The very bottom line of caulking was looking bad around my bathtub, so I scraped out the old stuff and ran a new bead in there. The instructions called for 36 hours of time before you used the bathtub again, which was impossible, so I covered the new caulking with duct tape--being careful to kind of bow it so it would keep out the water without actually touching the caulking. Just to be safe, I left the tape in place for a week or so. I peeled it off, and the bathtub looked nice. For a couple of weeks. Then, the new caulking started to crack, warp, and turn black. It looks even nastier than it did before. It's screamingly awful. At this point, I must mention that God alone knows how old the bottle of caulking was. I had to clear out some dried gunk, but then it flowed nicely and was pure white. But, could this be the problem? Maybe old caulking doesn't hold up well? Or, am I missing some curing process that would make it work? It really sucks that I can't get this to work. The bathtub looks really nice at first. Then, it turns into an embarrassing nightmare. Any tips would be appreciated.