Back box question

Decker · 13 Nov 2020

In our ensuite we have a dual fuel towel rail and recently the back box cover plate came away from the wall. Upon further inspection the back box is held on as per the diagram below:

A plasterboard fixing (and screw) was holding the back box in place. In addition, the end of the fixing sticks out of the wall in the cupboard. The plasterboard around the fixing has given way so the whole fixing has come away.

I have looked at replacing the box with a dry lining box but as the plasterboard is attached to a piece of chipboard I do not believe the clips to hold the dry lining box in place would close. In addition, the original hole is not that cleanly cut out:

WhatsApp Image 2020-11-13 at 13.24.19.jpeg

Appoligies if this should not be in the electrics thread but does anyone have a suggestion as to how to firmly affix the back box?

Many thanks

EFLImpudence · 13 Nov 2020

I would glue a piece of wood to the rear plasterboard and wait until set. You can use as big a piece of wood as you can get through the hole. Use a grab adhesive like gripfill.

Then get as deep a backbox as the remaining space allows - 35mm. or 47mm. Screw it to the wood.

Then fill the spaces with filler and make a nice square hole.

Decker · 13 Nov 2020

Thanks @EFLImpudence, will try that

Adam_151 · 13 Nov 2020

If the space in the next room is only a cupboard and you have to get the polyfiller out anyway, I'd be tempted as well as putting glue on the wood, that you drive a few decent length plaster board screwsfrom the other side (not so long that they fowl putting the back box on though), also means you can do it all in one go instead of having to wait to glue to dry and hope its 'taken'

sparkwright · 13 Nov 2020

If that really is chipboard (looks like laths from here) then...

Fit a piece of batten to inside of chipboard.

Use two 2 inch screws through the finished plasterboard on the bathroom side, through the chipboard, and into the batten.

So, for instance, there will be one screw at the top of the big hole, one screw at the bottom of the big hole, and the batten will be vertical - bridging the big hole.

Then fix a 25mm deep single metal box to batten. The box should be reasonably flush with the wall.

Taylortwocities · 13 Nov 2020

Metal back boxes have a number of holes in the front edge. It shouldn’t be beyond your capabilities to fit the box in the front of the wall and screwed into the chipboard through the edge holes.

sparkwright · 13 Nov 2020

Taylortwocities said:
Metal back boxes have a number of holes in the front edge. It shouldn’t be beyond your capabilities to fit the box in the front of the wall and screwed into the chipboard through the edge holes.

Good point, though the hole in the wall looks so large it may be a struggle.

Decker · 16 Nov 2020

Thanks for all your suggestions, in the end I glued a piece of wood to the back of the hole, against the plasterboard and when firmly attached also screwed it down from the cupboard site. I then remounted the back box onto the wood and the cover is now in place. I finished the job by replacing the sealant that surrounded the cover.

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Back box question

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