How to Remove Mold from Grout (Fast and Permanently)

Black mold in bathroom grout is one of the most stubborn cleaning challenges. The mold penetrates the porous grout surface and resists regular cleaning products. Here's how to remove it completely.

What You'll Need

• RMR-86 Instant Mold and Mildew Stain Remover — 1 gallon, scrub-free formula that eliminates mold stains on contact
• Foxtrot Living Grout Brush with Long Handle
• Hydrogen peroxide (3%)
• Baking soda and white vinegar
• JohnBee Spray Bottles
• Rubber gloves and eye protection

Understanding Grout Mold

Grout mold is not just surface discoloration — mold spores penetrate the porous grout and grow within it. This is why surface wiping doesn't work. You need a product that penetrates the grout and kills the mold at the root, or one powerful enough to bleach out the stain completely.

Method 1: RMR-86 (Fastest — No Scrubbing)

1. Ventilate the bathroom thoroughly — open windows and run the exhaust fan. RMR-86 has strong fumes.
2. Wear rubber gloves and eye protection.
3. Spray RMR-86 directly onto the black mold stains in the grout.
4. Watch the stains disappear within 15–30 seconds — no scrubbing required.
5. For stubborn stains, let sit up to 1 minute.
6. Rinse thoroughly with water.

RMR-86 is the most powerful mold stain remover available for consumer use. It works on contact and eliminates stains that baking soda, vinegar, and bleach cannot touch.

Method 2: Hydrogen Peroxide (Safer, Effective)

1. Spray 3% hydrogen peroxide directly onto the moldy grout.
2. Let sit for 10–15 minutes.
3. Scrub with the grout brush.
4. Rinse thoroughly.
5. Repeat for stubborn stains.

Hydrogen peroxide kills mold and lightens stains without the harsh fumes of bleach or RMR-86. It's the best middle-ground option.

Method 3: Baking Soda + Vinegar (For Light Mold)

1. Apply baking soda paste to the moldy grout.
2. Spray with white vinegar and let fizz for 5 minutes.
3. Scrub firmly with the grout brush.
4. Rinse and repeat.

Effective for early-stage mold and surface discoloration. Not strong enough for established black mold.

After Removing Mold: Seal the Grout

Once the grout is clean, apply a grout sealer to close the pores and prevent mold from penetrating again. This is the most important step for long-term prevention. Reapply annually.

Frequently Asked Questions

Is black mold in bathroom grout dangerous?

The black mold commonly found in bathroom grout is usually Cladosporium or Aspergillus — not the toxic Stachybotrys (black mold) associated with serious health risks. However, any mold should be removed promptly as it can cause respiratory irritation, especially for sensitive individuals.

Why does mold keep coming back in my grout?

Mold returns because the conditions that cause it — moisture and humidity — haven't changed. After removing mold, seal the grout, run the exhaust fan during and after every shower, and squeegee tile walls after use. These three steps prevent recurrence.

When should I re-grout instead of cleaning?

If mold has penetrated so deeply that cleaning doesn't restore the grout color, or if the grout is crumbling or cracked, re-grouting is the better solution. Cracked grout also allows water to penetrate behind tiles, causing structural damage.