The 'Overnight Paste' Method for Bright, Clean Shower Grout

Why grout gets dingy

Grout is the cement-based filler between tiles, and unlike the tile itself it is porous. In a shower it soaks up a little of everything: soap residue, body oils, minerals from hard water and everyday grime. Nothing dramatic is happening. It just slowly loses its colour, the way a white t-shirt does. The paste below is a brightening refresh.

If you are dealing with the white, chalky film on the tiles themselves, that is soap scum and mineral buildup, which our guide to removing hard water stains covers. Do that first, rinse well, and then come back to the grout.

What you need

• Baking soda
• 3% hydrogen peroxide (the ordinary pharmacy strength)
• A small bowl and a spoon
• An old toothbrush or small grout brush to spread the paste
• A damp cloth or sponge, and gloves

Step by step

1. Test first. Hydrogen peroxide can lighten coloured grout. Try the paste on a small, out-of-the-way patch, such as a low corner, and check it after it dries.
2. Rinse and dry the area. Clear off loose soap scum so the paste reaches the grout.
3. Mix the paste. Stir about 2 parts baking soda to 1 part hydrogen peroxide into a thick, spreadable paste, like toothpaste. Mix it just before use.
4. Spread it on the lines. Use the toothbrush or your gloved finger to spread a layer along the grout lines. You are painting it on, not scrubbing.
5. Let it sit. Leave it for at least 15 to 30 minutes, or longer for very dull grout. Many people leave it for a few hours or overnight on floor grout where it will not slide. If it dries out on walls, mist it lightly with water.
6. Wipe and rinse. Wipe the paste away with a damp cloth, giving the lines a light brush where needed, and rinse with plain water.
7. Dry and admire. Dry the area with a towel. Repeat on any stubborn sections.

Common mistakes

• Scrubbing hard with a stiff wire brush. It wears grout away and can scratch tile. Let the paste do the work.
• Mixing the paste with vinegar for extra fizz. It is unsafe with hydrogen peroxide, and acid is hard on grout.
• Skipping the test on coloured grout. A lighter patch is hard to undo.
• Not rinsing. Baking soda residue leaves a white film.
• Leaving the shower wet. Grout that stays damp dulls faster. A quick squeegee and a little ventilation after showers keeps it bright longer.

What professionals use, and why

Professional cleaners usually use a pH-appropriate grout cleaner made for the job, a grout brush sized for the lines, and on bigger areas, steam or a tile-and-grout machine that cleans and extracts the dirty water at the same time. The extraction is the advantage: dirt is lifted out of the grout instead of being pushed around. Once grout is clean and dry, many apply a penetrating sealer, which makes it far less absorbent so it stays bright longer between cleans.

Workplace washrooms

• Use the overnight method at the end of the day, with a sign on the shower or washroom, so the paste can sit undisturbed.
• Keep ventilation running. Exhaust fans left on for a while after showers help grout dry, which is the biggest single help in staff showers and gyms.
• Squeegee shared showers at the end of each day.
• Ask about sealing. Grout in busy washrooms is often resealed on a regular schedule.
• Doing the whole washroom? The ring at the toilet waterline needs a different approach. See how to remove a stubborn toilet bowl ring.

If the grout darkens again quickly

Repeat the paste on stubborn sections. Very dull grout can take two rounds.

Seal it. Once grout is clean and fully dry, a penetrating grout sealer makes it much easier to keep bright.

Look at moisture. Grout that turns dark again within days, or stays damp, may point to a moisture problem: poor ventilation, a leaking shower door or fixture, or water getting behind the tiles. Fix the moisture and the grout stays clean.

Cracked, crumbling or missing grout needs regrouting, not cleaning. Gaps let water behind the tiles. If you see soft spots, loose tiles or a musty smell from the wall, have it looked at.

Frequently asked questions

How do you clean bathroom grout without scrubbing?

Mix about 2 parts baking soda with 1 part 3% hydrogen peroxide into a thick paste, spread it along the grout lines, and let it sit for at least 15 to 30 minutes, or longer for very dull grout. Then wipe it away with a damp cloth, rinse and dry. Test coloured grout first.

Is hydrogen peroxide safe on grout?

It is generally safe on white grout, but it can lighten coloured grout, so test a small hidden area first. Never mix it with vinegar, and do not use it straight after a bleach-based cleaner. Rinse in between.

Can I add vinegar to the grout paste?

No. Never mix hydrogen peroxide with vinegar, which forms an irritating acid. Acid is also hard on grout over time and etches natural stone.

How long should I leave the paste on grout?

At least 15 to 30 minutes. For very dull grout, many people leave it for a few hours or overnight on floor grout where it will not slide off. Mist it lightly with water if it dries out.

Why does my grout get dark again so quickly?

Grout is porous and absorbs soap and grime, and grout that stays damp dulls faster. If it darkens within days, check ventilation and look for leaks or water getting behind the tiles. Sealing clean, dry grout helps it stay bright.

Should I seal my grout after cleaning it?

Sealing is worth considering. Once grout is clean and completely dry, a penetrating grout sealer makes it less absorbent, so it stays brighter between cleans. Follow the sealer's directions.

If it is a workplace washroom you are looking after, you can find out more on our janitorial services page, and get more practical tips like this through our free cleaning tips sign-up.