suggest a tool(s) for cutting back the tiling by a faction of an inch and enlarging the plastered/brick hole which contains the box. I guess that the tiling cut would need to be pretty clean, since that would be visible, but it doesn't matter if I take back a bit more of the plaster/brick, since that will be hidden by the tiling.

 

[Iggifer]

One option is to buy a 3.5mm rethreader and a 3mm HSS drill bit. Drill a hole in the back of the box where the screw lug would be, then use the 3.5mm tap to thread the hole.

Then get a long 3.5mm socket screw, and voila.

You will need to drill deep enough into the wall through the box to create some clearance, and will likely destroy the end of the drill bit, but this is a nice cheap, mess free option to try first

 

[DetlefSchmitz]

On occasions like this, and when I haven't been pressed by time, I've used a Dremel. Two tools spring to mind, one being a cut-off wheel (make sure you have a good number before you start). The other is a bit (a kind of milling bit) with abrasive edge which can be used to cut unusual shapes out of tiles fairly safely.

But yes, it would be least disruptive to go with the sort of approach Iggifer suggests. If the box is otherwise not too damaged. Araldite and spare parts cut from another box also spring to mind.

 

[SimonH2]

If replacing the box, you also need to allow for the fact that you can't just "plop" the new box in with very little clearance. It needs to be threaded onto the in-place cable, and then the rest of the box "hinged" down into the hole. Thus the clearance in one dimension needs to be a bit more than if you were fitting a new box - eg if the cable enters at the top, the hole needs to be high enough to take the top-front to back-bottom diagonal.
Slightly different if the cable is in conduit and you have access to pull it back.

But as others have suggested, for the situation described, an in-place "fix" would seem a good idea if you can manage it.

 

[Klaus_K]

All good ideas folks. I've actually bought a replacement box already, so I might see if I can cannibalise that by removing the threaded part and either slotting that or glueing that into place in the old box. If memory serves, I think its a bit of shaped metal which just slots into the side of the box. I'll post an update tomorrow

 

[Klaus_K]

Turns out that in the metal box I bought, the screw holes are mounted in a bit of metal that is formed by bending a piece out from the side of the box. So I;ve gone ahead and ordered a rethreader from amazon, plus a pack of screw extenders, so I can stick to using standard length screws. Thanks for all your help - diynot really is the most useful forum I've ever used - I'd never even heard of a rethreading tool until yesterday

 

[Iggifer]

You'll probably never use it again after this one time! Mine doesn't even come out of my toolbag all that often

 

[Klaus_K]

You'll probably never use it again after this one time! Mine doesn't even come out of my toolbag all that often

I've got an awful lot of tools like that When you need it, you really need it.

 

[ban-all-sheds]

I've got one and I've never used it. Ditto a couple of modulo screwdrivers.

And a floor nailer which I will probably never use having discovered Tongue-Tight® screws.

Please don't get me started on the welder which Mrs Sheds insists I'll never need again. And don't tell her about the pyro cable and the tools, pots and glands - I might find an opportunity to use them.

 

[Klaus_K]

Just to complete the tale, it turns out that the back of the mounting box goes straight through to the brickwork, at precisely the point where I'd like to make a screw hole into the box. This is because this part of the box is the part that was bent around to make the original screw hole (that I managed to shear off). So, I'm going to drill into the brickwork and Araldite an extension stud into the wall (https://www.tlc-direct.co.uk/Products/MK3710.html). I can stack these up if one isn't long enough to do the job on its own, but it ought to be easy enough (famous last words ).

 

[securespark]

I take it is isn't a plasterdepth (16mm) box?

 

[Klaus_K]

I take it is isn't a plasterdepth (16mm) box?

Not sure what a 'plasterdepth' box is, unless it's one of those boxes which lock themselves behind a plasterboard wall (e.g. https://www.tlc-direct.co.uk/Products/MTMDLB1.html)? In any case, it's a regular metal box, that is screwed into the brickwork. It looks like breeze block at the back - maybe not the strongest of materials, but probably good enough to take a retaining screw for the switch - if I go deep enough and use enough Araldite.

 

[EFLImpudence]

Use filler.

 

[Gteuk]

You could have glued something like this to the back I.e a big blob of gripfill it would never move then,, Ah well you have done it now so too late

 

[Taylortwocities]

Not sure what a 'plasterdepth' box is

One of these

only 16mm deep (ie as thick as a skim of plaster)