Shower tub conundrum!? My shower walls were moldy because they used regular drywall instead of...

My shower walls were moldy because they used regular drywall instead of concerte board, so I ripped the tile walls out down to the studs so I could go back over them.

But I now see that the concrete floor does NOT stir right to the studs. It has a 1/2 inch "trench" adjectives around it between it and the wall studs. The waterproof membrane contained by the floor does go underneath this trench and is flush against the studs.

1] If have no perception why they did this trench. They did have the drywall lay down inside this trench (which I understand is wrong and is probably why it get so wet - the board astern the tile should be slightly raised from the floor). But what is beside the trench - why did they do it this way?

2] I'm not sure what to do in the region of it. I will be installing concrete board on the walls now. Someone said I should crowd this trench with a bonded topping type product to attain rid of it. Otherwise I'll just depart it as an "air pocket". I'm not sure what to do!???

Thanks!
Trying plastering for the first time and involve...
Answers:    What's next to the tile fetish, put a fiberglass unit within and fuhgedabodit.
I am moving overwelming Ideas to dectorate my...
If they had the drywall lay down into the trench then you should know how to have the cement board lay down into the trench as well. The cement board will be untouched by water and should saturate the trench quite other. Just make sure you hold at least a 3-mil plastic vapor barricade behind it.