Grout turns grey for a boring reason: it is porous. Soap, hard water minerals and mildew settle into those pores, and a sponge only cleans the surface above them. That is why an hour of hand scrubbing produces a result that looks almost the same as when you started.
The fix is not more force. It is three things in order: chemistry, dwell time, and mechanical agitation that is not your wrist.
Step 1: pick the right cleaner for the type of dirt
- White or grey film: hard water and soap scum. Use an acid based bathroom cleaner or citric acid solution.
- Dark spots along silicone and corners: mildew. Use a bleach based cleaner or hydrogen peroxide.
- General dullness: alkaline all purpose cleaner is enough.
Never mix bleach and acid products. Pick one job per session. Check the care guidance for your tile first, and test any cleaner on a small hidden area: natural stone and specialty finishes can react differently from ceramic.
Step 2: let it dwell
Spray the grout lines and walk away for 5 to 10 minutes, or whatever the label states. This is the step everyone skips. The cleaner needs time to break down what is sitting in the pores. Scrubbing immediately after spraying means you are removing maybe a third of what you could. Keep the room ventilated.
Step 3: agitate with a powered brush, not your hand
This is where the actual difference comes from. Grout sits lower than tile, so flat sponges and cloths glide over it and never reach the recessed line. A narrow powered brush head follows the groove and spins at a speed your wrist cannot sustain for more than a few seconds.
A cordless spin scrubber like the GravN Spin Scrubber keeps a steady spin without pressure from you. Trace the grout line slowly, about 5 seconds per 30 centimetres, and work in small sections so you can see progress and rinse before residue dries. With the detail head from the GravN Brush Head Set you stay inside the groove instead of polishing the tile next to it.
Step 4: rinse hot, dry fully
Rinse with the hottest water your shower produces, then dry the lines with a cloth. Drying matters: leftover moisture in the pores is what restarts the mildew cycle.
Keeping it white: the 5 minute weekly pass
Once grout is actually clean, keeping it that way takes minutes. One weekly pass with the scrubber and plain bathroom cleaner prevents buildup from ever anchoring again. The deep clean above becomes a once a season job. See the tool in action on the Spin Scrubber page.
When grout cannot be saved
If grout is cracked, crumbling, or stained through its full depth, no cleaner fixes that. Regrouting or a grout pen is the honest answer. Cleaning works on dirt, not on damage.
FAQ
What is the easiest way to clean grout?
Use a surface appropriate cleaner, allow the stated dwell time, choose a narrow brush profile that fits the grout line, and work in small sections. Powered scrubbing removes the repetitive hand motion; surface testing and proper cleaner use still come first.
Does baking soda and vinegar work on grout?
The foam looks convincing but the reaction largely neutralises both ingredients. Use either an acid cleaner or an alkaline cleaner, not both at once.
Can I use a drill brush instead of a spin scrubber?
You can, but drills are heavy, corded near water, and spin faster than grout needs. A purpose built cordless scrubber is safer in a wet room and easier to hold at wall height.
How often should grout be deep cleaned?
With a weekly powered pass, a deep clean two or three times a year is enough for most bathrooms.
Is steam cleaning better than brushing?
Steam loosens dirt well but has no mechanical action, so you still need agitation afterwards. Brushing alone beats steam alone; steam plus brushing is best but rarely worth owning two devices.