Spray foam around electrical box?


  #1  
Old 09-27-19, 02:58 PM
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Spray foam around electrical box?

Hi,

Hopefully this is a simple question. I replaced a metal electrical box with a plastic one, but there's quite a gap around the new box. I was going to spackle around it to fill the gap, but I think the gaps might be too big for spackle. On the other hand, I can go around to the back of the outlet from the garage side and use spray foam from that side to fill the gaps, and then just use an oversized outlet cover to cover the "ugly" on the room side. Attached are some pictures. I guess my question is (1) is this just crazy?, and (2) does spray foam and "electrical" not mix (although I'm not foaming inside the box, but around the outside).

Thanks!

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Last edited by PJmax; 09-27-19 at 04:58 PM. Reason: resized pictures
  #2  
Old 09-27-19, 03:21 PM
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IF this is an inside wall just use an oversize face plate. no need to fill in the gaps. If you're getting cold air from the garage use one of those insulating foam pads made for outlets.

But to answer your question, yes you can foam it but I would not. I would rather used blanket insulation.
 
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Old 09-27-19, 04:58 PM
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You could tape the back off and use spackle too.
 
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Old 09-27-19, 05:34 PM
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The code require the gap around the box to be no more than 1/8". Use 5 or 20 minute compound to fix the gap.
 
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Old 09-27-19, 06:14 PM
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You said it was a garage wall. I would foam it. You want an air seal to keep fumes out of the house.
 
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Old 09-27-19, 10:04 PM
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Thanks for all of the replies guys. I think my picture from the garage side (the backside of the box) was a little misleading. The garage is in-fact sheetrocked and I had cut a hole in the sheetrock to get to the box. So I do plan on putting that sheetrock back. Thereís definitely going to be a draft from the garage to this room (and I completely forgot about the fumes), so Iíll probably do a little bit of everything.
 
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Old 09-28-19, 11:00 AM
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I see from the pictures you provided you have the old cloth covered NM cable powering the grounding receptacle. I don't recall seeing much of that old stuff that ever had a ground wire in it, it mostly was all without ground. If you have no ground wire that receptacle should be GFCI protected or changed to a 2 wire receptacle.
 
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Old 09-28-19, 11:28 AM
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That asphalt NM, when it has a ground wire, is usually 16awg, in my experience.

Iíd consider fibertape under any drywall mud. Or even fireblock caulk instead of brittle mud.
 
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Old 09-28-19, 11:56 AM
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There are three cables coming into that box. Each cable has three wires: black, white, and bare copper. In the previous set up, the box was metal. So all of the grounding wires were wire-nutted together ( including one wire from the grounding screw on the outlet), then a pigtail came out to a metal clip on the metal box. Since the new box is plastic, I just put all of the grounding wires together in one wire nut, and then had a pigtail come out to the green screw on the outlet. Hope thatís correct?
 
  #10  
Old 09-28-19, 12:45 PM
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It's not that old. It was common around here until at least the 70s. I have it in my house built in 1958 and it has ground wires.
 
  #11  
Old 10-20-20, 03:29 PM
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Sorry to dredge up an old topic, but I exceeded my amount of wait time before other folks in the house start telling me to finish up the job lol. I was using clear caulk for another job in the house, and the caulk was older and not dispensing well. So I cut it open and decided to cover the gaps on the back of the outlet box (the side that faces the garage) with some of this silicone/caulk. Overall it may not be the most effective solution, I just want to make sure itís not unsafe. Any reason that you could think of where this is considered unsafe? And keep in mind, Iím replacing the piece of sheetrock back into its spot, so it wonít remain uncovered.





 
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Old 10-20-20, 03:57 PM
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We need a few more pictures.

The silicone is fine. You just created extra work opening the wall up.
Spray foam would have been ok too.
 
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Old 10-20-20, 05:18 PM
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In the future, save yourself the hassle of opening up the wall for this. Setting type joint compound ("hot mud") could fill that gap and you could use regular outlet plate to cover. Or spray foam from the front and use the oversized ("I goofed") outlet plate.
 
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Old 10-20-20, 05:26 PM
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For that application you would squirt the foam in around the box. After the foam set (hardened) you would carve out a groove between the box and the wall. Then fill that groove with plaster or spackle.
 
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Old 10-20-20, 07:18 PM
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Thanks for the additional replies. Just for clarification, I didnít open up the wall from the other side simply to caulk/silicone the box. I opened it up because the previous box was metal and was awful. I wasnít able to remove the old box and redo the wiring, so I cut the hole on the opposite side to allow me to get to the box easier.
 
 

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