How to Deal with Mould on Walls Before Painting

Mould on walls is a common problem in Melbourne homes, particularly in bathrooms, laundries, south-facing rooms and older properties with limited ventilation. If you are planning to repaint, dealing with mould properly before the first coat goes on is essential. Painting over mould without treatment will not solve the problem. It will simply hide it temporarily before it grows back through the new paint.

Why Mould Grows on Walls

Mould needs three things to thrive: moisture, warmth and an organic food source. In Melbourne, the combination of humid winters, overnight condensation and older homes with poor ventilation creates ideal conditions. Mould commonly appears on bathroom ceilings, around window frames, behind furniture placed against external walls and in rooms that receive little airflow.

Understanding why the mould appeared is just as important as removing it. If the underlying moisture issue is not addressed, the mould will return regardless of how well the walls are prepared and painted.

Step 1: Identify and Fix the Moisture Source

Before any painting work begins, identify what is causing the moisture. Common causes in Melbourne homes include:

• Poor bathroom ventilation or a non-functioning exhaust fan
• Leaking roofs, gutters or downpipes allowing water into wall cavities
• Rising damp in older homes without adequate damp-proof courses
• Condensation on cold walls in rooms without heating or airflow
• Blocked weep holes in brick veneer construction

A professional painter will assess the extent of mould and may recommend addressing the moisture source before starting. There is no point investing in a quality paint job if the underlying problem will cause mould to return within months.

Step 2: Remove the Mould

For surface mould on painted walls, a solution of one part household bleach to four parts water is effective. Apply with a sponge or spray bottle, leave for fifteen minutes, then wipe clean and allow the wall to dry completely. For larger areas or persistent mould, a commercial mould removal product designed for interior use may be more appropriate.

Always wear gloves, eye protection and a mask when treating mould. Work in a well-ventilated area and protect floors and furnishings from bleach splashes.

For severe mould that has penetrated into plaster or timber, the affected material may need to be cut out and replaced. This is particularly common in bathrooms where water has been leaking behind tiles or in subfloor areas with rising damp. A professional painter or builder can assess whether removal and replacement is necessary.

Step 3: Prepare the Surface

Once the mould is removed and the wall is completely dry, sand the area lightly to remove any remaining staining and create a smooth surface. Wipe down with a damp cloth to remove dust, then allow to dry again.

Apply a mould-resistant primer or sealer before painting. Products like Zinsser Mould Killing Primer or Dulux Prepcoat Sealer Binder are designed to seal residual staining and provide a base that inhibits future mould growth. This step is critical and should not be skipped, even if the wall looks clean after treatment.

Step 4: Paint with Mould-Resistant Products

For rooms prone to moisture and mould, use a paint specifically formulated for wet areas. Most major Australian paint brands offer kitchen and bathroom paints with built-in mould inhibitors. These paints are typically available in low-sheen or semi-gloss finishes, which also makes them easier to clean.

In Melbourne, professional painters will often recommend a semi-gloss finish for bathroom and laundry ceilings where condensation is heaviest, and a low-sheen or satin finish for walls. The smoother the finish, the harder it is for mould spores to take hold.

Prevention After Painting

A fresh coat of mould-resistant paint is only part of the solution. To keep mould from returning:

• Run exhaust fans during and for at least twenty minutes after showers
• Open windows regularly to allow airflow, even in winter
• Keep furniture slightly away from external walls to allow air circulation
• Fix any leaks or drainage issues promptly
• Consider a dehumidifier in particularly damp rooms

When to Call a Professional

If mould covers a large area, keeps returning despite treatment, or is accompanied by musty smells in wall cavities, it is worth getting a professional assessment. Melbourne painters experienced with mould remediation can evaluate the scope of the problem, treat it properly and apply the right products to give you a lasting result.

Eagle Painting regularly helps Melbourne homeowners deal with mould-affected walls as part of interior repainting projects. Contact us for a free assessment and quote.