[rnln]

Wow, too many questions and suggestions. Thanks. Let me go through one by one.

This is a slab on first floor bathroom. At the wet/dark area, there was a bathroom sink. The water pipe and drain pipe were leaking above the ground level. The sink and counter were removed. The leaked pipes were fixed 4 years ago.

The whole bathroom floor has vinyl tiles. When I lift the vinyl tiles, there was black mastic type of glue that sticks the tiles to the floor. I scrape it off before grinding the concrete with diamond wheels and I did spray water while grinding to avoid dust blowing everywhere.

trekkor,
I wish I can find a way to find if there is a broken pipe in this area without cuting the concrete.

GWN7,
Do you say Thermal Imaging Camera will identify there is piping under ground, or it'll tell you if there is a leak?

Bugsinrugs,
I wonder if installing the orange membrane from Schluter Kerdi on the floor does this trick?

URY914, Porsche-O-Phile, Look171,
yes the black mastic as I described above. What are you guys saying? Am I using the wrong term? What I meant was the some kinds of glues in black color they used to stick the vinyl tile to the slab. I scraped it off with a scraper tool before grinding the concrete. Please expand your thought.
Thanks.

sammyg2,
If it is $200 to identify the leak spot under ground, it's great. Do you have contact number or any kind of phrase to search on?

trekkor, rusnak,
the other side of the wall in the pic is another room. It has laminate wood floor installed sevferal years ago. No problem right now. The laminate we ripped off didn't have problem that I could see neither .

Another wall is to the patio, there is no water nor rain to get to this wall.

The white sutff was brought to the lab testing for mold and it is not mold. Also, couple days later now, it seem to dry off itself a little more. So, I feel it is drying off very slow. If there is water leak to this concrete slab, shouldn't it be wet forever, and will not be dryed off at all? If there is not a leak, why it takes that long to dry? Are there different kinds of concrete which take longer to dry compare to other kinds of concrete?