Hello Houzz Community,

In June 2020 we moved back into our home that we renovated. Part of the renovation was a new master bathroom. We selected marble hex tile for the shower pan. Starting within weeks, the grout started to look dingy and in some places, a dark gray/black. I deep clean every week and have taken to scrubbing the grout by hand and even with an electric toothbrush. It sometimes lightens the color but often does very little, if anything. The darkest spots don't really change much. Unfortunately, due to the marble, I am not able to use baking soda/vinegar or any other popular solutions for stubborn stains. But I also feel that after such a short time of use, I shouldn't already have to take such drastic measures.

I used Simple Green Stone Cleaner and sometimes a diluted castile soap on the grout itself. Every week, and sometimes multiple times a week since it drives me nuts, I am scrubbing the grout. I even squeegee the floor after showering in case any standing water is causing this. With this new tile and install, I didn't expect to need to take such extreme precautions so soon.

Does anyone have any tips for me? Any idea what is causing this? I know the tilers used an Impregnator sealer on the tile after install. I'm hoping to get a bit more information from you experts before contacting the installer. It could be something I am doing but I am at a loss. The attached pictures show the tile and some of the particular trouble spots. The tile was slightly damp but hadn't been showered on in two hours. There is very little to no difference in color when wet vs dry. The darkest trouble spots are located on the same wall as the shower head.

Thank you in advance for your time and assistance!