Plastic backbox repair

[xiahoudun]

Hi all,

Wanted to replace the faceplate but when I've gone to attach acrew it back in the thread has gone on both sides, can't get any purchase whatsoever.

Most of the advice on repairs I can find online seems to be for metal backboxes but this one is plastic - please see attached picture (most of the backboxes in the house were in this unfortunate state when we bought it).

Not sure if there is enough material left to retap as the hole seems quite wide- is it actually possible to retap a plastic backbox?

Any ideas on how I might be able to fix this without getting the backbox replaced?

Thanks in advance for your advice.

 

[blup]

Replace it with an earthed metal back box.

Blup

 

[DiyNutJob]

Stick a splinter of wood in there so that there is bite for the screw.

 

[oldbutnotdead]

Stick a splinter of wood in there so that there is bite for the screw.

Matchsticks used to be favourite back when everyone smoked- many wobbly door hinges I've shimmed with Rizla packets and plugged the screw holes with Swan Vestas

 

[Wayners]

I'd rip out and replace with metal box stuck in with filler. Something like Toupret standard filler.
When set add a screw although I don't always as won't go anywhere

 

[winston1]

Retap the holes M4.

 

[sparkwright]

Retap the holes M4.

Yes, this might work, particularly as I doubt the holes on that particular plastic box even has a brass threaded section.

However, it is likely the M4 screw will NOT pass through the socket faceplate screw hole though.

It is also likely the M4 screw head will not fit into the screw hole faceplate of the socket.

Another 'bodge' I might do in this:
If the back box is pvc, drill the screw hole with a 5mm drill, insert a yellow wall plug. Thread the yellow wall plug hole with a M3.5 tap a few turns, insert the M3.5 screw.

If the box is not PVC, or it shatters, drill a 5mm hole through into the masonry, insert yellow wall plug, thread a few turns with M3.5 tap, insert longer M3.5 screw.

To clarify, a 'tap' is a re-threading tool, M3.5 screws are 'machine screws'.

 

[Tigercubrider]

Buy another plastic back box and smash it to bits, recover the brass bushes.
Use a soldering iron to push the bush into the plastic and cool.
Or a hot glue gun and push the bush in.

 

[sparkwright]

OR
You used to get those special adapters for fitting in wooden back boxes, to accept a modern light switch.

You cut one of those in half.

TLC had these about 8 years ago, when I needed one for some special project I was undertaking (which didn't involve wooden back boxes I might add).

 

[Adam_151]

Use a soldering iron to push the bush into the plastic and cool.

Arn't these boxes a thermosetting plastic?

 

[JohnW2]

Use a soldering iron to push the bush into the plastic and cool.

That will not work with the urea-formaldehyde material normally used for electrical accessories (which is a thermosetting material).

Kind Regards, John

 

[333rocky333]

You could drill it out a bit and glue in a couple of 3.5 mm nuts
Them boxes often had brass inserts in and they tended to push back too far, sometimes your lucky and can pull them forward enough to reuse, but you may need a long 3.5mm screw to do this, which most people do not have.
As its the wrong box anyway going forward may be best to just break it out and fit the correct metal box, which will fit in the hole as they are smaller than the plastic one.

Chances of 2 lugs gone is slim, you sure the screws are long enough, or maybe its an old box with BA thread

 

[333rocky333]

Yes, this might work, particularly as I doubt the holes on that particular plastic box even has a brass threaded section.

Never known one to have just a plastic thread.
They tended to have a bush pushed in from the rear, often if you crossthread the screw or pushed too hard, you could shear it off and it would push back in too far, as said above sometimes it pulled forward enough to grip again and you could tighten the front enough by keeping pressure on.

 

[sparkwright]

Never known one to have just a plastic thread.
They tended to have a bush pushed in from the rear, often if you crossthread the screw or pushed too hard, you could shear it off and it would push back in too far, as said above sometimes it pulled forward enough to grip again and you could tighten the front enough by keeping pressure on.

I am reasonably sure the pvc flush boxes that were sometimes for plastic conduit systems, around late 60s early 60s didn't always have brass bushes, and frequently failed.

Similarly, the metal shallow depth flush switch boxes often used about 60 years ago had nylon lugs, again prone to failure.

 

[SUNRAY]

Never known one to have just a plastic thread.
They tended to have a bush pushed in from the rear, often if you crossthread the screw or pushed too hard, you could shear it off and it would push back in too far, as said above sometimes it pulled forward enough to grip again and you could tighten the front enough by keeping pressure on.

Threade directly in the 'plastic' was very common for these surfaced mounted patresses for a period of time. The drill out and plastic wall plug is a good possibility for a solution, another is to drill out and fill with a 2 part filler or Polymorph, then when set drill and tap