How to Remove Black Mold from Shower Grout

Mold thrives in the constant humidity of a bathroom, feeding on soap scum and skin cells trapped in porous grout lines. While store-bought sprays promise instant results, they often just bleach the surface of the mold while the roots remain embedded deep in the grout, ready to bloom again the moment the shower gets warm. To do this well, you need to penetrate the grout matrix and kill the spores at the source. This is less about aggressive chemical warfare and more about consistent, targeted cleaning that strips away the protective biofilm. Once the mold is cleared, keeping your shower dry is the only way to prevent it from returning.

1. Wipe Away Surface Buildup. Wipe down the shower walls with a basic dish soap and water solution to remove surface-level soap scum. This allows your cleaning agent to make direct contact with the mold in the grout.
2. Make Your Mold-Fighting Paste. Combine one part hydrogen peroxide with two parts baking soda in a small bowl until it forms a thick, spreadable paste. Do not use vinegar in this mixture as it neutralizes the fizzing action needed to lift debris.
3. Coat Every Moldy Line. Using a gloved finger or an old paintbrush, apply the paste directly onto the affected grout lines. Make sure the mold is completely covered by a thick, opaque layer of the paste.
4. Let Chemistry Do the Work. Allow the paste to sit on the grout for at least 30 minutes. During this time, the oxygenating action of the peroxide will work to break down the mold structures.
5. Dig Into the Grout. Use a stiff-bristled nylon grout brush to scrub the paste into the grout lines in a circular motion. Apply moderate pressure to dislodge the loosened mold spores from the porous material.
6. Flush and Check Your Work. Rinse the area thoroughly with cold water, ensuring all paste residue is removed. Inspect the lines once dry; if dark spots remain, the mold may be deep enough to require a second application.