I live in a condo that was built in 1980. I've replaced a few switches and outlets around the unit. Every single electrical box is filled with chips of this material, and the wires are coated (either a little or completely) with what I assume is sprayed-on primer that leaked into the boxes.

The material was already at the bottom of every box when I removed the cover plate.

I have limited experience with building materials, but it looks like plaster - it crumbles like chalk under pressure, snaps if broken and dissolves in water.


  1. Is it likely to be plaster, or some kind of fire retardant or insulation that was once in fashion?

  2. Should I clean out the existing electrical boxes? Most haven't been opened since the unit was built.

  3. How did they get there? Is it just laziness on the part of the original electricians?

I know this is a bit vague, let me know what other detail I can add.

chipped material in electrical box

  • 4
    The markings on the wires themselves are definitely from paint. It's most likely that this was rolled and the roller hit the wires. If it was sprayed, they most likely be much more evenly covered. That's not a problem, either, though it can be very annoying if all the wires in the box are now the same color. You should be able to scrape it off with a finger nail it it's extreme enough that you can't tell wire colors any more.
    – FreeMan
    Sep 21, 2021 at 13:53
  • 1
    This case is minor. We often see the wires so coated you cannot tell their native colors! By the by, the ground wiring you see is completely correct. The cable ground wires go to the metal box first, as they should. Ground is then carried to devices either by the mounting screws if permitted, or wires placed on the other ground screw site (which takes a #10-32 screw, any hardware store sells that). Sep 21, 2021 at 17:34
  • @Harper-ReinstateMonica Thanks for that. Even given my limited knowledge of electrical, I haven't found anything worrisome in the actual wiring so far.
    – msanford
    Sep 21, 2021 at 17:47
  • 2
    I recommend cleaning this stuff out when opening up a box to work on it. It has a bad habit of falling out onto the floor as you're working. It's not a fire hazard but breathing in the dust can irritate your lungs and nose, plus you don't want pets or small kids trying to eat it. Pure gypsum isn't poisonous, but drywall adds a lot of additives to it.
    – bta
    Sep 21, 2021 at 22:43

3 Answers 3


Gypsum and joint compound aren't combustible. It's not a problem. Clean it out if it bothers you.

This has nothing to do with laziness. It has to do with efficiency of the process, which often looks like this:

  • Framing carpenters or masons put up the walls
  • Electricians "rough in" the conduit, boxes, and wiring
  • Drywall hangers put up the sheets and tapers and painters finish the walls
  • Flooring installers do their thing
  • Electricians come back and close up their work, adding devices and cover plates

At that point, it's not practical for electricians to carry a vacuum cleaner around with them. Nor is it important, really. They need to shave extra drywall mud from around the boxes--it gets smeared over them when the tapers do their work. It would slow progress down considerably if they had to clean out each of the hundreds or thousands of boxes on a job. No one would be happy with that or the cost it would incur.

  • 3
    Yeah, generally if someone wants to do something about it, it's done by the electrician at the rough-in stage, putting plugs (can be as simple as wadded newspaper) in boxes before the drywall folks come in and then pulling them out when it's device install time Sep 21, 2021 at 23:29

Those are just flakes of drywall compound. They are inert and not flammable. That quantity presents no problem at all.

In the course of working in the boxes, you can clean them out, but I'd never deliberately open a box just to clean it.


It is just a bit of drywall. It does not conduct electricity and is not combustible or flammable. Don't worry about it.

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