How should I handle cracked grout in my two bathrooms?

Question

Both bathrooms have cracked grout where the tile meets the tub. They were done by a contractor 2.5 years ago. The second picture shows a crack going away from the tub between tiles.

This bathroom has hairline cracks.

This bathroom cracks thicker than a hairline.

Should I just put new grout over the cracks and press it in the cracks? Should I grind out the grout entirely and start fresh? Are there any special patch up products? I have never worked with grout before and I am clueless as to the best strategy.

Answer 1

Just caulk it. Grout will tend to crack in any change of plane, so caulk is the recommended practice. For prep, scratch out anything that's loose or protrudes past your caulk profile. You'll probably want to use white for the tub transition and a color matched caulk for the tile-to-tile corner.

A typical installation is caulked at the plane change and has room for both planes or at least the floor to expand comfortably. Grouting it with no expansion room is what you have. The "right" thing to do would be to scrape it out to give it more wiggle, but it's not absolutely necessary. It's a lot more work and possibly more likely to break your tile compared to just leaving it be, especially since it's been fine for a year so far.

Answer 2

There should be NO grout there it will always crack because you have 2 dissimilar materials that shrink and expand at different rates. The proper thing to use is caulking. Even where the wall meets the floor in the shower grout will work for awhile but will eventually fail as the floor moves different from the wall. But underneath the tile should be a rubber pan that will take care of these minor leaks as grout in and of itself is not water proof. The floor next to the tub is the area that would be the most concerning and needs to be caulked.