Fixing a metal flush-mount electrical box in a messy hole in a brick wall

[Adam Funk]

I decided to fix a loose surface-mounted double socket behind the sofa this morning (loose because someone before me didn't screw it to the wall very well) & decided to go whole-hog & replace it with a flush-mounted one. (What the heck, I have this hammer-drill that does hammer-only, & some chisel bits I haven't got much use out of yet, I thought.)

Unfortunately, every other time I blasted a little bit out to get the box to fit, a chunk of brick out of the middle fell out. The spot also has 1 horizontal & 1 vertical mortar joint in it. I ended up with a hole that the box fits more or less right around the edges, with a gap behind the box in the middle, & one very long screw in the middle of the box going through to a plastic plug in the brick. The box & socket are not quite square & perfectly surface-mounted, so I plan to go back again & even everything out. I am thinking of using a deeper box & chipping out the corners (but not the middle) more.

What are some good ways to fill in, even out, or otherwise deal with a messy hole like this to take an electrical box neatly? (The outline of the hole is fairly rectangular; it's the depth that varies messily.) I'd prefer methods that don't take more than a few hours to dry or set (because of the other appliances on this circuit).

Thanks.

[Mike Tomlinson]

In article , Adam Funk writes

Butter the back of the box with 10-minute quick-setting cement, varying the thickness to suit the messy back of the rebate. Tap the edges with a hammer to get it flush with the plaster. Put the fixing screw(s) in but don't tighten too much. Insulate the wires with a choc block so you can put the power back on, then switch off and refit the socket tomorrow when you can be sure the cement has gone off.

[Andrew Gabriel]

Bonding coat plaster. Paint the brickwork hole with dilued PVA if you have any, or water if not, and let it soak in. Fill the hole with plaster and push the back box into it (with the cables already routed into the box through a gromit). Make sure the plaster is in contact with the rear and outsides of the back box. Try to keep the plaster out of the fixing holes and make sure the sliding leveling hole still slides OK. Small amounts which ooze through the fixing holes in the back box are a good thing. Leave to set for 4 hours, but I would suggest not fully tightening the socket mounting screws for 24 hours. It will be stronger than if you'd screwed it to the brickwork. Always a good solution where you have spalling (crumbly) bricks.

For finishing, you can either polish off the plaster flush with the wall (bonding coat is not really the right plaster for that, but it can be done), or use a scraper to take it a couple of mm back from the wall surface, and use finish coat plaster or polyfilla or whatever you normaly use to make the finish surface, or leave the bonding coat just proud enough to sand down when set and dry.

[ARW]

Out of date bonding is better than new bonding for this job:-)

[spuorgelgoog]

I like a bit of squirty foam behind the box, because it expands it pushes the box outward against its fixing screw(s)

With non-expanding filler I find it too easy to push the box too far in, and then it doesn't sit nicely if I try and pull it out again.

I also think the foam adds insulation to make up for when I go through to the cavity ;-(

Once you've got the box in choc-block the cables together and you can leave it to set after putting the lecky back on (*not if you have children or animals who like to play with exposed live wires*)

Owain

[John Rumm]

Indeed, I keep a geriatric bag in my workshop just for this kind of application...

[Mike Tomlinson]

En el artículo , ARW escribió:

Sets bloody quick (as I found out!)

[jgh]

I lost three trowels firmly welded into bucket of bonding that I turned my back on for half a second.

JGH

[Adam Funk]

That sounds good, thanks.

[Adam Funk]

...

I don't have any of that, but since it comes in 25 kg bags, I'll have plenty of old stuff for the next one.