I have been caulking my shower floor base where it meets the shower wall. Both are fiberglass. I have removed all old caluk cleaned and dried the surface and have even used rubing alcohol. I caulk..wait 48 hrs. after 3 showers tha caulk is coming off. I am using a top rated caulk that says that it is for tub and showers...but it is not curing. This is the 3rd time in a month that I have caulked..What am I doing wrong?