Written by Hannah Crooks, Biochemist
You might think of mould as little more than an ugly stain creeping across the bathroom ceiling or a musty smell in the basement. But these seemingly harmless patches are alive, spreading silently through homes, offices and schools. What’s more, they don’t need much to take hold — just a few airborne spores, the right surface and a little moisture.
And plasterboard, the building material lining millions of walls worldwide, offers mould almost everything it needs. Understanding why can tell us not only how to protect our homes but also how to safeguard our health.
Mould starts life as a spore. Too small to see with the naked eye, these microscopic particles are released in astonishing numbers by colonies all around us — in soil, leaf litter, compost heaps, damp timber and even in the air outside on a breezy day. A single mould colony can release millions of spores into the atmosphere in a matter of hours.
Unlike seeds, mould spores don’t carry food reserves. They are built for survival: tough, lightweight and able to travel long distances. Indoors, they arrive through windows and doors, hitch rides on clothing and pets, or infiltrate via ventilation systems. They then settle, unseen, on every available surface.
Most spores remain dormant, waiting. Without moisture and nutrients, they simply sit there, biding their time. But when conditions shift — a damp patch behind wallpaper, condensation on a cold wall, or a leaky pipe inside a cavity — spores can awaken. On plasterboard, they find both shelter and food.
Plasterboard (also known as drywall or gypsum board, depending on where you live) is one of the most widely used materials in modern construction. It is cheap, easy to install and provides a smooth finish ready for paint, tiles or wallpaper. But its very composition makes it a dream home for mould, in particular:-
Paper lining: The outer layer is cellulose-rich paper, and cellulose is the mould’s preferred fuel. It breaks down easily into sugars that mould can digest.
Porous structure: The inner gypsum core can absorb water, holding dampness for long periods.
Hidden placement: Plasterboard is usually covered by paint, tiles, or wallpaper. This concealment makes mould growth hard to detect until it has already spread widely.
Compare this with materials such as glass, metal or concrete, which don’t provide nutrients. On plasterboard, mould spores don’t just survive — they thrive.
Mould is opportunistic, but not random. For spores to germinate and develop into a colony, these 5 key conditions must align:
Moisture is the single most important ingredient. It can come from anywhere: a leaking pipe, water ingress after heavy rain, condensation on a cold wall or steam from a poorly ventilated bathroom. Even a minor spill that seeps into plasterboard and isn’t dried quickly can become the starting point for growth.
A one-off splash that dries in hours may not cause much harm. But prolonged dampness is different. When plasterboard remains wet for days or weeks, it becomes a continuous source of food and water supply for mould spores. Persistent dampness is why basements, crawl spaces and poorly ventilated bathrooms are the most common hotspots.
Moisture doesn’t have to be liquid. When relative humidity indoors climbs above 60 per cent, surfaces can become damp enough to sustain mould. Bathrooms after hot showers, kitchens during cooking, or any space with poor airflow can maintain this level for hours every day. Over time, that’s enough to allow spores to germinate.
Mould is adaptable, but most species thrive in the same temperature range we enjoy — between 20°C and 30°C. This overlap makes our homes perfect incubators. Some species even tolerate extremes, with growth documented at close to freezing and up to 50°C. But in general, our climate-controlled interiors are mould’s comfort zone.
Finally, mould needs something to eat. On plasterboard, the cellulose paper lining provides a ready-made buffet. Add a sprinkling of house dust, dirt and skin cells, and spores have more than enough fuel to build colonies.
When these steps are able to flow in succession, mould can multiply & spread, fast.
Deposition – Spores land and rest on the surface.
Activation – Once moisture is available, they absorb water and begin to swell.
Germination – Hyphae, fine thread-like filaments, sprout from the spore and dig into the plasterboard.
Colonisation – These filaments spread and branch, forming a dense network called mycelium.
Sporulation – Once the colony matures, it produces new spores that rise into the air, starting the cycle again.
Under the right conditions, visible mould can appear in as little as 24 to 48 hours after water exposure. Within a week, a small patch can become a sprawling growth, ready to contaminate new areas.
At first, mould might seem like a cosmetic issue. A patch of black or green on a wall, while unsightly, doesn’t look threatening. But research shows that mould’s impact on human health can be serious.
The health risks are amplified because mould continually sheds spores. Once established on plasterboard, colonies act as factories, pumping millions of microscopic particles into the air we breathe.
Mould doesn’t just live on plasterboard — it eats it. By digesting cellulose, mould gradually weakens the paper lining and infiltrates deeper into the gypsum. Over time, plasterboard becomes soft, crumbly and structurally compromised.
The result? Walls that sag, ceilings that collapse and repairs that require full-scale replacement rather than simple cleaning. In some cases, extensive mould growth can even render homes temporarily uninhabitable.
The story of mould isn’t just about individual homes — it’s increasingly about global change. Rising temperatures and more frequent heavy rainfall linked to climate change are expected to make mould problems worse worldwide.
All of this means more opportunities for spores to germinate and spread. As our climate shifts, mould is likely to become not just a nuisance but a growing public health challenge.
Why mould matters more than you think
It’s easy to dismiss mould as a minor inconvenience, something to scrub away with bleach. But its biology tells a different story. Mould is opportunistic, persistent and everywhere — a living organism that only needs the right break to thrive.
And once it has settled into plasterboard, it’s not just your walls at risk. It’s your air quality, your health and, ultimately, your home itself.
Mould spores drift constantly around us, invisible and patient. Plasterboard, with its cellulose paper lining, offers them an irresistible opportunity. Add moisture, humidity and warmth, and those spores awaken — feeding, spreading and releasing new generations into the air we breathe.
Stopping mould requires vigilance, but it isn’t impossible. By controlling moisture, managing humidity and checking vulnerable areas, we can prevent the silent spread inside our walls.
Because once mould makes itself at home, it doesn’t just stay put. It grows. It spreads. And it shares our air.
National Institutes of Health (NIH) – Indoor Mould and Health Effects
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Centres for Disease Control and Prevention (CDC) – Mould Basics
Environmental Protection Agency (EPA) – A Brief Guide to Mold, Moisture, and Your Home
World Health Organization (WHO) – WHO Guidelines for Indoor Air Quality: Dampness and Mould
British Gypsum – Moisture and Mould in Buildings
National Institutes of Health (NIH) – Indoor Mould and Health Effects