How do I clean grout?
How to get discoloured tile grout clean again, what to use on mould versus general grime, and when grout needs replacing instead.
- Difficulty
- beginner
- Time
- 1 hr
- Read
- 3 min
- Safety
- caution
Short answer
Scrub with a stiff narrow brush and a paste of bicarbonate of soda and water for general grime, or a dilute bleach solution for mould staining. Leave whichever you use to sit for 10 minutes before scrubbing, then rinse. Grout that's crumbling or missing needs raking out and replacing, not cleaning.
Grout is porous cement. It stains because it absorbs whatever is regularly on it: soap scum and body oils in a shower, grease in a kitchen, dirt underfoot on a floor. The colour change is usually in the top fraction of a millimetre, which is why a mechanical scrub with a mild abrasive works better than most sprays — you're removing a layer, not dissolving a stain.
Safety
What you'll need
- Stiff narrow brush (a grout brush or an old toothbrush)
- Bicarbonate of soda
- Household bleach or oxygen bleach (optional)
- Grout pen for finishing (optional)
- Cloths and a bucket of clean water
Step by step
- Clean the tiles normally first and let them dry.You want to see the actual state of the grout, not surface dirt sitting on it.
- Mix bicarbonate of soda with a little water into a thick paste.Thick enough to stay on a vertical grout line without running.
- Work the paste into the grout lines with the brush and leave it 10 minutes.Bicarb is a mild abrasive — the sitting time softens grime so you scrub less hard.
- Scrub along the grout line, not across it.Along the line keeps the brush in contact with the grout instead of skating over the tile.
- For remaining dark or black spots, apply a 1:4 bleach-to-water solution and leave 10 minutes.Black spotting in a bathroom is mould, and abrasion alone won't kill it.
- Rinse thoroughly with clean water and dry the surface.Residual bicarb dries to a white haze; residual bleach keeps working on anything it touches.
- Once fully dry, consider sealing the grout with a grout sealer.Sealing is what stops you doing this again in six months. It's the step most people skip.
Tips
- An electric toothbrush head or a rotary tool with a nylon brush turns a two-hour job into a twenty-minute one on a large area.
- Oxygen bleach (sodium percarbonate) is gentler on coloured grout than chlorine bleach and won't fade it.
- A grout pen is a cosmetic fix, not a clean — but on grout that's permanently stained rather than dirty, it's an honest and effective option.
- Steam cleaners work well on floor grout and use no chemicals, though they will not remove staining that has soaked in.
Common mistakes
- Using a wire brush — It gouges the grout and scratches glazed tiles permanently.
- Using acidic limescale remover on cement grout — Acid slowly dissolves the cement, weakening the joint.
- Cleaning grout that's actually failing — If it's cracked, crumbling or missing, water is getting behind the tiles. That needs raking out and re-grouting.
- Skipping the sealer — Unsealed grout re-absorbs dirt almost immediately and you repeat the whole job next season.
Questions people ask
Why is my shower grout black?
Almost always mould, feeding on soap residue in a permanently damp joint. Clean it with a bleach solution and then improve the ventilation — a shower room that dries out within an hour rarely grows mould.
Can I paint or re-colour grout?
Yes. Grout pens and grout paint work and last a reasonable time on walls. On floors, foot traffic wears them faster. Both need the grout to be clean, dry and structurally sound first.
How often should grout be sealed?
Roughly annually in a shower, every two to three years elsewhere. Test it by dripping water on it: if it darkens and soaks in rather than beading, the seal has gone.