sinking back boxes into walls - gone too deep

[imanc]

I'm trying to fit 4 25mm back boxes into walls. I've pepper potted the area with the drill then used a cold chisel to clear out the plaster and brick. However, the result is not smooth. There's a lumpy mess and some cracked brick that is stil somewhat firm, and the back box doesn't seat right. With one recess the back box is about 5mm too deep.

I'm wondering if I can build up the chase with some polyfilla or something to make it straight and the right depth before fitting the back box?

I know that an SDS drill with correct chiselling attachment would do a much neater job, but I don't have one to hand.

I've got 3 more holes to chisel out so any advice would be appreciated!

Cheers, imanc

[newshound]

Polyfilla or even plaster will be fine. Ideally you should still have two fixing screws into wallplugs, but with suitable filler you can get away with one or even none. Finish plaster is slightly less good because of shrinkage.

The other trick if you have two good screw fixings is to pack behind the box with suitable slivers of wood so that the box is square when screwed down.

[Tim Watts]

On Monday 13 May 2013 19:25 imanc wrote in uk.d-i-y:

To a fixed depth? I wrapped tape around my drill as a depth marker when doing this.

I had the same problem on the odd occasion - when too enthusiastic with the SDS or the bricks were a bit crap. Mix a bit of 4:1 mortar and lob it in the back of the hole. Bed the box in to this. If you add a bit around the side you can not bother with the fixing screw(s).

[John Rumm]

I keep an old bag of bonding plaster for such occasions... slap it in, it goes off quick.

[Dave Liquorice]

Get one fixing ready, lob in some stiffly mixed old plaster, push in box and use fixing. position and leave.

Is that a problem? You can get longer accessory screws if the ones you have are too short.

I'd not pepper pot, just closely drill around the edge to a consistent depth. It's easier to cut big bits out of a solid mass rather than one full of holes.

[Frank Erskine]

Use a deeper back box!

[Dave Plowman (News)]

Quick set cement.

[The Natural Philosopher]

car body filler, then replaster. with luck no screws needed. :-)

[Bert Coules]

I've no idea if this in an approved method (and rather suspect that it isn't) but I've mounted several sets of backboxes-in-a-row by first screwing them to a wooden backplate and then putting the whole assembly into a slightly oversized hole partially pre-filled with plaster/cement/mortar/what have you.

The beauty of this approach is that it ensures that the boxes, and therefore the front plates, are all perfectly in line and evenly spaced - something I could never achieve when I used to do it one box at a time.

[Windmill]

I've had better results with an SDS chisel than when I tried drilling then hand chiselling, but still not perfect. However with a metal back box it's sometimes possible to put a large metal repair washer (or 2) behind one of the box mounting holes. Quick and easy, if not ideal.

[Windmill]

Or do as some professionals (?) have done and just take care not to attach the socket too tightly (which might crack it).

[Bill Wright]

You can set the boxes in gunnanail or nomorenails. Bend the unused knock-outs in slightly so there's a key for the adhesive. No need for screws.

Bill

[harry]

Tap all the knockouts in the box in very slightly and set the box in the hole with cement. Leave the knockout(s) you want to use clear of cement. Make sure the threaded holes for your switch/socket are clear of cement.

[Brian Gaff]

Yeah you can use all sorts of stuff for this. Once when younger and still sighted I just bunged in some filler, then the box, levelled it up and held it in the right spot with tape till filler dried, took it apart and drilled the holes for the plugs. Its still up. I guess its like, what the eye does not see....

Brian

[stuart noble]

Industry standard IME. I guess that's why our electrical wholesaler has it stacked by the front door.

[ARW]

Do you want a job?

The only difference is that I mount the wooden board to the wall and then fit the back boxes.

[ARW]

Having the back box set 3mm behind the plaster finish is the correct way to install back boxes for use with flat plate switches and sockets.

[ARW]

Bloody good stuff that out of date bonding.

[zaax]

Yeah or pack it with a piece of wood or what ever you have lying around. I've used old lino tiles before from my box of shims.

[Larry]

Clever, best suggestion yet 👍