Is it useful to do waterproofing in some places where the balcony floor is a little hollow?

It should be checked. It is normal for geothermal ground to have cracks.

There is a two-centimeter hollow drum on the floor of the rough bathroom that needs to be repaired. When you see something wrong when decorating, you must repair it well to avoid problems in the process of future use.

According to my experience in decoration, as long as you don't touch it, you can't fall off, if it's convenient, it's better to change it!

Generally, some building balconies and indoor steel bars are not an integrated structure, and cracks on the side of the balcony are very common problems, especially in the eighties, the national building balconies are scattered and numerous, almost every community has been, so everyone is not surprised, but now the commercial houses are generally poured in one piece, and the steel bars are also integrated, so there should be no cracks, which is a quality problem.

It should be cracking, not structural cracking, and structural cracking will not be as big as bending in the middle.