How to Treat and Prevent Mould Before Repainting Walls in Australia

Mould on walls is a common problem in Australian homes, especially in areas with high humidity, poor ventilation, or water leaks. Not only can mould damage your walls, but it can also affect your health, causing allergies, asthma, or respiratory issues.

If you’re planning to repaint your walls, addressing mould first is essential. Painting over mould without proper treatment will cause the paint to peel, bubble, or discolour, and the mould will likely return.

In this guide, we’ll show you how to treat mould effectively and prevent it from returning, so your repainted walls look flawless and last longer.

Why Mould Can Ruin Your Repaint

Mould thrives in damp, warm, and poorly ventilated areas. Painting over mould is a common mistake that leads to:

• Paint peeling or bubbling soon after application

• Stains bleeding through new paint

• Uneven finish or discolouration

• Recurring mould problems

Before repainting, it’s crucial to eliminate the mould and fix the underlying moisture issue.

Step 1: Identify the Mould

Before repainting, check for:

• Surface mould – Patches on paint or plaster (black, green, or white).

• Penetrating mould – Grows inside walls, drywall, or timber from persistent moisture.

Pro Tip: If mould covers more than 10 square metres, call a professional. Large infestations or structural mould require expert treatment before repainting.

Step 2: Protect Yourself

Mould spores can irritate your eyes, skin, and lungs. Always wear:

• Gloves

• Goggles

• A mask (P2 or N95 recommended)

Ensure the area is well-ventilated while cleaning, especially if you plan to repaint immediately afterward.

Step 3: Treat the Mould

To prepare walls for repainting, the mould must be completely removed.

Option 1: Mild Cleaning Solution

• Mix one cup of water with one cup of white vinegar or 1 tablespoon of detergent in a litre of water.

• Scrub the affected wall using a sponge or brush.

• Rinse with clean water and dry thoroughly.

Option 2: Bleach Solution (for heavy mould)

• Mix 1 part bleach with 3 parts water.

• Apply carefully to the mouldy area.

• Leave for 10–15 minutes, scrub, then rinse with water.

Important: Never mix bleach with ammonia or other cleaners—it produces toxic fumes.

Step 4: Dry and Ventilate Before Repainting

After cleaning, dry the walls completely. Use:

• Fans or heaters

• Open windows for ventilation

• Dehumidifiers in humid rooms

Moisture left behind will prevent primer and paint from adhering properly.

Step 5: Repair and Prime Walls

Before repainting:

1. Repair damaged areas – Fill holes, cracks, or flaking plaster. Sand smooth.

2. Apply a primer – Use a stain-blocking or mould-resistant primer. Priming prevents stains and provides a smooth base for paint.

👉 Pro Tip: For areas prone to moisture, use anti-microbial or mould-resistant paint for extra protection.

Step 6: Repaint Safely

Once the walls are dry, repaired, and primed:

• Apply paint in thin, even coats

• Use high-quality brushes or rollers for smooth coverage

• Allow proper drying time between coats

Following this process ensures your repaint is long-lasting and mould-free.

Step 7: Prevent Mould After Repainting

Even after repainting, prevention is key:

• Fix leaks and damp areas promptly

• Improve ventilation in bathrooms, kitchens, and laundry rooms

• Use dehumidifiers in humid climates or coastal areas

• Regularly inspect walls for signs of moisture

Common Mistakes to Avoid

• Painting over mould – Traps spores behind paint, causing failure.

• Skipping primer – Stains may bleed through, and paint won’t adhere well.

• Ignoring ventilation – Leads to condensation and new mould growth.

• Not drying walls fully – Moisture prevents proper adhesion.

For more official guidance on safely handling mould and preventing it in your home, you can refer to the NSW Government’s guide on mould in the home.

When to Call a Professional

• Mould covers large areas (>10 square metres)

• Mould is inside walls or ceilings

• Persistent mould despite cleaning and moisture control

Professionals can safely remove mould, repair surfaces, and recommend the best paint products for long-term protection.

Final Thoughts

If you want your repainted walls to look flawless and last, treating and preventing mould is non-negotiable. The key steps are:

1. Identify the source of moisture

2. Protect yourself while cleaning mould

3. Treat mould with vinegar, detergent, or bleach solutions

4. Dry and ventilate the area thoroughly

5. Repair, prime, and repaint

6. Maintain walls to prevent mould recurrence

By following this process, your walls will be healthy, clean, and beautifully repainted.

Before you repaint your walls, treating mould is only part of the process. Proper surface preparation is essential to ensure your new paint adheres well and lasts longer.

For a detailed, step-by-step guide on how to get your walls, weatherboards, decks, and fences ready for painting, check out our How to Prepare Surfaces Before Painting: A Complete Step-by-Step Guide. Following these preparation tips along with mould treatment will give you a professional, long-lasting finish.

At Board & Brush Experts, we know that treating and preventing mould is essential before any repainting project. Our team can help remove mould, prepare surfaces, and repaint your walls, weatherboards, decks, and fences for a long-lasting, flawless finish. Don’t let mould compromise your home—contact us today for expert advice and professional services to keep your home healthy and beautifully painted.