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Cleaning mildew off bathroom silicone caulk

Nestor_Kelebay's picture
Nestor_Kelebay

This web site would do well with a Cleaning forum.  That's something we all do a lot of, and it's also something where valuable knowledge can be shared.
For example, it's a common misconception that mildew can't be cleaned off the silicone caulk around your bathtub/shower, and that the only way to remove that mildew is by replacing the silicone caulk.
I know that's not true because I clean the mildew off the silicone caulk in my bathrooms several times a year; pretty well every time a tenant moves out.  Keeping my bathrooms clean and attractive helps me rent my apartments, and nothing looks worse than mildew on the grout or on the silicone caulk around a tub or shower.
To do it, you just mix bleach (straight out of the jug) with Borax (which you can find in the laundry detergent aisle of any grocery store) to make a paste.  The active ingredient here is the bleach.  You can use talcum powder (aka: baby powder) or baking soda instead of borax, but talcum powder is heavier than bleach so it tends to settle to the bottom, resulting in the slurry at the top being too watery and the slurry at the bottom being too thick.  Baking soda is lighter and doesn't settle to the bottom like talcum powder does.  I find that 20 Mule Team Borax actually works about the best because there won't be any settling at all, AND when you mix bleach with Borax, the resulting paste is actually quite sticky, and sticks to vertical surfaces well.  It will even stick to the underside of a soap dish, if you have mildew growing on any silicone caulk there.
After mixing up the paste, use a large spoon to scoop the paste out of the mixing container and a tea spoon to move the paste out of the big spoon and onto the caulk.  Use that teaspoon to spread the paste onto the caulk, too.  Do that all the way around your bathtub, or wherever there is mildew growing on the caulk.
Now, cover up that paste with any cling-wrap (like Saran Wrap, but other brands work equally well, including NoName) to prevent the bleach from drying out.  Press any air bubbles out from under the cling wrap, trying to be sure that thee's an air tight seal on both sides of the paste.
Leave the bleach/Borax paste on the caulk at least overnight, and for several days if possible.  Then, pull off the cling-wrap and remove the paste.  Your old silicone caulk will be white as Manitoba snow.
I've found that it's not a good idea to try to save and reuse the paste.  Bleach gradually decomposes into salt water, and mixing it with talcum powder, baking soda or Borax seems to accelerate that process so that the used paste loses it's effectiveness after the second time you use it.  It seems to be most effective when freshly mixed.  Neither bleach nor Borax is expensive, and a cleaning will last at least a year before you start to see mildew forming again.  But, you can clean the same silicone caulk repeatedly.
I've been renovating and managing a small apartment block for over 20 years, and so I know how to replace silicone caulk, and have done it many times.  But I find that cleaning the mildew off of silicone caulk is an easier and equally effective way of restoring the appearance of the caulk.
Try my idea, and then if anyone tells you that you can't clean mildew off of silicone caulk, set them straight.

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