In short

Remove mold from shower grout by ventilating the bathroom, wearing gloves and eye protection, scrubbing with detergent and water, then using one mildew treatment and rinsing well. Never mix bleach with vinegar, ammonia or other cleaners. Mold that returns within days, spreads or comes with soft grout points to a moisture problem that needs professional attention.

Worth remembering

  • Open a window, run the fan and wear gloves and eye protection before using any cleaner on mold.
  • Scrub with detergent first, then use one treatment only. Never mix bleach with vinegar, ammonia or other cleaners.
  • Cut the moisture: run the fan, wipe the walls and repair leaks and failed caulk.
  • Mold that returns within days, spreads or comes with soft grout means water is getting behind the tile.

Surface mildew or a larger problem

Surface mildew shows as black, gray or dark green speckling on the face of the grout and along the caulk, and it wipes partly away with a cleaner. The color alone does not say what kind of mold it is.

A deeper problem looks different. Soft or crumbling grout, loose tiles, staining that returns within days, a musty smell that lingers after the shower has dried and a patch that keeps spreading all suggest water getting behind the tile. Cleaning the surface will not solve that.

Before you start

  • Open a window and run the exhaust fan. Fumes gather quickly in a small bathroom.
  • Wear rubber gloves, eye protection and a mask. People with asthma or a weak immune system should leave this job to someone else.
  • Test any treatment on a hidden spot. Bleach lightens colored grout and can harm natural stone.
  • Dampen the dark growth with soapy water before you brush it, since scrubbing it dry sends spores into the air.
  • Keep children and pets out of the room until the cleaning is done and the air has cleared.

Removing it step by step

Begin at the upper rows of tile, since runoff will streak whatever is below.

  • Scrub the grout with warm water, a little dish detergent and a nylon brush. This takes off most of the surface growth before any stronger product.
  • Rinse and wipe the area dry.
  • Apply one treatment to the dark grout that remains: three percent hydrogen peroxide as it comes, or household bleach diluted in water as its label directs. Never mix bleach with vinegar, ammonia or any other cleaner, because the fumes are dangerous.
  • Leave it for about ten minutes, scrub again and rinse thoroughly with clean water.
  • Dry the surfaces with a towel and keep the fan running.

Keeping it from coming back

Mold needs moisture, and removing the moisture does more than any cleaner.

  • Run the exhaust fan during every shower and for a good while afterward.
  • Squeegee or wipe the walls and the door after each shower.
  • Leave the door or curtain open so the shower dries between uses.
  • Fix dripping fixtures and replace caulk that has cracked or pulled away, since corners are where mold often starts.
  • Seal clean cement grout so water soaks in more slowly.

When to call a professional

Growth covering more than about ten square feet, mold that comes back quickly after careful cleaning and any musty smell with no visible source call for help with the cause. A plumber can trace a leak. A tile contractor or a mold remediation company can open a wall, dry it and rebuild what is damaged.

Cleaning the surface in the meantime only hides the sign, and the longer water sits behind tile, the more there is to rebuild. If anyone in the household has breathing problems that seem to follow the bathroom, mention it to a doctor.

Questions, answered

Is black mold on shower grout dangerous?

Color alone does not identify the kind of mold. Any mold can bother people with asthma, allergies or a weak immune system, so clean it promptly with good ventilation and protection. If the growth is widespread or symptoms continue, have the moisture source found and talk to a doctor.

Can I use vinegar instead of bleach on shower mold?

White vinegar can reduce surface mold on tile, but it etches cement grout and natural stone when used often. Keep products separate, and never combine vinegar with bleach, because the mix releases chlorine gas. Hydrogen peroxide is a gentler choice.

Why does mold keep returning to the same corner?

Corners stay wet longest, and caulk that has cracked lets water behind the tile. Check the caulk, the fan and any slow drip. If the mold returns within days of a careful cleaning, moisture is reaching it from behind and the cause needs fixing.

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