I have cut out two holes for 4", metal electrical boxes to be set in to the exterior walls of an old block and stucco garage. I need to secure the boxes by setting them in either concrete or mortar, but am unsure what type of product to use. Would a plain old Quikrete - their basic concrete mix - work for this? Or should I use some kind of mortar mix? I was about to use the common Quikrete simply because I already have some, but then noticed on the package that it said it should be applied a minimum of 2" thick. I don't have that kind of space around the boxes, so I thought maybe that was the wrong product for the project. I also happen to have some old thinset for tiling. May be past its prime, but might work for this? Of course, I'm not opposed to buying whatever the right thing is if neither of these are it.

Any help would be appreciated.

2 Answers 2


they make specific boxes for masonry. these are sealed a bit better than a typically 4 inch square. you can get these in single gang, up to almost anything multi gang or gangable (single gang that join to other single gang to make what you need) You must use rated wire or conduit with compression connectors for this application as well.

  • Can you explain "must use rated wire?" I have 12-2 NM, is that not sufficient? Someone on a forum awhile back told me that it was fine to use that going through the concrete block without conduit. Is that not correct? Commented Oct 20, 2014 at 14:43
  • This will depend on your area, but I believe that unless you have cable rated for a masonry space, you should have your wire in conduit. The internal spaces of a cinder-block wall can be rough enough to strip insulation when pulling. I would be concerned about a pull shredding insulation on a project like this. Commented May 13, 2015 at 15:38
  • This 'answer' doesn't answer the question about what material to use around the box. If the answerer intended to say "don't use mortar or cement", it should say as much. As it stands, it should be a comment.
    – David J.
    Commented Feb 7, 2023 at 21:24

Any holes in stucco should be patched with Portland cement plaster (stucco). An exterior electrical box should somehow be fastened mechanically to the structure (bolts, cement screws). Once pipe fitted and fastened, filling the gap around the box should become obvious; small enough for caulk, or needing patch. If the hole is large\uneven and you do have to 'bed' the box, attach a few bolts sticking out the back to provide as an anchor, or come back later and sink a few cement screws.

I've never worked with stucco but I'm pretty sure it's... cement.

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