Originally Posted by peteco
Even silicone won't stick to itself. All residue must be cleaned off the surface for new silicone to stick properly.
Yep, and more pure silicone it is the worse it is to stick to. The "siliconized" caulk is normally latex with a bit of silicone in it.
I have mainly switched to urethane caulking which is much more adhesive and stronger than silicone, plus you can get another layer to stick. The slow cure ones can take a long time to dry, when I did our home shower it took over a week to fully cure, but was watertight in about 2-3 days.