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Back box in dry wall


Blue Fox

Question

Hello all,

been to look at a job job today and whilst there customer comented on a light switch which is coming off the wall. Took it off and no back box, no problem I'll put one in and all sorted, but then realised why there was no back box - the plasterboard walls are too close to fit a dry lining box, there is only a approx 5mm gap between plasterboards and original switch had been screwed into wall but this has caused wall to break up over the years. Anyone got any ideas on this? Was thinking of fitting a 16mm patress box as last option but custmer really wants it set into the wall.

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16 answers to this question

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Wonder which not so bright person came up with straw walls? do they need cavity wall insulation though?!

Generally not because they are internal walls.

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Best way around this is to scrape away any loose wall, and get a deep metal backbox.

Fit it so that its flush with the outside surface of the plasterboard then use foam to "stick" the back box in place. If foam does not do it you will have to use resin, this will set like rock and hold the backbox in place without any screws.

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surface pattress ?

I suggested that but they aren't keen on that want it all flush.

Batty - its almost back to back plasterboard but not quite there is a small 5mm gap

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done a job a while back with a thin wall. turned out to be 2x plasterboards together and skimmed either side. made installing light switch very hard, and the SFCU that was supposed to go there got put on a different wall

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Hello all,

been to look at a job job today and whilst there customer comented on a light switch which is coming off the wall. Took it off and no back box, no problem I'll put one in and all sorted, but then realised why there was no back box - the plasterboard walls are too close to fit a dry lining box, there is only a approx 5mm gap between plasterboards and original switch had been screwed into wall but this has caused wall to break up over the years. Anyone got any ideas on this? Was thinking of fitting a 16mm patress box as last option but custmer really wants it set into the wall.

From this description I would assume its a dot and dab refit.

Its not a wall built from stud and board.

Thats what I assumed and thats the answer I gave for this very situation.

The fact that you mention the original switch and the comment on the original wall crumble, would lead me to think its a dot and dab. If so foam or resin is the only way to go.

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ive seen walls before that are two sheets of plaster board with a sort of corrugated cardboard in the middle, this is maybe what you have here. VERY thin, only about a 10mm gap in between the boards.

This is maybe what you have here.

16mm box and gripfill?

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ive seen walls before that are two sheets of plaster board with a sort of corrugated cardboard in the middle, this is maybe what you have here. VERY thin, only about a 10mm gap in between the boards.

This is maybe what you have here.

16mm box and gripfill?

I agree, if there is a 5mm gap between the two plasterboards then you should have roughly 16-17mm depth if you stick a 16mm metal box on the opposite plasterboard with some No Nails or Gripfill.

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ive seen walls before that are two sheets of plaster board with a sort of corrugated cardboard in the middle, this is maybe what you have here. VERY thin, only about a 10mm gap in between the boards.

This is maybe what you have here.

16mm box and gripfill?

Thats at least 50mm from wall to wall and reinforced with a cardboard web.

Its a right B to get cables through but is a very tough wall constuction.

Howver it would not now conform to building regs for insulation or sound.

The OP would suggest a dot and dab, this is the only explanation for a 10mm gap between surface and wall.

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ive seen walls before that are two sheets of plaster board with a sort of corrugated cardboard in the middle, this is maybe what you have here. VERY thin, only about a 10mm gap in between the boards.

This is maybe what you have here.

16mm box and gripfill?

That's called Paramount wall... loads of houses around here have the stuff upstairs. It has a layer of plasterboard, cardboard and then another layer of plasterboard....it's about 50mm thick in total.

I don't have a problem with running cables in it (especially from above),, you just drill a hole in the wood batten and then smash the cardboard out with some oval..

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I'll also confirm the corrugated cardboard is called a paramount wall. I use stout fence wire to push though it if wiring new.

The OP's wall sounds like what we call 'plasterboard sandwich'. The correct term is 'laminated partition'. Basically a frame of batten is made around the ceiling, wall, & floor, no middle bits like a stud wall, one side is then tacked around the perimeter, then a really thick type of plasterboard is stuck on the inside of the tacked board, they didn't have dry wall adhesive in those days so used thistle plaster instead to stick with. This thick plasterboard is called 'planking'. As it's about an inch thick it's really heavy so it's only about 600mm wide. The wall is finshed off with a top sheet of plasterboard tacked on the remaining surface, but with a few dabs of sticky on the planking as well.

Getting a back box in is tricky, so is converting a single to a double. I use a 25mm wood auger bit to drill out the planking deep enough to get a regular 25mm deep metal box in, a few squirts of gripfill on the back of the metal box holds it in place long enough just about.

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Wonder which not so bright person came up with straw walls? do they need cavity wall insulation though?!

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