Unless you deliberately chose a dark colour, you should be concerned if your grout lines look black. This usually indicates mould or mildew growth, which is hazardous to your health.
You can prevent this from happening, but things can happen despite our best efforts! If you’ve noticed dark grout stains, then you just have to clean them up.
How to clean grout that has turned black? You can use one of these grout cleaners:
And, of course, remember to use the appropriate cleaning supplies and wear protective equipment!
What Causes Grout to Turn Black?
The primary causes of black grout are mould and mildew.
Most households use cement-based grout for porcelain or ceramic tiles. This type of grout is porous and requires regular sealing to protect the material.
Otherwise, grout will absorb most substances it comes into contact with, such as water, soap, spores, and bacteria. But grout sealer can degrade over time, and it’s not 100% impermeable.
It’s difficult to get those same substances out of the grout, which creates a moist environment where bacteria and spores thrive. That leads to mould and mildew growing in the tile grout.
A poorly ventilated bathroom can also lead to mould, which causes black grout. Sometimes, though, this results in pink mould – which you can identify by orange grout stains on your shower walls or floor.
There’s always the chance your grout turned black for more innocuous reasons, like a certain little someone getting too enthusiastic with markers. In this case, you just need to let a magic eraser work its, well… magic!
How Often to Clean Grout
Tackle stained grout as soon as possible! The longer a stain sits, the more difficult it will be to remove.
Deep clean your grout at least once a month.
(If you don’t want to do all that scrubbing, though, just look up the most reliable home cleaners in your area!)
How to Clean Grout That Turned Black
These methods will work whether you’re trying to clean black mould in shower grout, kitchen grout, and other areas. As always, test your chosen cleaner on an inconspicuous spot first to make sure it doesn’t damage your tiles!
NOTE: Do not use these cleaning solutions on natural stone tiles, which require specialised products. You may wish to consult a professional in these cases.
Before cleaning black grout
Clean off any surface dirt from the tile grout before you tackle the black stains. This will ensure your cleaning solution is effectively targeting the grout stains and not any soap scum or other residue.
Always wear protective equipment when you clean grout, including:
- Rubber gloves
- Goggles or similar eye covers
- A face mask
It’s important to remember that you might not restore your white grout to its former pristine condition. Black stains from mould are difficult to remove completely, and you may need to recolour the grout after cleaning.
In the worst-case scenario, you may need to have your tiles completely re-grouted.
Clean black grout with white vinegar
NOTE: Do not use this on unsealed grout, as it can seep into the air spaces and weaken the grout as a whole.
Your first line of offence against blackened grout is good ol’ vinegar. Its acidic properties can kill mould, making it great for cleaning grout stains. It’s also good if you’re avoiding the use of harsh chemicals.
You can also use lemon juice as a substitute or additive to cut the vinegar scent.
Mix equal parts white vinegar and warm water in a spray bottle. Saturate the grout completely with the vinegar solution, then let it sit for 5–10 minutes.
Use a stiff brush (such as a nylon scrub brush) and a bit of elbow grease to start scrubbing the grout’s surface. If you’re working in a small area, an old toothbrush will work as well.
Rinse the area with clean water, then repeat with the vinegar grout cleaner as necessary.
Let the tiles and grout fully dry.
Clean black grout with baking soda and ammonia
NOTE: Before trying this grout cleaner, it’s important to remember that you can only mix ammonia with baking soda. It is incredibly dangerous to mix ammonia with vinegar or bleach.
This cleaning solution can tackle tougher stains when cleaning black grout.
Mix 7 cups of warm water, 1/2 cup baking soda, and 1/3 cup ammonia in a bucket.
Use a sponge or soft cloth to apply the cleaning solution to your grout lines. Let it sit for 10–20 minutes.
Take a scrub brush or old toothbrush to scrub the grout. If the black stains aren’t coming off easily, reapply the paste and wait another 30–60 minutes, then scrub again.
Rinse the paste off with clean water, then let the area dry completely.
Dispose of any leftover cleaner immediately.
Clean black grout with hydrogen peroxide
You can use hydrogen peroxide alone or in a paste with baking soda. It’s best for light-coloured or white grout since it has mild bleaching properties.
As a straight cleaner, mix equal parts 3% hydrogen peroxide and warm water in a spray bottle. Saturate the dirty grout with the cleaning solution, then let it sit for up to an hour.
As a cleaning paste, mix 1/2 cup baking soda with 1/4 cup hydrogen peroxide. You can recycle a squeeze bottle with a nozzle for easier application!
Spread the paste over the grout and let it sit for at least 5 minutes. Then use a stiff-bristled brush to scrub the grout until it’s clean.
Wipe away any residue with a sponge or paper towel, then rinse the grout. Repeat as needed until the stains have lifted.
Dispose of any leftover grout cleaner immediately.
Clean black grout with oxygen bleach
If the mould persists, or if you want to bring out the big guns, you can use oxygen bleach. (We like Koala Eco’s oxygenated bleach!)
It’s just as effective as the chlorine version, but is less reactive.
Still, take all safety precautions when using any form of bleach! Wear protective equipment and ensure the room is well-ventilated.
Follow the manufacturer’s instructions for diluting the bleach, and only mix it with water. It is extremely dangerous to mix bleach with anything else, such as vinegar.
Apply the bleach solution to the grout, then leave it for 15 minutes. If you notice the grout has absorbed all the mixture before time is up, add more!
After 15 minutes, use a stiff brush to scrub the grout. Rinse the tiles thoroughly afterwards (you can use a mop) then air out the room to dry.
Don’t worry if your grout doesn’t look completely clean right away – the compounds in bleach will work for up to 6 hours, even after you’ve rinsed the area.
How to Prevent Blackened Grout
Make sure you clean tile floors, walls, and grout at least once a week. This will prevent dirt and bacteria from building up – especially in your bathroom, where soap scum can be a breeding ground for mould spores.
You can also keep vinegar spray and a squeegee in the bathroom for quick post-shower clean-ups!
Keep all rooms well-ventilated to prevent moisture accumulation. For inner rooms with no access to windows (such as a powder room), install exhaust vents and leave doors open whenever possible.
Have your grout re-sealed every 6 months in high-traffic or high-use areas. If you notice that moisture is no longer beading up on the grout surface, that’s a sign it needs new sealant.
Alternatively, if you have the budget, you can opt for epoxy or acrylic-based grout. These types are waterproof and do not need sealing, but require a high upfront cost.
Still, it’s best to know how to clean grout that has turned black, as you never know when it’ll come in handy. Just check first to make sure the discolouration is due to mould or dirt and not someone forgetting to clean up some spilled hair dye – you don’t want to go all-out for nothing!