Ok, I come from the US, where most interior walls are drywall. To hang a picture, you simply bang a nail in and *voila* -- you're done.
Here in HK however, all the interior walls seem to be made of concrete, which require special 4-nail hangars to hang even a simple picture. That's fine....but when I just tried to pull one of the hangars out, it left a large divot the size of a HK$10 coin.
In the US, I'd simply buy some spackle and paint over the hole. But what does one use to patch a hole in concrete? Spackle? If so, where does one buy that stuff and what is it called here?