How to Clean Caulk. Caulk in the bathroom can sometimes get a black or gray discoloration. This discoloration is mold, which you should clean as quickly as possible. If you don't clean the mold before it gets into the crevices beneath the caulk, you will have to remove the caulk and re-caulk the area.
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Wet the caulk thoroughly. All cleaners are water-based and work better on a wet surface.
Soak the caulk with household bleach cleaner. Allow the cleaner to sit on the caulk for 10 to 15 minutes.
Scrub the area with a damp sponge to remove any stubborn stains. Don't use a hard bristle brush or scouring pad as they may remove the caulk. Rinse the caulk thoroughly with warm water.
Proceed to a peroxide cleanup if the stain persists. Prepare a 50/50 solution of peroxide and water, and soak the stained caulk in the solution. Let it sit for 10 to 15 minutes, then scrub with a wet sponge and rinse thoroughly.
Remove the caulk if the stains persist. Any further cleaning efforts are likely to remove the caulk anyway.
Strip away the section of discolored caulk with a razor blade or a caulk removal tool, available at most hardware stores.
Scrape away all remnants of the old caulk with a razor scraper. New caulk can't bond with any leftover caulk.
Allow the area to thoroughly dry before applying the bead of new caulk. Follow the instructions on the caulk tube for cure time before getting the new caulk wet.