Expert Painters

Mould-Resistant Paint and Wet Areas: What It Can and Cannot Do

An expert person removing mould from a wall
09 Nov

Mould-resistant paint is one of the most misunderstood products on the shelf. It does not remove mould, it does not fix a damp wall, and painting it over a mouldy surface achieves nothing except hiding the problem until it comes back through.

What it does do is useful, but only as the last step in a sequence.

Why Melbourne homes grow mould in winter

Most interior mould here is not a leak. It is condensation.

Cold weather, heating running, windows shut, showers and cooking and drying clothes indoors. Warm moist air meets a cold external wall, the moisture condenses on the surface, and mould grows on it. That is why it appears in the same predictable places:

  • Bathroom and laundry ceilings, and the wall above the shower
  • South-facing external walls, which never get sun
  • Behind wardrobes and bedheads pushed against an external wall, where there is no airflow
  • Window reveals and around aluminium frames, which are cold bridges
  • Inside built-in robes on an external wall

Solid brick and uninsulated walls are worst, which covers a lot of inner Melbourne housing.

The order that actually works

Every step before the last one is the part people skip.

  • Find the moisture source. Condensation, a leak, rising damp or inadequate ventilation are four different problems with four different fixes
  • Fix it. This is usually ventilation rather than anything structural
  • Kill the mould properly and let the surface dry fully
  • Then, and only then, coat it with an appropriate system

Skip to step four and you are painting over a living organism on a wet substrate. It will be back within a season, often within weeks.

Bleach is not the answer people think it is

Household bleach removes the colour from mould. On a porous surface like plaster or render it does not reliably kill the structure growing into the material, and the water in it adds moisture to a wall that already has too much.

What works better is a proper fungicidal wash, applied and left to dwell for the time the product specifies rather than wiped straight off, then removed and the surface allowed to dry completely. On a painted surface where the mould is only on the film, that plus a thorough clean is often enough. Where it has gone into the plaster, the plaster may have to come out.

Our existing guide on getting rid of mould covers the removal side in more detail.

What mould-resistant paint actually does

These products carry a fungicide in the dried film that inhibits growth on the coating surface. That is a genuine benefit in a bathroom or a laundry, where humidity is unavoidable no matter how good the ventilation.

What it is not:

  • It is not a treatment. It does not kill what is already there
  • It is not a damp-proofing product and will not stop moisture moving through a wall
  • It is not permanent. The fungicide depletes over years
  • It is not a substitute for an exhaust fan

Used correctly, as the topcoat in a system on a wall that has been dried and treated, it extends the interval before regrowth considerably. Used as a shortcut, it buys a few months.

The exhaust fan question

This is the single most common cause of recurring bathroom mould in Melbourne, and it has nothing to do with paint.

A great many bathroom exhaust fans vent into the roof space rather than outside. The fan moves the moisture out of the bathroom, dumps it into the roof, and it condenses up there and comes back through the ceiling. The bathroom ceiling then grows mould no matter what is painted on it, and the roof framing quietly suffers.

If a bathroom ceiling keeps going mouldy after being treated and repainted, get someone into the roof space to check where the fan actually discharges. Fixing that solves the problem permanently in a way no coating will.

Specifying a wet area properly

For bathrooms, laundries and ensuites:

  • A moisture-resistant, washable finish rather than a standard flat wall paint
  • Low sheen or satin on walls, which cleans without burnishing. Full gloss shows every imperfection on a plaster wall
  • The ceiling matters more than the walls here, because it is the coldest surface and the one people forget
  • Seal around the shower, windows and penetrations before coating, not after
  • Allow proper curing before the room goes back into heavy use, which is harder in winter

Our guide to bathroom painting covers the preparation, and low-VOC products matter in a small unventilated room.

When it is not condensation

Two other causes need different answers.

If the mould is at the base of a wall with white crystalline deposits or crumbling plaster, that is moisture coming through the masonry rather than condensing on it. See our notes on efflorescence.

If it appeared suddenly in one patch, especially on a ceiling, look for a leak before assuming anything else. Our guide to water damage repaints covers the sequence.

Rentals

Mould is one of the most common disputes between tenants and landlords, and the argument usually turns on whether it is a ventilation and building problem or a lifestyle one.

From a painting perspective the useful contribution is documentation: photographs of the extent, a written scope separating treatment from repainting, and a plain statement of what we found behind it. Our guide to rental property painting covers the rest.

When to get someone else involved

Call a professional rather than a painter if the affected area is large, if it keeps returning after proper treatment, if anyone in the house has respiratory symptoms that improve when they leave, or if you suspect it is inside the wall cavity rather than on it. Those are building and health questions, not decorating ones.

What we do

  • Identify whether the cause is condensation, leak or rising damp before quoting
  • Fungicidal treatment and full drying before any coating
  • Mould-resistant systems in bathrooms, laundries and problem rooms
  • Plaster replacement where mould has gone into the sheet
  • Honest advice when the real fix is a fan or ventilation rather than paint

We are based in Richmond and work across Melbourne, the bayside suburbs and coastal Victoria.

Call 0404 330 332. If it is a bathroom ceiling that keeps coming back, check where the exhaust fan vents before you book anyone.

šŸ“ Our Service Areas Across Melbourne, the Mornington Peninsula, Surf Coast & Phillip Island

Melbourne & Bayside

Phillip Island & Bass Coast

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