ᐅ Joints still appear darker in some areas even after drying.

I tiled a basement room and then grouted it. Even after several days, the color of the gray grout is much darker in some spots than in others. At first, I assumed there was still moisture inside and that the color would even out once it fully dried. But somehow, nothing seems to be changing—what could have gone wrong?

Is it an older building? Could moisture be coming up from underneath in some areas?

Was the grout properly mixed according to the processing instructions?

Could it be that the tile adhesive was pushed up in these areas?

This often results from different amounts of water in the mixtures. Sometimes it settles after a few months.

Thank you for your comments. I’ll try to respond here.

- Yes, it is an old building, and the moisture is mostly near the edges, close to the wall. However, the dark spots are also found in the center areas.
- The grout was mixed as closely as possible according to the instructions on the packaging. However, I had to add water because the mixture was far too stiff. But if that were the cause, the discoloration should be uniform everywhere. I only mixed it twice for the entire room, so it can’t be due to different batches.
- The tile adhesive was pushed up between the tiles in some places. I originally wanted to scrape it out, but after realizing how rock-hard it was and that the edges of the tiles could be slightly damaged, I left it as it was. My thought was to apply the grout over it and it wouldn’t be visible anyway.