How to Clean Mould from Grout & Silicone (Showers, Bathrooms & Kitchens)

Why mould forms on grout and silicone

Mould needs two things: moisture and a food source. In bathrooms and kitchens, moisture is obvious (steam, splashes, condensation). The “food” is usually the film you can’t easily see: soap scum, shampoo residue, skin oils, grease and limescale deposits. Grout is porous, so it traps grime and stays damp longer. Silicone is non-porous, but the surface still collects residue, and if water finds its way behind lifting sealant, mould can thrive out of sight.

That’s why a lot of people spray a mould remover, rinse it off quickly, and see only temporary improvement. Contact time and prep matter, and silicone in particular has a “point of no return” where cleaning won’t fully remove the black shadowing because the mould has penetrated the sealant.

Safety first (especially with bleach-based cleaners)

Many mould treatments are effective because they are chemically aggressive. Treat this like a proper cleaning job, not a quick wipe.

• Ventilation: open a window, run the extractor fan, keep the door open.
• Protection: wear rubber/nitrile gloves; consider eye protection; if you’re sensitive or the mould is heavy, add an FFP2/FFP3 mask.
• Never mix products: bleach mixed with vinegar or other acids can release toxic chlorine gas. Bleach mixed with ammonia is also dangerous.
• Test first: if you have coloured grout, painted surfaces, or natural stone tiles, test any product on an inconspicuous area.

Before you treat mould: remove the soap scum (the step most people skip)

If you treat mould on top of a greasy film, the cleaner struggles to reach the problem. This “invisible layer” is why mould returns so quickly.

1. Spray the area with a general bathroom cleaner/degreaser (or use warm water with a small amount of washing-up liquid).
2. Scrub gently with a nylon brush or old toothbrush to break up residue, especially at corners and along silicone edges.
3. Rinse thoroughly and wipe dry with a clean cloth.

Once the surface film is gone, your mould treatment has a much better chance of lifting staining and killing what’s left behind.

Grout vs silicone: how to tell what will actually clean up

Grout

Grout is porous, so mould can be both a surface issue and a staining issue. Most grout responds well to peroxide or oxygen bleach methods, with bleach gel reserved for stubborn black staining.

Silicone

Silicone is trickier. If the mould is only on the surface (often mixed with soap scum), it can usually be cleaned. If the mould has penetrated the sealant or is growing behind it due to water ingress, cleaning may improve it but won’t fully remove the shadowing for long.

Quick indicator: if you’ve cleaned properly (with contact time) and the silicone still has grey/black “ghosting” that looks like it’s inside the bead, it’s usually time to remove and replace the silicone.

Method 1: Hydrogen peroxide (great all-rounder for grout and surface mould)

Hydrogen peroxide (commonly 3%) is a strong option for mould and staining without the heavy bleach smell. It’s often a great first choice for regular maintenance and moderate mould patches.

How to use it on grout

1. Apply peroxide generously to the grout lines (spray bottle, or soak cotton pads/kitchen roll and press onto the grout).
2. Leave for 10–20 minutes so it can work.
3. Scrub with a grout brush or toothbrush.
4. Rinse well and dry the area thoroughly.

If you see improvement but not a complete lift, repeat once more. Two sensible passes are usually better than one harsh blast with something stronger.

Method 2: Oxygen bleach paste (excellent for deep grout staining)

Oxygen bleach (often sold as sodium percarbonate-based cleaners) is very effective on porous grout where staining has sunk in. It’s a strong method without the chlorine bleach fumes, and it’s particularly useful when mould is mixed with deep-set grime.

How to use oxygen bleach on grout

1. Mix oxygen bleach powder with warm water to form a thick paste (think “spreadable”, not runny).
2. Apply along grout lines so the paste sits on top rather than dripping away.
3. Leave for 20–60 minutes. If it dries out too quickly, lightly mist it so it stays active.
4. Scrub, rinse thoroughly, and dry.

This method is often the best balance of results and comfort if you dislike the smell and harshness of bleach.

Method 3: Bleach gel (fast, powerful, but use carefully)

Bleach gel can be extremely effective for heavy black mould on grout because it clings and stays in place. It’s also the easiest method to overuse. If you rely on bleach constantly, it can contribute to grout deterioration over time and may lighten coloured grout.

How to use bleach gel on grout

1. Apply a thick line of bleach gel directly onto the grout.
2. Leave for 10–30 minutes (follow the product label).
3. Scrub gently, rinse very thoroughly, and dry.

Important: avoid bleach products on or near natural stone (marble, limestone, travertine) unless the product specifically states it is safe for stone.

Cleaning mould on silicone sealant (what works and what doesn’t)

For silicone, the most effective technique is to keep the active cleaner in contact with the sealant long enough to work. Spraying and rinsing immediately rarely shifts the black specks in corners.

The “soaked tissue wrap” method (best for surface mould)

1. Cut strips of kitchen roll or use cotton pads.
2. Soak them with either hydrogen peroxide or a bleach-based cleaner (choose one method; don’t mix products).
3. Press the soaked strips firmly onto the silicone bead so the sealant is fully covered.
4. Leave for 30–90 minutes (peroxide usually needs longer; bleach often works faster).
5. Remove, scrub gently with a toothbrush, then rinse and dry.

If the silicone improves dramatically, you likely had surface mould and grime. If it barely changes or the black “shadow” remains inside the bead, the sealant is probably stained through or mould is behind it.

Using a Steam Cleaner to Remove Mould from Grout and Silicone

A steam cleaner can be a brilliant tool in the fight against mouldy grout and grimy silicone, but it’s best used as a deep-cleaning stage rather than the only solution. Steam excels at loosening soap scum, body oils and embedded dirt — the exact residue mould feeds on — and that makes any follow-up treatment far more effective.

When steam cleaning works best

Steam is most useful when your grout looks dark because it’s dirty as well as mouldy, and when silicone has a slick film that cleaners struggle to penetrate. It can also be a good choice if you want to reduce how often you use harsh chemicals, because it shifts the grime mechanically before you treat the mould.

How to steam clean grout and silicone properly

Use a detail nozzle or small brush attachment and work in short, controlled passes. Hold the head just off the surface and move steadily along the grout lines. You want enough heat to loosen residue, but not so long that you create heavy condensation that keeps the area damp.

On silicone, steam is best used to break down surface film. Wipe immediately with a microfibre cloth while the area is warm, then rinse and dry. If you’re using a mould treatment afterwards, steaming first is ideal because it removes the barrier of soap scum and helps the active ingredient reach the mould.

What to avoid with steam

Be cautious if grout is cracked, loose or sandy, as aggressive brushing combined with heat can worsen weak grout. Also take care if silicone is lifting at the edges — steam and moisture can encourage water to creep behind the sealant, which is exactly where persistent mould thrives. If you have natural stone tiles, test first and avoid overly abrasive attachments.

Best workflow: steam to strip residue, then treat the mould (peroxide/oxygen bleach on grout; soaked tissue method on silicone), then rinse and dry thoroughly.

When cleaning won’t fix it: remove and replace mouldy silicone

If silicone has black staining that won’t shift after two proper attempts (with contact time), cleaning is usually temporary at best. Replacing sealant is often the only way to get a truly clean, long-lasting finish.

Signs you should re-seal

• The silicone has dark shadowing that looks like it is inside the bead.
• The sealant is peeling, split, lifting, or has gaps at the edges.
• Mould returns within days even after thorough cleaning and drying.
• You suspect water is getting behind the sealant (damp patches, musty smell, persistent wetness).

High-level re-sealing steps (shower tray, bath edge, kitchen worktop)

1. Cut and remove the old silicone with a sealant remover tool or sharp blade (work carefully to avoid scratching).
2. Remove residue (a silicone remover gel can help), then clean the surface thoroughly.
3. Disinfect the area and let it dry completely before applying new sealant.
4. Apply a quality sanitary (anti-mould) silicone in a smooth, continuous bead.
5. Tool the bead neatly and allow full cure time before heavy water exposure.

Done properly, re-sealing is one of the biggest “visual upgrades” you can make to a bathroom in an afternoon.

How to stop mould coming back (the part that makes cleaning last)

Even the best mould removal method won’t last if moisture and residue keep building up. Prevention isn’t complicated, but it needs consistency.

Dry the area quickly after use

Run your extractor fan during showers and for at least 20 minutes after. If ventilation is weak, crack a window for a short time to clear humidity. A quick wipe-down or squeegee on tiles and shower screens removes the water film that feeds mould.

Reduce the “food source”

Soap scum and shampoo residue are mould-friendly. A weekly clean that focuses on the silicone edge and grout lines will dramatically slow regrowth. You don’t always need a harsh mould killer; removing residue regularly is often enough to prevent black spotting.

Check for small failures

If one corner constantly goes mouldy, look closely for cracked grout, failed silicone, or tiny gaps that let water sit where it shouldn’t. Persistent damp behind sealant is a re-seal job, not a cleaning job.

Consider sealing grout in wet areas

A grout sealer can reduce absorption and staining, making future cleaning easier. It won’t make grout waterproof, but it helps prevent moisture and grime from sinking in so quickly, especially in shower enclosures.

Common mistakes that waste time

Most disappointing results come down to one of these issues:

• No contact time: spraying and rinsing immediately doesn’t give the product time to work.
• Skipping degreasing: cleaners can’t penetrate soap film properly.
• Over-scrubbing silicone: it can roughen the surface and make future staining worse.
• Not drying after rinsing: leaving wet grout and silicone encourages faster regrowth.
• Using bleach for everything: it can be effective, but it’s not always the best long-term approach, especially for frequent use.

When to Regrout (and when cleaning won’t be enough)

Cleaning mould from grout works well when the problem is mainly on the surface or lightly stained into the grout. But grout is porous and it also wears down over time. If the grout is damaged, constantly damp, or breaking up, mould will keep returning because moisture is getting in and the grout can’t properly dry out. In those cases, regrouting is usually the better long-term fix.

Signs you should regrout instead of repeatedly cleaning

• Cracking or missing grout: gaps, hairline cracks, or sections that have fallen out between tiles.
• Crumbling or sandy grout: the grout powders when you rub it, or it flakes away when brushed.
• Deep staining that won’t lift: after two thorough cleans (with proper contact time), grout still looks permanently dark.
• Persistent mould in the same area: mould returns quickly in one corner even after cleaning, drying, and improving ventilation.
• Grout stays damp: the area feels wet for hours after use, suggesting water is soaking in or sitting behind the surface.
• Loose or hollow-sounding tiles: this can indicate moisture issues behind the tiles (this is beyond a simple regrout).

When regrouting is not the only issue

If tiles are loose, the wall sounds hollow, or water is clearly getting behind the tiles, regrouting alone may be a temporary cosmetic fix. That usually points to a bigger moisture problem (failed sealant, movement, or water ingress). Fixing the cause first prevents mould and staining coming straight back.

Quick rule of thumb

Clean if grout is intact and mould is mainly staining. Regrout if grout is cracked, missing, crumbling, or repeatedly goes mouldy in the same spots despite proper cleaning and drying.

If you do regrout in a shower or around a bath, consider finishing with a grout sealer once fully cured to help reduce future moisture absorption and make routine cleaning easier.

FAQ

Will vinegar remove mould from grout and silicone?

Vinegar can help with some surface mould and is useful on limescale, but it’s not always strong enough for established black mould in bathrooms. Most importantly, never use vinegar after bleach unless you have rinsed extremely well and allowed the area to air out. Don’t mix products.

Why does silicone stay black even after cleaning?

Usually because mould has penetrated the silicone or is growing behind it. In that case, cleaning might lighten it temporarily, but replacement is the proper fix.

How long should I leave mould remover on?

It depends on the product, but generally peroxide needs around 10–30 minutes on grout (often longer for the silicone wrap method), oxygen bleach paste can sit for 20–60 minutes, and bleach gel commonly works in 10–30 minutes. Always follow the label and rinse thoroughly.

Can I steam clean mould without chemicals?

Steam can loosen grime and reduce surface contamination, but mould often returns if moisture and residue remain. For best results, use steam to remove soap scum and dirt first, then follow with a targeted treatment and dry thoroughly.