I had my shower demolished and redone in 2023. It was hot-mopped and a cast iron shower drain was used. Then tile work was done. The contractor originally grouted in the shower drain and I told him I needed to be able to remove the shower drain cover from time to time so he then cut the grout along the perimeter so the shower drain cover could be removed when needed. I then discovered that he had not actually fully filled in the four corners (see photo). He said I should not be concerned about the four corners not being filled in because the water goes to the Hotmop which has weep holes for drainage below the tile line. With that, I happily started using the shower. About 2 years later, I wanted to clear out the hair/gunk from the inside of the shower drain so I finally removed the shower drain cover for the first time since I started using it. I was surprised to see standing water in the four corners. Using a toothpick to poke into the four corners, the toothpick encounters a black gummy substance (maybe tar?) and using this toothpick, it appears the height of this water is about 2cm above this bottom black gummy layer. When I poured water into one of the four corners, black substances came out the other three corners. I eventually used a shower hose to spray down each corner to jet out whatever black substances there were in there.
Questions:
1) Is it a problem that even after sitting overnight the standing water in the four corners remains unchanged? I was under the impression that the cast iron shower drain has weep holes which should funnel this standing water away. Does the fact that the water does not drain away even after 24 hours mean that the shower drain's weep holes are fully clogged? What implications does that have for my shower? The water is about 2cm in height above the "bottom" black gummy layer and reaches to just below the metal cup of the drain bowl.
2) What should I do going forward? Should I dry out the four corners and fill it with grout? Should I apply silicone aroud the four edges of the shower drain? Should I do nothing?
Thank you!
