Hi Cathy-- I'm assuming this is white grout with the small grout lines?

If so, once dry, any tub and tile caulk from a hardware store should be fine. If not, the best bet would be to find out where your GC got the grout, and get the caulk from the same place, the same manufacturer, and the same color and texture as the grout (by texture, I mean sanded or unsanded) so that it'll match.

As for what you saw when you washed it, if you hadn't added that part to your post, that wouldn't been my first step for you, just so that you WOULD get all that black crap out of there. You might even give it another shot just to make sure you've gotten it all, because that's one of the reasons why new caulking will turn so crappy so quickly sometimes. Once you've given it another shot and feel confident you got all the garbage out, let it dry for a few days, and then caulk it. That should be the end of your problems.

Thanks Bill, I just bought some caulk for tile and tub that looks pretty good. But I just noticed it says sanded. I have no idea if I should be using sanded or unsanded. What do you think? Some of the gaps are large between the bath tile floor and tub and the shower tile and tub. My tile and grout are white by the way.

The only reason for sand in the caulking is to match a sanded grout. It doesn't help anything, but it doesn't hurt anything, either. Short answer, yes, you can use it.

Thanks again Bill, But how do I tell if my grout is sanded or unsanded?

Cathy

If you've got real thin grout lines, then it doesn't have any sand in it. If the grout joints are 1/8" or more, then sanded grout was used, and the grout should have an abrasive texture to it.

Thanks Bill. I know that was probably a dumb question. I thought about it after and I guess you just look at it.

I forgot to mention that the corner shelf grout is also coming off. The entire corner going in about 2 inches crumbled out and there is a big space. I hope this is attached to the wall behind the tile somehow. I can't believe the tiler would have just grouted it to the tile surface. But this was in my old life, before I paid attention.

What do you think?

Cathy

Hey Cathy-- I answered that in the other thread you started. But for the benefit of those who might do a search later and find this thread, yes, you should be able to just remove all loose grout and caulk that joint, as well, SO LONG as that shelf is solid. If it's soft, caulking's not going to help a thing, and it needs to be pulled off and reset with thinset.