Once you’ve removed all the caulk, clean up the mess you’ve made so it doesn’t interfere with the new caulk bonding to the surfaces. Dust the surface with dry paper towels or microfiber clothes so you don’t have to use too much liquid. Then use a light amount of cleaner and/or soap scum remover to clean the surface areas. Wipe the area dry when finished.Because the gap between the surfaces is now exposed, you want to expose it to as little moisture as possible. Spray paper towels of cloths with cleaner instead of spraying the surfaces directly.
Avoid using ammonia-based cleaners, since this creates toxic fumes when combined with bleach, which you’ll be using next.
 Kill mold by combining ⅓ cup (79 ml) of bleach with 1 gallon (3.75 L) of water. Fill a spray bottle with the solution and spray into and around the gap, or soak a paintbrush or foam brush in it and use that to reach inside the gap. Scrub with a cleaning brush, wipe up any extra debris that may have worked loose, rinse the area with dampened towels, and then wipe it dry.Alternately, you can also use a storebought mold-and-mildew killer., To make sure you’re not trapping any moisture behind the surfaces, wait until the next day before covering the gap with new caulk. Give the area behind the surfaces a chance to air-dry. Aim a fan at the gap to improve air circulation. To hurry things up, pass your heat gun up and down along the gap periodically and/or set up a space heater nearby.If you’re using silicone caulk for a new caulk line, the area must be completely dry in order for it adhere.
Water-based caulks will adhere to surfaces that are slightly damp, but doing so may increase the risk of mildew growing back.
Clean up after removal.
Get rid of mildew.
Allow the area to dry before recaulking.
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