Shower grout turns dark from three separate sources that stack on top of each other, soap scum from the alkaline residue of bar soap, mineral deposits from hard water evaporating on the surface, and mildew that grows in the porous grout where moisture stays trapped. Standard bathroom spray cleaners address none of these effectively because they do not penetrate the grout surface where all three problems live.
The Oxygen Bleach Method
Mix OxiClean powder or any oxygen bleach powder with just enough water to form a thick paste. Apply the paste to the grout lines using an old toothbrush, working in small sections and pressing the paste into the grout surface rather than just spreading it over the tile. Allow a minimum of 20 minutes of contact time, the oxygen ions released during this period oxidize the soap scum and mildew simultaneously while the alkaline environment loosens mineral deposits. For grout that has not been cleaned in months or years, a 45-minute contact time produces visibly better results.
Scrub with a grout brush after the dwell time and rinse with warm water. The grout should be noticeably lighter, often returning close to the original color that was there before the buildup began. A second application addresses any remaining staining.
For Mildew That Returns Quickly
If the grout re-darkens within 2 to 3 weeks of cleaning, the bathroom ventilation is insufficient to prevent mold growth. The exhaust fan is the first thing to address, covered in detail in the guide to cleaning your bathroom exhaust fan. Running it for 15 minutes after every shower rather than only during the shower reduces the moisture level enough to slow mildew growth significantly.
Sealing Grout After Cleaning
Applying grout sealer after a thorough cleaning is the step that makes the cleaning last. Sealer fills the porous surface of the grout and prevents soap, minerals, and mildew spores from penetrating, future cleaning then addresses only surface accumulation rather than embedded staining. Reapply every 12 months in shower areas. Both grout brushes and oxygen bleach powder are available on Amazon. For the full bathroom cleaning system that includes grout maintenance on a schedule, When You Were Never Taught to Clean ($11.99) covers it completely.
