Shower grout starts out light and clean, then slowly turns grey, yellow or black. The good news: in most showers the grout is not damaged — it is just dirty, and the right method brings it back. This guide covers the paste method that works for most showers, the stronger options for stubborn stains, and how to seal grout so it stays clean.
Quick Overview
- What it is: A step-by-step method to clean shower grout lines back to their original colour.
- Time needed: 30–60 minutes for a standard shower, plus 15 minutes of dwell time. Sealing adds 20 minutes and an overnight cure.
- What you need: Baking soda, white vinegar or hydrogen peroxide (3%), an old toothbrush or grout brush, a spray bottle, rubber gloves, and grout sealer for the final step.
Why Grout Goes Dark
Grout is porous, so it absorbs soap scum, body oils, hard-water minerals and mildew. In a shower, warm water and humidity speed all of that up. Dark patches in the corners and along the bottom rows are usually mildew and soap scum; orange or pink tints are often mineral deposits from hard water. Knowing which you have matters: soap scum and mildew respond to the paste method below, while heavy mineral build-up may need a longer dwell time or a second pass.
The Paste Method, Step by Step
- Clear and rinse the shower. Remove bottles and bath mats. Rinse the walls with warm water to loosen surface dirt.
- Make the paste. Mix baking soda with a little water until you have a thick paste, about the consistency of toothpaste. For a standard shower you will need roughly 1 cup of baking soda.
- Apply it to the grout lines. Spread the paste along the grout with your fingers (wear gloves) or an old toothbrush. Focus on the darkest lines first.
- Let it sit for 15 minutes. This dwell time does most of the work — it softens soap scum and lifts surface stains without heavy scrubbing.
- Scrub gently. Use an old toothbrush or a stiff grout brush, working along each grout line with short strokes. You do not need to press hard; let the paste do the work.
- Rinse thoroughly. Spray or pour warm water over the walls and wipe with a cloth until no paste remains. Check the lines while they are wet — clean grout looks noticeably lighter even before it dries.
For Stubborn Stains That Won’t Shift
If the paste method leaves grey or black lines, step up in this order:
- Hydrogen peroxide paste (3% pharmacy strength). Mix baking soda with hydrogen peroxide instead of water, apply, wait 15 minutes, scrub and rinse. This is stronger on mildew stains. Test it first on a hidden patch of coloured grout, because it can lighten some coloured grouts. Never mix hydrogen peroxide with vinegar.
- Oxygen bleach soak. For very stained floors or lower walls, dissolve oxygen bleach (the powder kind, not chlorine bleach) in warm water per the packet directions, pour it over the grout lines, and leave it for 30 minutes before scrubbing and rinsing. It is safe for coloured grout and tile.
- Steam cleaner. If you own a handheld steamer, steam loosens deep grime without chemicals and is a good option for old grout. Work in short passes and wipe up the loosened dirt as you go.
One honest note: if grout is cracked, crumbling or missing in places, no cleaner will fix it. Clean it as best you can, then re-grout the damaged sections before sealing.
Seal It So It Stays Clean
Sealing is the step most people skip, and it is why grout gets dirty again so fast. Once the grout is fully dry — wait at least 24 hours after cleaning — apply a penetrating grout sealer with a small brush or applicator bottle, following the product directions. One coat is enough for most showers; two coats are worth it on shower floors. Let it cure overnight before using the shower. Sealed grout resists water and soap scum, so your next clean will be much easier. Re-seal once a year in a shower that gets daily use.
What to Avoid
- Chlorine bleach. It whitens temporarily but can weaken grout over time, and the fumes in a small steamy bathroom are unpleasant. Oxygen bleach is the safer choice.
- Vinegar on natural stone. If your shower tiles are marble, travertine or another natural stone, skip vinegar — acid etches stone surfaces. Use the baking-soda-and-water paste instead.
- Metal brushes and abrasive pads. They scratch tile glaze and wear grout down, which makes it stain faster next time.
- Mixing cleaners. Never mix bleach with vinegar, ammonia or other cleaners — the fumes are dangerous. Use one method at a time and rinse between methods.
Keeping Grout Clean Afterward
Two small habits make the biggest difference. First, squeegee the shower walls after your last shower of the day — it takes 30 seconds and removes the water that carries soap scum into the grout. Second, leave the bathroom door or fan running for 20–30 minutes after showering so the grout dries fully instead of staying damp, which is what mildew needs to grow. With those two habits and a yearly seal, a deep clean like this one becomes a once-a-year job instead of a monthly battle.