I have these black lines in the join areas of my wall tiles from my shower: enter image description here enter image description here

They are both in the lower part, where the wall meets the floor. I have similar lines near the drain: enter image description here

I have tried to fix them using both an anti-mold and an anti-rust solution, but neither worked.

I should also mention that I don't have a window in the bathroom, so humidity might play a role here.

What are these black lines? How can I fix them?

  • 2
    Certainly not rust. Is your "anti-mold" solution designed to clean existing mold or prevent mold growth? It's likely that some bleach and a scrub brush (wear gloves, old clothes and eye protection) will clean that right off. With no window, do you have a vent fan? If so, does it get used?
    – FreeMan
    Commented Jan 28, 2022 at 19:30
  • Thank you! After scrubbing for what seemed like forever, I managed to clean up most of it with bleach and with the help of a needle. Based on the packaging, the anti-mold solution is designed for cleaning mold, but it did not help me at all. The bathroom has a vent fan and I am using it, but looks like I should probably use it more. Commented Jan 28, 2022 at 20:51

1 Answer 1


Use a diluted solution of bleach to scrub the mold off of the caulk. Since bleach can be dangerous, be sure to wear old clothes, rubber gloves and eye protection!

Once you've got it cleaned up, use your bathroom vent fan and let it run until the humidity in the bathroom matches the humidity in the rest of the house.

It would be a good idea to run the fan while you're scrubbing with bleach to help get the fumes out of the room, too, since bleach has rather a nasty smell.

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