How to Remove Mould from Walls and Keep It from Coming Back

Severe mould growth spreading across interior walls, a common sign of damp and poor ventilation in Australian homes

Mould on walls can creep in quietly, especially in humid conditions or areas with poor ventilation. Left unchecked, it can spread quickly, damaging your home and potentially affecting your health.

Here’s how to remove mould from walls safely and effectively, and most importantly, how to stop it from returning.

What Causes Mould on Walls

Mould thrives in damp, poorly ventilated conditions, and once it takes hold, it can be stubborn to get rid of. Common causes include:

• Condensation - with the warm, moist air meeting a cold wall can leave water droplets behind, creating the perfect breeding ground.

  
  

• Leaks – Water seeping from roofs, pipes, or gutters can keep walls damp and feed mould growth.

  
  

• Poor ventilation - Rooms with little airflow, such as bathrooms, basements, or laundry areas, often trap moisture.

  
  

• Flooding or water damage - Even after surfaces appear dry, moisture can remain in the walls.

  
  

• Structural issues - Cracks in walls or faulty seals around windows and doors can let water in.

  
  

By identifying what’s causing the dampness, you’re halfway to preventing mould from returning.

Why Mould on Walls Should Be Taken Seriously

Mould is more than just an eyesore. Damp, poorly ventilated walls create the perfect breeding ground for mould, which can:

• Trigger allergies, asthma, and respiratory irritation

  
  

• Cause headaches, sinus problems, and fatigue over time

  
  

• Damage paint, plaster, wallpaper, and even wall framing

  
  

• Hide signs of leaks or long-term moisture damage

  
  

If you notice a musty smell in a room, or symptoms worsen when you spend time there, mould could be the reason.

How to Assess the Mould Before You Clean

Before grabbing a bucket and sponge, take a moment to size up the situation:

How large is the mould area?

• Under 1 sqm? A DIY clean is usually safe.

  
  

• Over 1 sqm or spread across multiple rooms? It’s best to call in a professional.

  
  

Where is it located?

• On the surface of paint or wallpaper? Easier to treat.

  
  

• Behind wallpaper, plaster, or inside the wall. You’ll likely need expert help.

  
  

Does it keep coming back?

• Recurring mould often points to deeper moisture problems which must be fixed at the source.

Cleaning mould with household products, remember to always wear gloves and take proper safety precautions to protect your health

Safe and Effective DIY Mould Removal

Mould can be cleaned off walls temporarily, but you should always protect yourself from spores. Wear goggles, long rubber gloves, and a mask that covers your nose and mouth. Keep the doors to the affected room closed to stop spores spreading elsewhere but open the windows for ventilation.

Have a plastic bag handy for any mouldy clothes, toys, or soft furnishings. Soft furnishings should be shampooed, and clothes professionally dry-cleaned.

What you’ll need:

• White vinegar (undiluted)

  
  

• Baking soda

  
  

• 3% hydrogen peroxide (optional, for stubborn stains)

  
  

• Spray bottle

  
  

• Scrub brush or firm sponge

  
  

• Gloves and a face mask

  
  

• Clean clothes or a damp sponge

  
  

Step-by-step guide:

1. Prepare the area - Ensure good ventilation by opening windows or using a fan. Wear gloves and a mask.

   
   

2. Apply the treatment - Spray undiluted white vinegar directly on the mouldy spots. Leave it for 30–60 minutes so it can penetrate and kill the mould at its root.

   
   

3. Scrub with baking soda - Mix baking soda with a little water to make a paste. Use a brush to scrub the affected area gently but firmly.

   
   

4. Rinse and dry thoroughly - Wipe away residue and dry the wall completely, mould thrives in damp conditions, so drying is critical.

   
   

5. Treat persistent stains - Spray hydrogen peroxide on any remaining marks. Allow it to bubble before wiping clean.

   
   

Important: Never mix vinegar with bleach, this releases toxic fumes.

Common Mistakes to Avoid When Cleaning Mould

Even with the right tools, a few missteps can make the problem worse:

• Using bleach on porous surfaces - It can damage materials and doesn’t reach mould growing beneath the surface.

  
  

• Skipping protective gear - Inhaling mould spores can cause health issues. Always wear gloves, a mask, and goggles.

  
  

• Dry brushing - This spreads spores into the air. Stick to damp wiping or washing.

  
  

• Not drying the wall fully - Any remaining moisture can encourage mould to return quickly.

  
  

• Ignoring the cause - Cleaning without fixing leaks, condensation, or ventilation problems means the mould will likely reappear.

  
  

When to Call a Professional

While DIY methods using safe household products can help with mild surface mould, the safest and most effective way to handle mould caused by condensation and dampness is to call a professional mould remediation expert. Professionals bring specialised knowledge, tools, and techniques to thoroughly remove mould, prevent its spread, and address the underlying moisture issues that cause mould growth. This not only ensures a healthier indoor environment but also helps protect your home from further damage and recurring mould problems.

You should seek expert help if:

• The mould covers more than 1 sqm

  
  

• It keeps returning despite cleaning

  
  

• It’s behind plaster, wallpaper, or inside wall cavities

  
  

• A musty smell lingers

  
  

• People in the home have ongoing respiratory symptoms

  
  

Professionals can:

• Safely remove and replace affected materials

  
  

• Use industrial-grade cleaning and mould-prevention solutions

  
  

• Identify and fix the root moisture source

  
  

• Prevent spores from spreading

  
  

Beyond Cleaning: How to Prevent Mould from Coming Back

To keep your walls mould-free, focus on controlling moisture and improving ventilation:

• Boost airflow by opening windows or using extractor fans

  
  

• Wipe away condensation and repair leaks promptly

  
  

• Choose mould-resistant paint or plaster in areas prone to damp

  
  

• Maintain a regular cleaning routine with vinegar-based cleaners and dry surfaces well

  
  

Mould on walls signals excess moisture and can damage both your home and health. Small patches may respond to vinegar or baking soda, but recurring or widespread mould needs professional treatment. With good moisture control and cleaning habits, you can keep your walls mould-free.

Kepal Building Services provides professional mould inspections that go beyond surface checks to identifying hidden moisture problems, removing harmful mould, and helping to create a healthier home environment. Book an inspection today to ensure your walls aren’t quietly affecting your health.