My home is 11 years old, and I've owned it for the last 9. The grout was already breaking up in a few places in the entryway when I bought it, so I know that it probably wasn't installed properly. I'm also pretty sure that the tile installer forgot to seal the entryway grout, because we're not having any problems with identical tile and grout in the "powder room", but the entryway grout has been grungy from day one. I've spent hours scrubbing it, to no avail.
I'd like to replace the broken grout and then use a colorant over all of it to hide the dirt, and avoid having to match the grout color. Is this practical? Or should I plan on redoing all of it? I saw another answer here that recommended using a grout saw to scrape off the top layer of grout to get it clean; is that better than coloring over the stains?
If it matters, the tile is 12" square, the cheapest stuff you can find, with about 1/4" grout lines. This was the builder's default material so you know there is no quality to be found here, but I'd rather not have to replace it all. The tiles themselves are in good condition.
Best Answer
If the grouting wasn't well done (or was OK initially, but then not sealed), I would be tempted to remove it with a grout saw and redo it properly.
Whether you should do just the part affected or the whole lot is a question of whether you want to repeat the exercise for the part you didn't do in the future. These types of jobs half done, or in this case half re-done, always tend to come back to haunt you. As an example, if the part nearest the doorway is worst affected, then likely it's a problem of moisture/water from shoes on entry. And you therefore might be able to get away with just redoing that portion.
As for using a colorant, this might work, but if the grout is in general moisture affected, i.e., now not properly bonded, it's could likely come out at some point in the future anyway...
Hope this helps!