What's That Dark Grout Line In My Shower Floor?

A member of our Facebook group asked the question "Why would only this little grout stay dark/wet?" If you read through the comments the consensus is this thin-set that was not cleaned out before grouting. I believe that's wrong. The dark line is about 1" long and if this had been thin-set it would have been visible instantly after the grout was completed. What's happening is water is under the tile, water is trapped.

So how is the water getting trapped under the grout?

Well at this point I am using my 30+ years experience to diagnose this from a far. The shower drain assembly has a brilliant built in system to allow water that get trapped in the mud base to slowly escape and make it's way down the drain. If you look at the picture below you can see small groves under the drain. These channels allow the water a path, but you have to prevent them from getting blocked. Trust me if your not actively preventing these weeps from getting blocked you can guarantee there clogged. There are a few ways to prevent the weeps from getting blocked but I'm not going to explain how to properly install a shower drain I would refer you to the NTCA website for that. Instead I would tell this homeowner this shower assembly has failed and needs major repair. At the time of this post the remodel is only a couple of months old so my prediction is this will get worse. As the mud base gets more saturated more of the grout lines will begin to look like this one.

Source

National Tile Contractors Association - https://www.tile-assn.com/