My worst fear is that tiles will start coming off the ceiling. Am I right to again complain and ask for a repair at their expense?

I wouldn't worry about the cracking grout being a precursor to the tiles falling and needing a hardhat to take a shower!! LMAO

Although usually I would blame cracking grout on movement, it seems too widespread and too quick to be movement (unless he REALLY screwed up and all the framing around the shower is swelling, which I highly doubt). Most likely, it's something simple, like your installer mixed the grout too loose. That would most certainly cause the widespread cracking you're seeing, and would definitely be good cause to call him back AGAIN, and KEEP calling him back till he gets it right.

Bill V: Thanks for your quick response. In a situation like the shower grout cracking, do you think all the original grout needs to be removed for the repair?

In the floor situation, after the foreman determined it was a grout problem, they mixed another grout batch and put it on top of the original. So far, this treatment seems to be successful.

Is there a secret to getting the right consistency of grout? Like a recipe using certain proportions?

I'm sure the guy who sold us the tile will be glad when we move to carpeting where not as much can go wrong.

The most common reason for cracked or flaking unsanded grout that I see is using unsanded grout in joints that are are too wide for unsanded grout.

The second most common is the one Bill mentioned, mixing the grout too loosely. Too many guys do that, some get away with it, some don't. That can occur with either sanded or unsanded.

Those two will normally result in cracks showing within a few days of installation, as they are drying cracks, caused by the grout shrinking as it gives up water in the curing/drying process.

Cracks that show up later are usually structural, caused by the floor flexing, or as I've seen in a couple of situations, using mastic on floor tiles instead of thinset.

Grout bags give a recommended amount of water to add per bag. But it's usually a partial bag mix, so that may not work well.

I mix my grout a little thicker than most guys I've seen, but one thing I do is mix it a longer than most guys mix there grout, then I let it slake for the proper amount of time.

The irony is that by mixing it longer, which happens to be for the recommended amount of time on the bag, you get a better mix. And the grout, when mixed to the proper consistency and mixed for the proper amount of time, spreads like buddah. There's no need to add extra water to loosen it up.

Mongo

What's the best fix for the cracking grout in ceiling problem?

When I called the company who sold me the tile & hired the tilers, they just said "maybe we can fix it with some caulk?" From what I'm reading in other threads, that doesn't sound correct.

Help in how best to fix this is appreciated!!!

Score out most of the old grout, and regrout. If you use caulking, when you use he shower, you'll see the difference where the caulk is and where the grout is.