How to Treat Mold in Bathroom Grout

Why Grout Is the Most Mold-Prone Surface in the Bathroom

Grout is porous, sits in the wettest areas of the bathroom, and is nearly impossible to keep completely dry. These conditions make it the ideal environment for mold to establish and spread. Treating mold in grout requires a targeted approach — surface wiping alone won't reach the mold that has penetrated into the porous grout material.

Identifying Mold vs. Dirt in Grout

Mold in grout appears as black, dark green, or dark gray spots that don't wipe away with a damp cloth. It may have a fuzzy appearance and is often accompanied by a musty smell. Regular dirt discoloration is usually brown or gray and will lighten with scrubbing. If scrubbing with water alone doesn't remove it, it's mold.

What You'll Need

• Mold remover spray or bleach-based cleaner
• Grout brush
• Rubber gloves
• Safety goggles
• Microfiber cloths
• Grout sealer (for after treatment)

Treatment Method 1: RMR-86 (Fastest, Most Effective)

1. Ventilate the bathroom and wear rubber gloves.
2. Spray RMR-86 Instant Mold and Mildew Stain Remover directly onto all moldy grout lines.
3. Watch the mold stains disappear within minutes — no scrubbing required for most cases.
4. For deep-set mold, let sit 20–30 minutes before rinsing.
5. Rinse thoroughly and dry completely.

Treatment Method 2: Bleach Foam (For Widespread Grout Mold)

1. Ensure maximum ventilation.
2. Apply Scrubbing Bubbles Foaming Bleach Cleaner along all affected grout lines.
3. Let the foam cling and penetrate for 15–20 minutes.
4. Scrub with a grout brush.
5. Rinse thoroughly with clean water.

Treatment Method 3: Baking Soda + Vinegar (Mild Mold, Natural)

1. Apply a paste of baking soda and water to the moldy grout.
2. Spray white vinegar over the paste using a spray bottle.
3. Let fizz for 10 minutes, then scrub with a grout brush.
4. Rinse and dry. Best for early-stage mold only.

Critical Step: Seal After Treatment

After removing mold from grout, apply a professional-grade grout sealer once the grout is completely dry (wait 24 hours). Sealing closes the pores in the grout that allowed mold to penetrate, making future mold growth much harder to establish.

Preventing Grout Mold from Returning

• Seal grout annually.
• Run the exhaust fan during and after every shower.
• Squeegee shower walls after each use.
• Clean grout weekly with a diluted vinegar spray.
• Use a dehumidifier if bathroom stays persistently humid.

Recommended Products

• RMR-86 Instant Mold and Mildew Stain Remover (1 Gallon) — fastest grout mold treatment
• Scrubbing Bubbles Foaming Bleach Cleaner (2-Pack) — for widespread grout mold
• Grout Sealer (Clear, Professional Grade) — seal after treatment to prevent recurrence
• Foxtrot Living Grout Brush — hard bristles for scrubbing mold from grout
• Dehumidifier (95oz, 1000 sq ft) — reduce humidity to prevent mold regrowth