Silicone caulk is a sealant often used in bathrooms and kitchens. It may also be used to seal mirrors and windows in place. Moisture can lead to mildew growth on some silicone caulks. These black stains ruin the appearance of the caulked area and can spread if left untreated. To prevent it from spreading and damaging the silicone, remove new mildew growth as soon as you notice it.
Wipe down the silicone caulk with a cloth dipped in hot water. Remove any surface dirt from the area.
Combine ¼ cup chlorine bleach with 1 gallon cold water.
Soak a rag in the bleach solution then lay it over the mildewed area. Soak the silicone with the rag for three to five minutes.
Scrub the silicone lightly with the rag, removing any remaining mildew stains. Rinse the area with hot water.
Soak the silicone a second time if mildew stains are still visible. Scrub and rinse. It may take two to three soakings to remove all the mildew stains.
Wipe the moisture from the silicone after it gets wet to prevent mildew from forming in the first place. If you replace the caulk for any reason, use a variety labelled as mildew-resistant.
Do not leave the bleach mixture on the silicone as it can break it down and cause it to peel off.