How professionals remove mould from bathrooms — and keep it away

How professionals remove bathroom mould — and keep it away: step-by-step, kit and one lasting fix

There’s a moment you dread: pulling back the shower curtain to find black speckles creeping along the grout, the silicone edge turning grey, and a musty smell that never quite dissipates. You scrub, it fades, then returns within a week. Many people don’t realise that bathroom mould is as much a moisture-management problem as it is a cleaning one.

Professionals approach it very differently. They don’t just kill what’s visible; they track the moisture, treat the spores you can’t see, and make the room dry faster than mould can regrow. Here’s exactly how they do it — and how you can copy the parts that matter.

What mould needs to thrive

Mould isn’t mysterious. It needs persistent moisture, a bit of warmth, and a food source. Bathrooms provide all three in spades: steam condenses on cool tile and paint, soap scum and body oils form a thin biofilm, and poor ventilation keeps relative humidity high for hours after each shower.

The glass test is telling. If your mirror steams for 15 minutes or more, humidity is trapped. If grout stays dark long after you’ve turned off the water, moisture is being absorbed or has nowhere to go. Removing mould starts with removing that damp window of opportunity.

The professional removal method, step by step

Inspection and containment

Pros start by finding the moisture source. They look for failed extractor fans, ducts that vent into lofts rather than outdoors, leaking shower valves, cracked grout lines and perished silicone. A cheap hygrometer confirms whether the room sits above 60% relative humidity after bathing — the level at which mould is most comfortable.

Containment matters. A bathroom door is kept closed, soft furnishings are removed, and if growth is extensive, professionals set up a negative-air machine with a HEPA filter. For small jobs at home, open a window, shut the door, and wear gloves, eye protection and a proper mask (a P2/P3 or FFP2/3 filter). Disturbing mould sends spores airborne; the gear prevents you from inhaling them or getting chemicals in your eyes.

Surface preparation

It’s counterintuitive, but wetting mould before you clean reduces airborne spores. Pros lightly mist the area with water, then pre-clean with a detergent to strip soap film. Many people skip this step and wonder why biocides fail. A greasy biofilm acts like a raincoat, stopping the chemistry from meeting the mould.

Tiles, glass and enamel are non-porous and respond well to this rinse. Grout and unsealed stone are porous; professionals avoid saturating them during pre-clean to keep the colony from retreating deeper.

Targeted treatment

Here’s where products and patience matter. Professionals pick a mould-killing agent, apply generously, and give it time to work. Dwell time — typically 10 to 15 minutes, longer on stubborn patches — is what actually kills spores and breaks down staining. Agitation with a soft brush helps the chemistry reach the roots, especially in grout lines.

On silicone that has turned peppered grey, they rarely attempt heroics. Silicone is flexible and absorbent; once mould is embedded, the stain often persists even when the organism is dead. Pros cut it out with a sharp blade, clean the joint, let it dry thoroughly, and reseal with a sanitary-grade, mould-resistant silicone. It looks better and lasts.

Rinse and neutralise

After treatment, surfaces are rinsed or wiped with clean water to remove chemical residues and dead growth. This is the point at which a proper HEPA vacuum is useful. Professionals vacuum the surrounding area to capture spores that settled during cleaning, then wipe surfaces with a microfibre cloth. If bleach-based products were used, they don’t mix them with anything acidic during the same session. Bleach and vinegar together release chlorine gas — dangerous in a small bathroom.

Drying and verification

The last step is drying the room quickly and completely. Professionals run an extractor or dehumidifier, use fans to move air across wet surfaces, and crack doors and windows to create cross-ventilation. Within two to four hours, the space should be dry to the touch and humidity back below 55%. A return visit a week later confirms no new spotting.

Products the pros trust — and when to use them

There isn’t a single miracle product; the best choice depends on the surface and the job.

Hydrogen peroxide, typically at 3–6%, is a favourite because it’s effective on porous surfaces and doesn’t leave chloride residues. It breaks down into water and oxygen, which is helpful in small, unventilated rooms. It needs decent dwell time and can temporarily lighten some materials, so spot testing is wise.

Chlorine bleach (sodium hypochlorite), usually diluted to around 1:10 with water, excels at whitening stained grout and killing surface mould on glazed tile. It’s fast and visible. But it can pit metals, fade textiles and damage natural stone, and fumes are not friendly in a tight space. Professionals use it with care and ventilation, and never mix it with vinegar or ammonia-based cleaners.

Quaternary ammonium compounds (often listed as benzalkonium chloride) are common in mould sprays because they linger, helping to suppress regrowth on non-porous surfaces. They’re less effective on deeply porous materials. Pros might use a quat-based cleaner after a peroxide treatment as a residual barrier in high-risk areas.

Understanding limescale helps too. What looks like mould on glass shower screens is often mineral scale harbouring bacteria and soap scum. Treat scale with a mild acid cleaner first, then address any organic growth. Removing the scale deprives future mould of a foothold.

Drying, not just cleaning

Ask a restorer what prevents mould and you’ll hear one mantra: keep the room dry. That means reducing moisture at the source and boosting ventilation long enough after every shower.

A correctly sized extractor fan is non-negotiable. In practical terms, look for around 15 to 30 litres per second of airflow in a bathroom, ducted to the outside, not just into a loft. A run-on timer keeps it going for 20 to 30 minutes after you finish bathing. If the fan is loud, people turn it off; quieter, higher-quality models get used and make the difference.

Airflow into the room matters as much as airflow out. A 10–15 mm gap under the bathroom door allows make-up air to replace what the fan removes. Without it, the fan starves and humidity lingers despite the noise.

How to keep it away

Daily habits, not harsh chemicals, do the heavy lifting. A quick squeegee of walls and glass strips a surprising amount of water, cutting drying time dramatically. Leaving the shower door or curtain fully open, not bunched, exposes damp surfaces to air. Towels and bath mats should be hung to dry on heated rails rather than left in a heap, which can push room humidity into the mould-friendly zone for hours.

Weekly, a wipe-down with a gentle bathroom cleaner or dilute peroxide prevents biofilm build-up. Grout benefits from an occasional scrub with a soft brush; think maintenance, not battle. If you have persistent problems in one corner, a small, quiet dehumidifier on a short timer can be transformative, especially in windowless internal bathrooms.

Materials choices help. Epoxy grout resists staining far better than cement-based grout and doesn’t absorb moisture the same way. High-quality, sanitary-grade silicone with fungicide resists colonisation longer. On painted walls and ceilings, a moisture-resistant, scrubbable paint designed for kitchens and bathrooms copes better with regular condensation.

Many people don’t realise that shower temperature and duration play a role. Very hot, very long showers push humidity up sharply. Turning down a notch and finishing with a 30–60 second burst of cooler water reduces steam and leaves less moisture to remove.

When to replace and when to call a specialist

If mould is limited to surface spots on tile and grout, a careful clean and improved ventilation usually solves it. But if you see widespread growth on painted plasterboard, persistent odour despite cleaning, or mottling that returns within days, there may be moisture inside the wall. Leaking pipes, failed tanking behind a shower, or gaps around a bath can feed hidden mould you can’t reach with sprays.

At that point, professionals will remove and replace affected materials, fix the leak, and dry the cavity thoroughly before finishing. They may deploy moisture meters to find wet zones or use an infrared camera to spot cold bridges where condensation forms behind the paint. It sounds involved, but it’s often quicker and cheaper than endless surface cleaning.

One small habit that makes the biggest difference

“If you can smell it after a shower, humidity is still trapped.” The single habit that separates mould-free bathrooms from mouldy ones is letting the extractor run long enough. Make it automatic with a run-on timer, leave the door ajar after you leave, and use a simple hygrometer to learn how long it takes for your room to drop below 55% relative humidity. The cleaning then becomes occasional care, not a constant fight.

Professional results aren’t about stronger chemicals; they’re about process. Clean the biofilm, choose the right agent, respect dwell time, and dry thoroughly. Fix airflow and materials, and mould doesn’t have a chance to come back.