Mold on Silicone, Grout and Bathroom Ceilings: How to Remove It

Mold on silicone caulk in a shower can be cleaned if it sits on the surface, but if the black spots are under or inside the bead, the caulk has to be cut out, the joint cleaned and dried, and new caulk applied. Grout and painted ceilings usually clean up with detergent or a diluted bleach solution, as long as you also fix the moisture that feeds the mold: poor ventilation, leaks or failed seals.

Why bathrooms grow mold so easily

Mold needs moisture, and a bathroom delivers it several times a day. The EPA says mold can be prevented by controlling moisture, keeping indoor humidity below 60 percent (ideally 30 to 50 percent), and running a fan or opening a window when you shower (EPA, A Brief Guide to Mold, Moisture and Your Home). Soap scum and body oils on caulk and grout give mold something to grow on, and corners that never fully dry become permanent black lines.

Common sources of bathroom mold:

• No exhaust fan, or a fan that does not vent outdoors. Steam has nowhere to go and condenses on the ceiling and walls.
• Short fan run times. Turning the fan off as soon as you leave the shower leaves the room wet.
• Failed caulk or cracked grout. Water gets behind the seal and stays there.
• Hidden leaks. A dripping valve, drain or supply line inside the wall can grow mold you cannot see.
• Cold surfaces. Exterior walls and ceilings under an attic can collect condensation.

Mold on silicone caulk: surface or deep?

Mold on caulk usually feeds on the film of soap and body residue that builds up on it, and it can also grow underneath a bead that has lost adhesion. Before you scrub for an hour, find out which you have.

Caulk manufacturer Sashco suggests a simple test: soak a cotton ball in chlorine bleach and hold it on the mildewed caulk. If the stain disappears right away, the growth is on top of the caulk. If it takes 45 seconds or more, it is likely under the caulk (Sashco). Ventilate, wear gloves, and do not combine this with any other cleaner.

If it is on the surface

1. Open a window or run the exhaust fan.
2. Scrub with a detergent solution or a bathroom mold and mildew cleaner, following the label.
3. If you use bleach, the CDC says use no more than 1 cup of bleach in 1 gallon of water and never mix it with ammonia or other cleansers (CDC).
4. Rinse and dry the bead completely.

If it is under the caulk

Cleaning will not reach it. The fix is to replace the bead:

1. Cut out the old caulk with a utility knife or caulk removal tool and remove all residue, since new silicone does not bond well to old silicone.
2. Inspect the joint. Sashco notes that water often gets behind caulk that has cracked or lost adhesion, and the source may be behind the tile or in unsealed grout lines (Sashco).
3. Clean the joint, rinse it and let it dry fully. Do not caulk over mold or damp surfaces; the EPA says to clean and dry surfaces before you paint or caulk (EPA).
4. Apply a new bead of bath and kitchen silicone labeled mildew resistant, and let it cure for the time on the tube before showering.

If you find soft drywall, loose tile or widespread black growth on the back of the tile when you pull the caulk, Sashco advises calling in a specialist (Sashco). That usually means water has been getting into the wall for some time.

A side note: some searches for "silicone mold" are about silicone casting molds for resin or baking. Those are cleaned with mild soap and water according to the maker's instructions; this guide is about mold growth on bathroom caulk.

Black mold in the shower and on the tub

Black spots in the shower are very common, and color alone does not identify the species or how risky it is. See our black mold guide for what is known about that. The cleaning approach is the same whatever the color.

Grout is porous. After cleaning, Sashco recommends sealing grout to help stop moisture from getting in (Sashco).

Bleach or vinegar?

Both are used in bathrooms. The EPA's general advice for hard surfaces is detergent and water, and it does not recommend bleach as a routine mold-killing step in remediation (EPA). What matters most is never mixing products. Poison control warns that bleach and vinegar together create chlorine gas, which irritates the airways, eyes, nose and throat (Poison Control). Our guide on whether vinegar kills mold goes into that comparison in detail.

Bathroom ceiling mold

Black specks on a bathroom ceiling usually mean steam is condensing there and not drying out. To remove bathroom ceiling mold:

1. Protect your eyes and lungs. The EPA recommends gloves, goggles and an N-95 respirator for mold cleanup (EPA). Working overhead means drips fall toward your face.
2. Wipe the area with a detergent solution or a bathroom mold cleaner. Avoid soaking the drywall.
3. Let it dry fully, ideally with the fan running and a window open.
4. Repaint only after the surface is clean and dry. Paint over mold tends to peel (EPA).

If the ceiling is stained, sagging or soft, water may be coming from above, such as a leaking toilet or tub on the next floor or a roof leak. That is a different problem; see our water stains on ceiling guide and the ceiling water damage overview.

Fix the ventilation or the mold comes back

Cleaning without fixing moisture means you will be doing it again in a few weeks. The steps that make the biggest difference:

• Run the exhaust fan during every shower and for a while after. The EPA recommends a fan or open window while bathing (EPA), and the Insurance Information Institute also recommends bathroom exhaust fans for mold prevention (Triple-I).
• Make sure the fan vents outdoors. A Department of Energy guide notes that moist air from a duct ending in the attic can condense on cold rafters and sheathing and encourage mold there. The duct should end at a dampered roof cap or a soffit or wall vent (DOE Building America Solution Center). See attic and crawl space mold.
• Squeegee or towel off walls and glass after showering.
• Keep humidity in range. A low-cost hygrometer shows whether the room stays above 60 percent after showers.
• Fix leaks quickly. A drip under the sink or behind the toilet can rot the subfloor.

When bathroom mold is more than a cleaning job

Small bathroom mold is a cleaning chore. Larger or hidden growth is a mold remediation job.

Call a professional if:

• The moldy area is larger than about 10 square feet. The EPA says most people can handle smaller areas themselves (EPA).
• Mold keeps returning in the same spot even after recaulking, a sign of a hidden leak.
• Tiles are loose, the floor near the tub is soft, or there is a musty smell from the wall.
• Sewage has backed up into the tub or shower. Sewage backup in a tub is contaminated water, not a mold-cleaning job; the EPA advises a professional with experience in contaminated-water cleanup (EPA). Read our sewage backup guide and sewage cleanup page.
• Anyone in the home has asthma, mold allergy or a weakened immune system. The CDC notes people with asthma or mold allergies may have severe reactions (CDC). If you have symptoms, see a doctor.

Professional mold remediation for a bathroom typically involves removing wet drywall behind the shower, drying the wall cavity and finding the leak. If the cause was a leak that has soaked the floor or walls, water damage restoration may come first.

Getting help

Flood Rescue Pros is a free service that connects homeowners with independent local water damage and mold restoration companies. We do not do the work ourselves. If you want a local company to look at a recurring bathroom mold problem, get help now or find your area on our locations page.

Frequently asked questions

How do you remove black mold from shower silicone?

Test it first. If a bleach-soaked cotton ball clears it quickly, scrub and dry the surface. If the stain stays 45 seconds or more, the mold is likely under the caulk, so cut the bead out, clean and dry the joint, and recaulk.

Which kills mold better, bleach or vinegar?

The EPA's guidance for hard surfaces is to scrub with detergent and water and dry completely, and it does not recommend bleach as a routine step. If you use bleach, the CDC says no more than 1 cup per gallon of water. Never mix bleach with vinegar or ammonia.

Why does mold keep coming back in my shower?

Usually because the moisture source was not fixed: a fan that is too weak or vents into the attic, short fan run times, or water getting behind failed caulk or grout. Mold under a caulk bead will return through new caulk if the joint was not cleaned and dried first.

How do professionals remove mould in bathrooms?

For small areas they clean and recaulk. For larger or hidden growth they set up containment, remove moldy drywall behind tile, HEPA vacuum, dry the cavity and fix the leak, following standards such as IICRC S520.

Can I paint over bathroom ceiling mold?

No. The EPA says not to paint or caulk moldy surfaces; clean and dry them first, because paint over mold is likely to peel.

Key facts

• Mold on top of silicone caulk can be cleaned; mold under the bead means cutting out and replacing the caulk.
• Sashco's test: a bleach-soaked cotton ball that takes 45 seconds or more to clear the stain points to mold under the caulk.
• The CDC says use no more than 1 cup of bleach per gallon of water, and never mix bleach with ammonia, vinegar or other cleaners.
• The EPA recommends running a fan or opening a window while showering and keeping humidity below 60 percent.
• Bathroom fans must vent outdoors; venting into the attic can cause attic mold.
• Mold areas over about 10 square feet, recurring growth, soft walls or sewage backup call for a professional.