We have tenants that have carved holes on the drywall to access the heat pipes and AC mains. At some point they will patch the drywall very well. Perhaps by another piece of drywall that closely fits the hole and all that had to be done is paint it over and it will be as if nothing had been tampered.

So I need a way to detect any discontinuity on the drywall piece (sort of like a stud finder) if such a technique exists.

Of course, I can simply find where the AC mains and heat pipes run through and then sand the wall right in front of them and viola, I've found the patch. But, I was wondering if such a technique exists.

  • 2
    Remember that drywall is put up in sheets anyway; there's little difference between joining one sheet to another, and joining a patch to the existing drywall. Jan 4, 2017 at 6:23
  • Do a wall moisture investigation for health related fungus inspection of all the units before the hole is patched up. I must say you have some rather specific suspicions of your tennants activities though. It almost looks like you plan to be the one doing the patching and are hoping for advice on how to do it well :-)
    – KalleMP
    Jan 4, 2017 at 7:12
  • Any way you can check on the property randomly while tenant occupied? If so, an unnanounced inspection is far more likely to catch these issues. Jan 4, 2017 at 17:07

3 Answers 3


You can try a magnet. They will have to secure any substantial patch with a nail or screw. But really there is no exact way to know what was the patch and what was existing drywall, because the existing drywall will also have screws/nails around it.

So either the patching will be in a unique shape and you can find it or it isn't and you need to take pictures of the wall before they patch.

Real world I seriously doubt this will be patched absolutely perfect. Not only would they have to do a superb job with the drywall and mud but they would also have to prime it and paint it feathered in with the existing area. So in reality a high powered light and a good angle on the wall and you shouldn't have a problem.

  • Yeah, fresh paint always looks different to old paint. Unless they re-paint the whole room, which seems like it would be excessive. Jan 4, 2017 at 6:22

A capacitive stud finder might work, particularly if the patch is fresh (containing more moisture).

You might also locate it by gently tapping the wall and looking for a square area (rather than a linear stud) where it sounds different.


In addition to the bright light angled at the wall to detect changes in the spackle and/or paint, another less desirable but more certain option is to use an inspection camera. This however requires drilling a 3/4 hole, (easy to patch) inserting the camera wand into the wall and looking around for obvious patching from the inside or even the other side of the wall. Sometimes you can snake the camera wand through the space adjacent to an outlet or switch box, vent etc. A moisture meter might detect a real recent patch.

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