I was replacing an external wall sconce, and noticed that this octagonal junction box doesn't seem to be affixed to the brick wall around it. There's no visible nails, screws, mortar, etc. around it.

It can wiggle a tiny bit, but interestingly, it's actually really stuck in there, and I have no idea how. I can see some metal protrusions around the box that press up against the brick but that ... doesn't seem legit.

I have 3 questions about this:

  1. From a code perspective... is this legit? (Ontario, Canada, btw.) If not, what would be a proper way to secure it?
  2. What would be an appropriate material to seal these large openings around the box? It seems too large for silicone alone. Perhaps a tube of "mortar repair" compound?
  3. I can see past the box and into the wall cavity behind it, and I don't see any insulation. This is an external wall (obviously), shouldn't it be insulated? Could it be insulated without opening the wall and needing to redo the drywall inside (with some spray foam or something like that)?

Some metal bracket sticking out the right side of the junction box, which pushes up against the brick. An image of the wall-mounted junction box, showing that it's flush with the brick.

BTW I temporarily undid that ground wire, I know it needs to be screwed to the box :)

  • Are there metal tabs on the back of the box, or attached by the strain-relief, holding it in place? Jul 9, 2023 at 8:41
  • I imagine the proper way would be to drill the brick for some screw anchors and screw the sides of the box to the brick. But I'd probably just use some poly sealant between the (cleaned) brick and box.
    – Huesmann
    Jul 9, 2023 at 12:03

1 Answer 1


There are definitely some tabs in the back of the box that are securing it to the brick. The screw holes at 12,3,4,6,&10 o'clock appear to have some sort of rivet attachemnts to the tabs. If the box is secure, it's OK.

I'd get some mortar to seal in the box. It will secure the box even more. Where the openings are real small, use some silicone caulk. Adding insulation at this point would be a big job. There's a possibility just that one area lacks it because of the box and sealing around the box will help. Make sure the sconce fits tight up against the wall and caulk it after installation.

In the U.S., that NB cable would be a problem because it's not rated for outdoor use and since it does exit the exterior wall, it would need to be but that's getting real picky.

  • 1
    My understanding is that while technically NB can't go outside at all, many jurisdictions and/or inspectors allow it as long as the box is against or (as in this case) in the wall and the wire is not exposed outside the box. Jul 9, 2023 at 13:55
  • 1
    @manassehkatz-Moving2Codidact That's why the term "real picky" was used but you're right. :-)
    – JACK
    Jul 9, 2023 at 14:01
  • @JACK Interesting, I'm curious to picture it, do you have any images/links showing what the back of this box looks like? I went ahead and sealed the bigger openings with some mortar, then I'll caulk both the smaller openings, and around the light fixture itself. Follow-up question: should I also caulk all the smaller holes in the box (like the unpopulated screw holes)?
    – Alexander
    Jul 10, 2023 at 14:40

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