How to find a plastered hole?

Question

I have a small issue. Few months ago my apartment got renovated, and I listed all holes in walls i want to keep for future use. The rest was, depending on depth, filled with concrete or plastered. And it was done really good, I can't see these spots with my bare eyes.

Now, I forgot to list one hole, so it was plastered clean. But I need to have a hook there, and I'm reluctant to create brand new holes. I would really prefer to use existing one - I need bigger diameter now, so I can afford to be a tiny bit off, but boring new hole would needlessly affect concrete, and if it happened to be just next to original one, it would also be weak. So one way or another, I need to find old one, be it to reuse it or avoid it. But how?

Answer 1

The slightest imperfections can be found on a wall with a bright light, usually brighter than a flashlight, although flashlights have been used before. It may work for you since you may have an idea where the spot is to begin with.

The trick is to shine the light across the wall, hold the flashlight or light against the wall so the light passes over the wall with as low of an angle as possible. The flashlight or light is almost parallel as possible. This way the texture of the wall is more prominent, because every high spot, even the tiniest, casts a shadow. Since the repair has been made recently and has less coats of paint over it, the texture over the repair will be slightly different than the wall surrounding the repair that has more paint on it.