How to Get Mold Stains Off Shower Caulk (and When to Replace It)

Step by step

1. 1

   Get air moving and gear up

   Open the window or turn on the bathroom fan, and leave it running the whole time. Put on rubber gloves and goggles. For mold cleanup, the EPA suggests goggles without vent holes and an N-95 respirator, so you do not breathe in or splash what you scrub loose.

2. 2

   Scrub the caulk with soap and water

   Mix a little dish soap into a small bowl of warm water. Dip a tile and grout brush in it and scrub along the caulk line with short strokes. The EPA says to scrub mold off hard surfaces with detergent and water. GE Sealants, a caulk maker, says soap scum gives mold food, so you want it gone.

3. 3

   Rinse and dry it

   Rinse the caulk with clean water until no suds are left, then wipe it dry. Rinsing matters, because you never want soap or any other cleaner still sitting there when bleach goes on in the next step.

   What it looks like: if the caulk is clean now, you are done. Skip to the habits under “It keeps coming back” below.

4. 4

   Treat the stains that stayed with a weak bleach mix

   Clorox says to mix 1/3 cup of its bleach into 1 gallon of water. Stir it in a bucket, then dab or brush it onto the dark spots. Keep the caulk wet with it for 10 minutes, adding a little more if it dries out. Test a small hidden spot first.

   Do not make it stronger, because Clorox says a stronger mix is not recommended. Never use it on marble, and never let it meet another cleaner.

1. 5

   Rinse well and dry

   Rinse the caulk and the tile around it with warm water, then wipe everything dry. Do not save the leftover mix, because Clorox says to use a freshly mixed one each time.

   What it looks like: look closely. If dark spots still show in the caulk, the maker of Clorox Plus Tilex says mildew that gets behind caulk is hard for a cleaner to reach. Go on to Step 6.

2. 6

   Cut out the old caulk

   Lift off any loose caulk with a flexible putty knife. Then score along the edge of the caulk with a utility knife held flat to the tile, and scrape the strip out with the putty knife.

   DAP, a caulk maker, says a caulk remover can soften stubborn caulk if you let it sit for 5 to 20 minutes first.

3. 7

   Clean the bare joint and let it dry

   Wipe the joint with a rag and rubbing alcohol to take off the last film of old caulk, as DAP says. If you see mildew in the bare joint, wash it with the bleach mix from Step 4, rinse, and wipe it dry.

   Then let it dry all the way. DAP says the area must be clean and dry before new caulk goes on.

4. 8

   Lay in new 100% silicone caulk and wait

   Run one smooth, steady bead of 100% silicone caulk along the joint, then smooth it with a damp finger. GE Sealants says to use silicone rather than latex caulk in a shower. Wait as long as the tube says before water touches it. One DAP silicone says 12 hours, and a faster one says 30 minutes.

When it will not work, and what to do instead

Sometimes the black line wins the first round. Here is what to do then.

• The black is under the surface. The maker of Clorox Plus Tilex says mildew can grow behind caulk once its seal breaks, and a cleaner has a hard time getting to it there. Replace the caulk (Steps 6 to 8).
• You thought bleach would end it for good. That makes sense, since bleach turns the spots white fast. But the EPA says bleach is not recommended as a routine practice, and dead mold can still cause allergic reactions in some people. Scrub first, every time.
• You want to caulk right over it. It is tempting, but the EPA says not to paint or caulk moldy surfaces. Cut the old caulk out first.
• It keeps coming back. GE Sealants says to run the fan during and after showers and wipe the caulk dry. The EPA says to keep indoor humidity under 60 percent, ideally 30 to 50 percent. Why shower mold keeps coming back goes deeper.
• It is bigger than a caulk line. The EPA says to call a professional if the moldy area is bigger than about 10 square feet or there has been a lot of water damage.

Why it works

A shower gives mold what it likes. GE Sealants says caulk is porous enough to trap moisture, and soap scum gives mold food. That is why the caulk line is such an easy place for spots to start.

Scrubbing and a weak bleach mix deal with what sits on the surface. But caulk works a little like a sponge. Once mildew has worked its way in, or water has slipped behind a broken seal, you cannot clean it from the outside. You replace it.