How do I keep shower grout from getting moldy?

Shower grout gets moldy because it stays wet. Mold needs moisture, and grout in a shower is wet every day, so the answer is mostly about drying it out fast and cleaning it before buildup gives mold something to hold on to. EPA says that when mold in a shower keeps coming back, increasing ventilation by running a fan or opening a window, and cleaning more often, will usually prevent it from recurring or at least keep it to a minimum.^[1]

Dry it out after every shower

Ventilate. EPA's advice is to run the bathroom fan or open the window when showering.^[1] Leave the fan running for a while after you finish, since the walls and grout are still wet. If the fan does not clear the mirror in a reasonable time, check that it actually vents outdoors and that the grille is not clogged with dust.

Get the water off. A squeegee on the walls and glass and a quick towel on the floor and curb take a minute and remove most of the water that would otherwise soak into the grout. Leave the door or curtain open afterwards so air can reach the tile.

Watch whole-house humidity. EPA suggests keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent,^[1] and the Virginia Department of Health suggests 30 to 60 percent and using exhaust fans to move shower moisture outdoors.^[2] Humid Virginia summers can make that hard without air conditioning or a dehumidifier, and a bathroom that never fully dries will grow mold whatever you clean it with.

Clean it before it builds up

LATICRETE notes that no cement-based grout is self-cleaning or absolutely stain-resistant,^[3] and it recommends a clear, pH-neutral cleaner for routine cleaning and a cleaner made specifically for mold or soap scum when those appear.^[3] A light, regular clean usually does more than a big scrub once a season.

Choose cleaners with care. Daltile says cleaners should be specified as safe for ceramic tile installations, including the grout,^[4] and warns against chemicals with fluorine compounds, which damage ceramic, glass and stone.^[4] Both makers say to test a cleaner on a small area first.^[3][4] Rinse thoroughly with clean water afterwards: Daltile notes that bleaches and alkaline cleaners can take several rinses to remove.^[4] Natural stone needs its own cleaners: LATICRETE says acid-based products are not recommended for polished marble and other types of stone.^[3]

About bleach

Bleach whitens mold stains, but it is not the main tool. EPA does not recommend chlorine bleach or other biocides as a routine part of mold cleanup,^[1] and it points out that dead mold can still cause allergic reactions, so it has to be removed, not just killed.^[1] Scrubbing is what removes it.

If you do use bleach or another disinfectant, ventilate the room and never mix chlorine bleach with cleaners that contain ammonia, because toxic fumes can result.^[1] For bleach or strong cleaners, EPA recommends gloves made of natural rubber, neoprene, nitrile, polyurethane or PVC,^[1] and goggles.

Keep cement grout sealed

Sealing does not make grout waterproof, but it slows down how much water and grime soak in, which makes it easier to clean. As an example of what sealers do, a water-based grout sealer for cement grouts resists water- and oil-based contaminants without changing the grout's look, and still lets moisture vapour pass.^[6] Follow the label for drying time before the shower is used.

You do not need a calendar to know when to reseal. Daltile's test is simple: drop a little water on the grout; if it beads up, the sealer is fine, and if it soaks in, it is time to reseal.^[5] Clean the grout and let it dry fully before sealing, or you seal the dirt in.

Do not caulk over mold

The flexible caulk in the corners, along the floor and around the curb is often where mold shows first, and mold that has grown into caulk does not scrub out. EPA says not to paint or caulk moldy surfaces;^[1] clean the joint, dry it, and recaulk. LATICRETE's guidance for bathrooms is an anti-microbial caulk for bathrooms and flexible silicone caulk at corners and changes of plane.^[7] For the method, see how to recaulk a tub or shower, and for timing, how often to recaulk a shower.

When it is more than surface mold

For a moldy area smaller than about 10 square feet, EPA says that in most cases you can handle the job yourself,^[1] and VDH says small areas on hard surfaces can be cleaned with detergent and water or a mild bleach solution.^[2] If mold covers more than about 10 square feet, or there has been a lot of water damage, EPA points to its separate guide, Mold Remediation in Schools and Commercial Buildings, which it says applies to other buildings too.^[1]

Mold that comes back within days in the same spot, grout that stays dark long after a shower, or a musty smell from the wall can mean water is getting behind the tile. In that case, cleaning will not fix it; see why a tile shower leaks and why a bathroom keeps getting moldy after disinfecting.

Stop and call a pro if

• Mold covers more than about 10 square feet, or is growing on drywall, a ceiling or inside a wall.
• Tiles are loose, grout is crumbling, or the wall or floor feels soft. The waterproofing behind the tile may have failed.
• There is a leak into the room below.
• Anyone in the house has asthma, a weakened immune system or other health concerns about cleaning it.

You can browse shower tile installers, look up flooring and tile businesses around Blacksburg, or read the other flooring and tile answers. If the grout needs cleaning, regrouting or more, describe the job on Loclis.