If your shower caulk keeps turning black no matter how hard you scrub, the mold usually isn't just sitting on top anymore. It's in the caulk. And if the caulk keeps cracking, something is moving. Either way, the fix is the same: the old caulk comes all the way out, and new sealant goes onto a clean, dry seam.
Here's what that looked like on a recent job, and how to tell whether your shower needs fresh caulk or something more.
What does badly failed shower caulk look like?
My latest one was a house in North Park, about 100 years old, on the corner of a busy intersection. There's a new high-rise condo going up across the street and an apartment complex right next door. The homeowners have been there 10 years. We got talking about how people either love living on a busy street or hate it, and we both agreed we need some noise in the background to sleep.
They called me because one of the glass shower door panels was sagging from a loose bracket. The caulk at the base of the shower door was badly deteriorated, with a lot of mold on the inside.
For this one, I decided to take the glass door off to service it. The guide bracket at the bottom was already coming loose, and it was badly contaminated with mold and old caulking. With the door out, I cleaned up the track and removed the existing caulk between the track and the shower enclosure. Then I sanitized and wiped everything down thoroughly, reset the door guide, and put down new sealant. Last, I adjusted the door bracket, put some Loctite (a thread-locking compound) on the hardware so it would stay tight, and reinstalled the door.
The order is the point. New caulk went on only after the old caulk and the mold were gone and the surface was clean.
Why does my shower caulk keep turning black after I scrub it?
This is the one I hear the most. Typically, scrubbing isn't going to remove it. Even if it looks like it did, the mold is still embedded in small little pores in the caulk. It will keep regrowing until the caulk is completely removed and reapplied.
That's why bleach and a toothbrush only buy you a little time. You're cleaning the surface of a problem that lives inside the bead (the line of caulk).
Can you caulk over old caulk?
You can, but it won't fix anything. The most common mistake I see, from DIY jobs and cheap jobs alike, is new caulk applied over caulk that was already poorly applied or deteriorated, thinking it's going to make it better.
New caulk is only as good as what it's stuck to. If the old caulk underneath is moldy, loose, or pulling away, the new bead sits on top of all of it. The mold and the gaps are still there, just covered up. Cut the old caulk out, clean and dry the seam, then apply fresh sealant.
Why does shower caulk crack in Southern California homes?
Probably the biggest thing here in Southern California is shifting or movement. The joints where two surfaces meet (tile to tub, wall to wall in a corner, the door track to the enclosure) are where that movement shows up first.
That's also why those joints get a flexible sealant instead of grout. Tile industry installation standards call for a movement joint filled with sealant, not grout, at inside corners and anywhere the surface changes direction. I explained caulk vs. grout in more detail in Why a Good Handyman Quote Starts With Photos, Not the Fastest Number.
And it's why the product matters. On the North Park job I used GE Supreme Silicone Kitchen & Bath. GE rates it for 50% joint movement and lists "lifetime mold-free product protection." Read GE's fine print, though: the cured sealant resists stain-causing mold and mildew, but it still needs regular cleaning, because soap and other residue can grow mold on the surface. Even good caulk still needs a wipe-down.
What if the wall behind the caulk is soft or wet?
Before you scrape anything, press on the wall or floor right next to the failing caulk. Does it feel soft or crumbly? Does a stain get wet or grow after showers?
If the area around the failing caulk is soft or wet, it can sometimes be remedied by a handyman if it's a small area. If it has led to extensive mold growth, or more damage you can see without opening up the floor or wall, it may be better suited for a restoration company. I'd rather tell you that from your photos than show up with a caulk gun for a job caulk can't fix.
How often should you recaulk a shower?
There isn't one number that fits every bathroom. It depends on how the bathroom is used and kept up.
In a well-ventilated bathroom that's used and maintained consistently, caulk lasts a lot longer than it does in, say, a tenant-occupied property. If it's a home you live in and keep up on, you may not need it redone for several years. If the ventilation is poor, or it's a rental where the tenant doesn't take the same care, have it looked at more often. It may need to be redone once a year or once every couple of years.
Whatever the calendar says, it's time when you see:
- Black spots that come back after cleaning
- Cracks, especially in the corners and along the tub
- Caulk pulling away from the tile, the tub, or the door track
If your bathroom fan isn't clearing the steam, that's worth a look too. Here's when a bathroom fan just needs a little care.
While you're in the bathroom: is your toilet leaking without a sound?
Take two more minutes. A toilet can leak from the tank into the bowl without making noise or leaving water on the floor. The EPA's test is simple: put a few drops of food coloring in the tank, don't flush, and check the bowl. If color shows up in the bowl after about 10 minutes, you have a leak, often from a worn flapper (the rubber seal at the bottom of the tank). Flush when you're done so the dye doesn't stain.
While you're down there, check the base. If the toilet is loose at the floor, or you notice leaking, odor, or soft flooring around it, send over some photos.
Shower caulk questions people ask
Is it normal for shower caulk to crack?
Some movement happens in every house, and around here it's the biggest cause I see. Caulk that cracks early usually means the joint is moving more than that caulk can handle, or it went on over old caulk.
How do I get black mold out of shower caulk?
For good, you usually can't. Scrubbing may make it look clean, but it's still in the pores, and it comes back. Remove the caulk and replace it.
How long does shower caulk last?
In a well-ventilated bathroom that's kept up, often several years. With poor ventilation or in a rental, have it checked every year or two.
How long after caulking can I use my shower?
It depends on the product. For the GE Supreme I used in North Park, GE says it can be water-ready in as little as 30 minutes, but only with a small bead at 65°F or warmer and at least 50% humidity. Otherwise, keep water off it for 8 hours, and don't touch or clean it for 24 hours. Check the label on whatever you use.
Should I caulk or grout where the tile meets the tub?
Caulk. That's a joint where two surfaces meet and move, and grout there tends to crack. More in my caulk vs. grout explanation.
When is shower mold more than a caulk job?
When the wall or floor next to it is soft or wet over more than a small area, or the mold and damage have spread past the caulk to where you can see them without opening anything up. That usually belongs with a restoration company.
How much does it cost to recaulk a shower in San Diego?
Showers vary a lot: how many corners and seams there are, how much old caulk and mold has to come out, and access. So I price shower recaulking from photos. You can see what goes into it on the shower recaulking page and our pricing page.
Send over a couple of photos
If your caulk keeps turning black or pulling away, send over some photos: one wide shot of the whole shower and a close-up of each seam, plus your ZIP code. You can start here: Start Your Home Project.
We should get connected. And we'll take it from there.
