A continuous, watertight seal along the top edge of a bathtub or shower base is crucial. If the caulk is cracked or missing in spots, water will seep in and ruin the wall. Repairing a caulked joint is easy and takes less than 30 minutes. Start by scraping out all the old, dried-out caulk using an awl or narrow-bladed screwdriver. Then dip a cloth in rubbing alcohol and clean the surface of all soap scum and greasy grime. Allow the cleaned surface to dry a few minutes, and apply a thick bead of tub-and-tile caulk along the joint. Smooth the bead with a wet finger.