Painting an En-Suite Bathroom in a London Flat: Moisture, Mould, and the Right Paints

Painting an En-Suite Bathroom in a London Flat: Getting It Right

En-suite bathrooms in London flats are almost universally small, often poorly ventilated, and subjected to considerable daily moisture loading. A shower run for ten minutes in a room with no external window can raise the relative humidity to close to 100 percent. If the decoration is not specified and applied correctly, the consequences are predictable: peeling paint, dark mould growth around tiles and ceilings, and the need to redecorate within two or three years.

Getting the decoration right in an en-suite is not complicated, but it requires a clear-eyed choice of products, proper attention to preparation, and — critically — an honest assessment of whether the ventilation is adequate for the level of moisture the room generates.

The Ventilation Question First

Before choosing paints or discussing finishes, it is worth being direct about ventilation: if an en-suite does not have adequate extraction, no paint will fully solve the problem. Mould grows where moisture condenses on cold surfaces repeatedly. If the bathroom walls and ceiling are regularly reaching dew point temperature — which happens readily on cold plaster or plasterboard in an unheated or under-ventilated bathroom — mould will eventually establish itself regardless of what is painted on the walls.

For en-suites in London flats:

An extractor fan is the minimum requirement. Building Regulations require mechanical extraction in internal bathrooms (those without openable windows). The fan should be of adequate capacity for the room — typically 15 litres per second for a bathroom — and should ideally be connected to the light switch with a run-on timer so that it continues to operate for 15 to 20 minutes after the room is vacated.

Intermittent fans vs continuous low-rate ventilation. Modern best practice favours continuous low-rate fans (such as those from Vent-Axia or Nuaire's MEV systems) rather than simple on/off intermittent fans, because they prevent condensation from establishing in the first place rather than reacting to it. If a flat has a persistent mould problem in the bathroom, upgrading the fan is often the most effective intervention.

Opening the door after showering. In the absence of better mechanical ventilation, simply leaving the bathroom door open after a shower allows humid air to dissipate into the larger flat volume, reducing condensation on cold surfaces.

If the ventilation is genuinely adequate, the right paint will perform well. If it is not, even the best moisture-resistant paint will eventually struggle.

Choosing the Right Paint

The distinction between standard emulsion and moisture-resistant or bathroom-specific paint is meaningful, not just marketing. Here is what to look for:

Fungicide content. Good bathroom paints contain built-in biocides that inhibit the growth of mould and mildew on the paint surface itself. Note that this is not the same as preventing mould behind the paint — it only protects the surface. Common fungicidal agents include isothiazolinone compounds and zinc pyrithione.

Higher sheen levels. Matt emulsions are highly porous — moisture is absorbed into the paint film and provides an excellent medium for mould spores to germinate. A bathroom emulsion, silk emulsion, or satinwood finish has a higher sheen level that makes the surface more moisture-resistant and easier to wipe clean. We typically recommend a silk emulsion for bathroom walls and a satinwood or eggshell for any woodwork.

Specific bathroom and kitchen formulations. Dulux Bathroom+ and Crown Breatheasy Bathroom are both good-quality consumer products with adequate fungicide content and moisture resistance. For higher-end projects, Farrow & Ball's Modern Emulsion (their durable, wipeable formulation) performs well in bathrooms; it is not marketed specifically as a bathroom paint but has good moisture resistance and their full colour range is available in it.

Avoiding standard matt emulsion. Standard trade or retail matt emulsion on bathroom walls and ceilings is the single most common mistake we see in London flat bathrooms. It absorbs moisture readily and provides an almost ideal growing medium for mould. Even if it is applied with care and looks excellent initially, it will fail in a heavily used en-suite within a year or two.

Ceiling Specification

The ceiling is the most vulnerable surface in an en-suite. Hot, humid air rises; condensation forms on the coldest part of the room; and in many London flats, the ceiling is the least well-insulated surface. Dark mould patches on bathroom ceilings are among the most common complaints we receive.

For bathroom ceilings:

• Use a specialist bathroom ceiling paint or a silk/soft sheen emulsion with fungicide content — never a flat matt
• Apply a mould-resistant primer first if there is any history of mould in the room
• If mould has been present previously, treat the ceiling with a dilute bleach solution (one part bleach to four parts water), allow to dry completely, apply a stain-blocking primer to prevent bleed-through, and then the finish coat

The ceiling paint should ideally be a different formulation from the wall paint — moisture resistance is even more important at ceiling level than on the walls.

Preparing Bathroom Surfaces Before Painting

In any London flat, the surfaces in an en-suite bathroom are likely to include plasterboard walls (sometimes with render), plaster, existing tiles, and various joinery elements. The preparation requirements differ for each:

Plaster and plasterboard walls. Any existing mould should be treated and killed before decoration begins. Fill any cracks with a flexible, waterproof filler. Sand smooth and apply a mould-resistant primer before topcoats. In particularly damp rooms, a tanking slurry on the lower section of walls behind the shower area (if not already tiled) prevents moisture ingress at the most vulnerable zone.

Existing painted surfaces. If the existing paint is sound, clean it thoroughly, degrease, and abrade lightly before applying the new finish. If the existing paint is flaking or peeling, the failing material must be removed before repainting — applying new paint over peeling old paint is a temporary fix that will fail quickly.

Around tiles. The junction between tile and painted wall is a vulnerable point. Remove any failing grout or silicone sealant, regrout where needed, and ensure the painted surface meets the tiles cleanly. Fresh silicone sealant at tile-to-wall junctions is worth doing at the same time as redecoration.

Woodwork. Bathroom joinery — door frames, skirting boards, window boards if present — should be painted with a water-based eggshell or satinwood rather than a standard oil-based gloss. Modern water-based gloss finishes are more moisture-resistant than older formulations and do not yellow over time the way oil-based gloss does.

Colour Choices in Small En-Suites

Small en-suite bathrooms in London flats benefit from a considered approach to colour. The conventional advice to "keep small rooms pale" holds some truth, but very bright white can make a tiny bathroom feel clinical rather than calming.

Popular approaches for London flat bathrooms:

• Pale sage and dusty greens — these have become very popular in the past five years and work well in bathrooms. Farrow & Ball's Mizzle or Purbeck Stone, Little Greene's Aquamarine Light or Aged Ivory
• Warm white with a green or yellow undertone — Farrow & Ball's Pointing is a perennial choice for bathrooms; warm enough to avoid clinical coldness, light enough to feel fresh
• Deep colours for drama — in an en-suite where natural light is not a priority, a deep navy, dark slate, or forest green used on all four walls and the ceiling (a "fifth wall" approach) can create a genuinely luxurious atmosphere. These work particularly well in small rooms

Avoid very cool blues and greys in bathrooms with no natural light — they tend to read as cold and unwelcoming rather than calm.

If you are planning a bathroom redecoration in a London flat and would like expert advice on products and colour, we are always happy to help.