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Posted: 10/6/2012 7:41:39 PM EDT

gents,

i would like to mount an outdoor (weatherproof) box on an irregular stone wall surface; subsequently an outdoor floor light/motion sensor will be mounted to the box.  the surface that the box is going to be mounted to has stonework applique mortared over lath, then grouted, and hence the surface is not flat.  the stones are nominally about 3/4" thick.  electrical wiring would exit the box at the rear, penetrating the wall directly behind the box.

what's the best/right way to do this?  i was thinking about building up an area with some mortar so that it was in fact flat, then mounting the box to it.  i was also thinking that i could simply use NM or IMT conduit w/threaded fittings and not securing the box at all –– the conduit would hold it in place.  that doesn't seem like a good idea however.

picture below is old, but the new light would go on the surface between and above the garage doors.  btw my garage is not that messy now...

ar-jedi



Link Posted: 10/7/2012 5:13:57 AM EDT
Is there a way to sink the box in the stone and use longer box screws to mount the fixture?  That way you can shim and grout around the fixture and not have an exposed box sticking out of the wall.
Link Posted: 10/7/2012 7:13:49 AM EDT
Quoted:
Is there a way to sink the box in the stone and use longer box screws to mount the fixture?  That way you can shim and grout around the fixture and not have an exposed box sticking out of the wall.


This. Use a 4" grinder/ cold chisel to recess the box
Link Posted: 10/7/2012 7:28:09 AM EDT
I would do what was suggested above.

BUT, if you don't want to go that way: I would get threaded rod and through-bolt the box to the wall. Instead of using mortar to make a flat surface go to home depot and pick up this stuff called duct-seal. Its black, sort of like silly putty or something like that. Its the stuff used to fill gaps in weatherheads and conduits etc. pile a bunch around the back of the box and when your tightening up the bolts it will fill any gaps and start squeezing out the side, then you can just cut away the excess. It has a light insulation value and will keep bugs and water out. Its also cheap and has many, many other uses.

Goodluck Jedi!
Link Posted: 10/7/2012 7:29:25 AM EDT
Two thoughts:

1. Find an easier place to mount the light, like on a soffit above, pole, etc.

2. Rent a core drill rig and core drill a hole to fit a standard round box through the stone face and mount the box to the structure behind with the box face flush with the front of the stone face.
Link Posted: 10/7/2012 8:29:26 AM EDT
My first thought would be similar to one of the above.

I'd mount the box using 3 or 4 points of attachment. Mount it against the 'highest' point with a conduit going back in to the wall. Once the box is mounted and perpendicular to the ground you backfill with grout. If the offset discrepancy is too large you might consider shimming it with some flat stones similar to the facade and letting these show through along the edges to keep it aesthetically pleasing.
Link Posted: 10/7/2012 9:19:23 AM EDT
Install a piece of unistrut then set your bolts from the back side.   Screw chisel and grind.  Way too much work.
Link Posted: 10/7/2012 10:26:06 AM EDT
If it is to be on the wall, I would grind and recess it, filling the gaps with mortar.
Link Posted: 10/7/2012 10:52:11 AM EDT
If you can arrange so that the box 'aligns' with a piece of stone you can remove the mortar and ten crack off the section to make the hole to recess the box.

Plugging chisel, carbide drill bit just under the joint width.

Drill at last the four corners, clear between three of them, break of stone section.

Do not assume the box must be round, or that a rectangular box cannot be installed horizontally (as opposed to vertically).
Link Posted: 10/7/2012 12:31:38 PM EDT
In your case of  spotlights and a motion sensor....if you decide to go the workbox route, recessed or surface. You probably want to mount the box only in the vertical position because of a cover plate's threaded KO orientation.




ETA...My vote is for a recessed vertically mounted masonry box (keeps the threaded screw hole channels inside the box).

...and two to four OWC's (they are add-ons that expand between the box and recessed sides of the opening, these will hold the box in place while you sludge in mortar plus they will help tie the box into the mortar.
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