What causes mould on interior walls?

If you’ve ever cleaned mould off your walls only for it to return a few weeks later, you’re not alone. It’s a problem plenty of us face, especially during the colder months.

The good news? There are ways to break that cycle, because tackling mould isn’t just about cleaning away what you can see, it’s about understanding what’s helping it grow in the first place.

In this guide, we will cover:

• What causes mould on interior walls
• Impacts mould can have on your home
• Why some homes are prone to mould
• How to stop mould returning

What causes mould on interior walls?

Mould needs three things to develop in our homes:

1. Moisture
2. Somewhere to grow
3. Time

But without moisture, the other two aren’t much use to mould. The trouble is, condensation has a habit of making itself at home.

Everyday things like cooking, showering and drying clothes can add moisture to the air. When warm, moisture-filled air meets cold walls and ceilings, tiny droplets of water can form.

If that moisture sticks around, it can create the perfect conditions for mould to grow.

That’s why you’ll often find mould in bathrooms, bedrooms, kitchens and around windows.

Of course, condensation isn’t the only way moisture finds its way into our homes. Leaking pipes, damaged roofs, rainwater getting through external walls and moisture rising from the ground can all cause damp patches where mould may develop.

That’s why it’s worth understanding where the moisture is coming from before deciding how to deal with it.

A condensation problem needs a different approach to a leaking pipe or water getting in from outside.

The hidden impacts of mould in your home

Mould isn’t just something you’d rather not see on your walls.

It can leave rooms smelling damp, stain walls and ceilings, damage paint and make a freshly decorated room look tired much sooner than you’d expect.

It’s not just about what it does to our home either, because mould can affect your health too.

Exposure has been linked to respiratory problems and can make allergies and conditions such as asthma worse, particularly in children and older adults.

It’s something none of us want around our homes, especially in our children’s rooms, which is why even if it is just a small patch in a corner, it’s worth taking seriously.

Why some homes are more prone to mould

Some homes seem to struggle with condensation more than others and there are a few reasons why.

Homes with poor insulation can have colder walls where condensation is more likely to form. Having said that, well insulated, more airtight homes can experience condensation too if there isn’t enough ventilation to let moisture escape.²

It might sound counterintuitive, but keeping condensation under control is really a balancing act. Your home needs to hold onto enough warmth to keep walls from getting too cold, while still having enough ventilation for moisture to escape.

Some rooms are simply more prone to mould than others too. Bathrooms can quickly fill with steam, kitchens create plenty of moisture and even bedrooms add moisture to the air while we sleep.

Furniture can be a likely source of problems too. Large wardrobes or sofas pushed up against a wall can reduce airflow and create areas where moisture gets trapped, giving mould the chance to grow.

A good clue that condensation might be the problem? A large amount of water droplets on windows in the morning or mould appearing behind furniture where air doesn’t circulate as easily.  You might also notice it getting worse every winter.

How to stop mould returning

The best way to tackle recurring mould is to deal with the conditions helping it grow.

Simple habits can be helpful for any home, like:

• Using extractor fans when cooking or showering to help remove excess moisture
• Opening windows regularly to improve ventilation and let moisture escape
• Keeping your home heated during the colder months to help prevent walls from getting too cold

Of course, these habits can make a real difference, but some homes still struggle with condensation no matter how much you try to keep on top of it.

That’s often when people start looking for a little extra help from the paint they apply to the walls. Stain-blocking paints can cover up the marks mould leaves behind, while traditional anti-mould paints use additives to help stop it growing.

The trouble is, neither necessarily tackles the moisture that’s helping mould grow in the first place and if that moisture stays, mould always has what it needs to make a return.

We thought, why wait for mould to become a problem when paint could help tackle the condensation behind it? That’s the thinking behind Heroes Shield.

Inside every tin of Heroes Shield is some rather clever Micro-Sphere Technology (sounds technical, we know). It absorbs and holds onto the warmth already in your home to keep the surface of the wall warmer, giving condensation less chance to form and mould a lot less to work with.

Then, you just paint over it with any interior paint you like. Your walls still look exactly how you want them to, there’s just a little more going on behind the scenes.

Every home is different and sometimes it’s easier just to talk through what’s happening in yours with someone, isn’t it?

We’ve got a friendly technical team here at Heroes who know a thing or two about mould, condensation and paint, and they’re always happy to chat through your particular situation and help you work out the best way forward. Give us a call on 01254 936151 or drop us an email at [email protected] and we’ll be happy to help.

Frequently asked questions

Can mould grow on freshly painted walls?

Unfortunately, yes. A fresh coat of standard paint doesn’t remove the conditions mould needs to grow. If the underlying conditions are still there, mould can make an appearance on freshly decorated walls just as easily as it can on older ones.

Can mould spread from one wall to another?

Mould releases tiny spores into the air, which can settle on other damp surfaces around your home. If the conditions are right, new mould can begin to grow in other rooms or on nearby walls.

Which rooms are most likely to develop mould?

Bathrooms, kitchens and bedrooms are the most common areas because they produce high levels of moisture through showering, cooking and even breathing while sleeping. Utility rooms where clothes are dried indoors are also particularly prone to mould.

Sources

1. Ministry of Housing, Communities & Local Government, English Housing Survey 2024 to 2025: perceptions and impacts of housing quality, 2026
2. Department of Health and Social Care & Ministry of Housing, Communities and Local Government, Understanding and addressing the health risks of damp and mould in the home,  2026