Noticed this because the piece outside the shower was lifting and there was some water around the edge.
Is this as simple as getting a grout saw/knife and scraping out the old and putting in new grout?
Do I need to worry about any moisture underneath? Didn't own the home when it was installed so not sure what's going on underneath.
Best Answer
Grout is more an aesthetic here. It's porous, so it's not a prevention against water intrusion. Water will penetrate your grout. It's the stuff underneath the tile that should prevent water intrusion to the things that cannot get wet.
I would scrape or grout saw the old grout out. Ideally, you want to do this to the whole bathroom, as this new grout is unlikely to match the tone of the old.
The other answer mentioned caulk. The catch with caulk in an application like this is that caulk tends to be less durable than grout, especially if you use a simple latex caulk. I would grout rather than caulk in this case.