We bought our house going on 3yrs ago and had a terrible experience with an awful contractor. One of the things they worked on was our guest bathroom: replacing some drywall, subfloor, and ripping out the old shower/tub combo to put in a soaking tub and new shower fixtures and tile work.

When we first used the tub after they had finished, we noticed that the tub had cracks all along where it meets the grout that got noticeably bigger when it was filled with water. We asked the contractor about it and he said something about how it's cause the tub is heavier when filled and it's expected to happen, but they could put more grout to make it less apparent. Long story short, the tub was the least of our concerns by this point and was sort of forgotten in the craziness of other shenanigans they pulled.

We don't know enough about tile or grout or tubs to know if what he said holds any truth. Is this okay or should we do something about it? In the photos, the first will show the tub filled with water and the crack size and the second is the tub empty with the same crack. There are 3 different areas in the photos: front corner, middle of tub side wall, back corner.