How to Find the Source of Mould

Mould is sneaky. It can be hiding in your walls, under your floors, or quietly growing in the darkest corners of your home—and you might not even realize it until it starts to smell… or worse. Whether you’re battling persistent odours, allergies, or visible growth, this guide will walk you step-by-step through identifying where mould is coming from—and what you can do about it.

Let’s uncover the secrets behind that musty menace once and for all.

Understanding the Mould Problem

Before you can find mould, you need to understand it. Mould isn’t just an aesthetic issue—it’s a biological invader that thrives on moisture and neglect. Here’s what you need to know:

What is Mould and Why It Grows

Mould is a type of fungus that reproduces through tiny airborne spores. These spores are everywhere—yes, everywhere—but they only start to grow when they land on damp surfaces.

Common causes of mould growth include:

• High humidity (above 60%)

• Water leaks (plumbing, roofing, or flooding)

• Poor ventilation

• Condensation on windows or walls

Fungi love cellulose-rich materials like drywall, carpet, wood, and insulation. When moisture sticks around, it’s party time for mould colonies.

Health Risks and Structural Impact

Mould doesn’t just look bad—it can make you feel bad too. Some species, like Stachybotrys chartarum (a.k.a. black mould), release mycotoxins that can cause serious respiratory issues, especially for kids, seniors, or those with asthma or weakened immune systems.

Health symptoms can include:

• Chronic coughing or sneezing

• Sinus congestion

• Eye irritation

• Skin rashes

• Fatigue or headaches

Structural risks include:

• Wood rot

• Drywall deterioration

• Damaged insulation

• Compromised air quality

Left unchecked, mould can cost thousands in repairs—not to mention your health.

Why Finding the Source Matters

Cleaning visible mould is like treating a fever without addressing the infection. If you don’t find and fix the underlying moisture source, the mould will come back—and it usually brings friends.

Identifying the source helps you:

• Prevent regrowth

• Target your cleaning efforts

• Reduce health risks

• Protect your property’s integrity

Think of it like detective work. Once you know where mould’s getting its water, you’ve taken the first step in cutting off its supply and reclaiming your home.

Warning Signs You Might Have Hidden Mould

Mould doesn’t always show itself right away. In fact, the most dangerous infestations are often invisible, quietly growing behind walls or under floors. If you’re not seeing mould, you might still be living with it.

Here’s how to tell if your home might be hosting a hidden colony.

Persistent Musty or Damp Odors

You know that earthy, basement-like smell? That’s mould’s calling card. Even if you can’t see it, a persistent musty odour—especially in rooms with poor ventilation—often signals active microbial growth.

Smells strongest in:

• Closets and cabinets

• Basements and crawl spaces

• Behind drywall or wallpaper

Pro tip: Follow your nose—it’s often the first tool in your mould detection toolkit.

Health Symptoms That Flare Up at Home

If your body seems to react only when you’re at home, mould might be the culprit. Hidden mould spores can trigger a range of health issues, particularly respiratory or allergic responses.

Red flags include:

• Feeling better when away from home

• Sudden asthma flare-ups or sinus infections

• Chronic fatigue, headaches, or brain fog

These symptoms are often misdiagnosed, but when they track closely with time spent indoors, it’s time to investigate.

Staining, Discoloration, or Warped Surfaces

Water and mould go hand-in-hand, and the visual evidence can be subtle. Look for unusual staining, bubbling paint, or warping on walls, ceilings, and floors. You might also notice:

• Yellow or brown watermarks

• Peeling wallpaper or cracking drywall

• Warped baseboards or flooring

Even without visible spores, these signs often mean mould is lurking just behind the surface.

History of Leaks or Moisture Problems

If your home has had past water issues, it’s already on mould’s radar. Whether it’s a minor pipe drip or a major flood, any lingering moisture can become a breeding ground.

Risk factors include:

• Past flooding incidents

• Leaky roofs or window seals

• Overflowing gutters or poor drainage

• Unaddressed plumbing leaks

Think back: Did that “small leak” ever get properly dried out? If not, mould may have moved in.

Typical Locations Where Mould Thrives

Knowing where to look is half the battle. Mould isn’t picky—it’ll settle wherever moisture lingers. But some places are prime real estate for fungal freeloaders.

Let’s break down the hotspots.

High-Humidity Rooms: Bathrooms, Kitchens, Laundry Areas

Steam and water are everyday visitors in these spaces. Without proper ventilation, they become mould magnets.

Check areas like:

• Shower corners and tile grout

• Under sinks and behind toilets

• Around washing machines and dryers

• Window sills and exhaust fans

Tip: If mirrors stay foggy long after a hot shower, your bathroom humidity is likely too high. Invest in a good extractor fan—or mould will claim squatters’ rights.

Damp Structural Spaces: Basements, Crawl Spaces, Attics

These low-traffic zones are out of sight, out of mind—and mould loves the solitude. Combine that with poor airflow and occasional leaks, and it’s the perfect storm.

Inspect for:

• Moisture on concrete or wooden beams

• Signs of condensation or dripping pipes

• Water stains near foundation walls or rooflines

If these areas smell earthy or feel unusually damp, it’s time for a deep mould inspection.

Behind the Scenes: Walls, Under Flooring, Inside Cabinets

Mould thrives in invisible places, especially where water can hide. These areas might look perfectly fine on the outside while harbouring extensive growth inside.

Common trouble spots include:

• Behind drywall near plumbing

• Under vinyl, wood, or carpet flooring

• Inside kitchen or bathroom cabinets (especially corners)

Small leaks in these areas can silently fuel major infestations. Trust your instincts if something smells off—even without visible proof.

HVAC Systems and Ventilation Ducts

Think of your HVAC as the lungs of your home. If mould gets into these systems, it can spread spores through every room.

Check for:

• Visible mould near air vents

• Condensation inside ductwork

• Musty smells when the system turns on

Regular HVAC servicing and the use of HEPA filters can drastically reduce airborne mould risks. Yes, your air conditioner could be part of the problem!

Step-by-Step Guide to Locating the Source of Mould

Now it’s time to play detective. Finding mould isn’t just about spotting black spots on a wall—it’s about uncovering the source of moisture that keeps it alive.

Here’s a structured approach to help you trace it back to its origin.

Follow Your Nose and Check for Visible Clues

Your sense of smell is a powerful ally. A persistent musty or earthy odour often points to active mould. Begin your search where the smell is strongest.

Also look for:

• Discoloured spots on walls or ceilings

• Cracking, bubbling, or peeling paint

• Unusual condensation patterns

Sometimes, what looks like a small stain can be the tip of a much larger hidden infestation.

Use Moisture Meters and Humidity Sensors

Mould can’t survive without moisture—so find the water, and you’re closer to finding the mould.

Tools that help:

• Moisture meters: Detect damp spots behind walls or under flooring

• Humidity sensors: Monitor humidity levels (ideal range is 30–50%)

• Thermo-hygrometers: Measure both temperature and relative humidity

High readings near suspect areas? That’s your clue to dig deeper.

Inspect Plumbing, Roofing, and Exterior Drainage

Leaky pipes, cracked roofing, and clogged gutters are common culprits behind mould-prone moisture.

What to examine:

• Under-sink pipes, behind appliances

• Roof tiles, attic beams, and chimney seals

• Downspouts and slope of landscaping around your home

If water isn’t draining away from your house, it may be seeping inside—and feeding mould behind the scenes.

Carefully Investigate Hidden or Inaccessible Areas

Some of the worst mould infestations are entirely out of sight. If you suspect an issue but can’t find it in plain view, it’s time to check behind the curtain.

Check:

• Under carpets and behind baseboards

• Inside wall cavities via access panels

• Underneath sinks and bathtubs

Be cautious—disturbing mould can release spores. Always wear PPE or call a pro if you’re unsure.

Consider Using Infrared or Thermal Imaging Tools

When moisture hides deep inside walls or ceilings, technology becomes your best friend. Infrared cameras and thermal imaging tools detect temperature differences that often indicate moisture presence.

Benefits:

• Non-invasive (no tearing into walls!)

• Fast identification of problem zones

• Helps prioritize areas for professional inspection

Think of it as X-ray vision for your mould mission.

What to Do When You Find Mould

You’ve found it. That fuzzy, spotty, unwelcome guest. Now what?

Whether you’ve discovered a little patch in the bathroom or suspect a bigger issue behind the walls, your next steps are crucial. Here’s how to deal with mould safely and effectively.

Small-Scale Cleanup Tips and Safety Precautions

If the mouldy area is less than 1 square metre and it’s growing on a non-porous surface like tile or metal, you may be able to handle it yourself.

Before you begin:

• Wear gloves, goggles, and an N95 mask

• Seal off the work area with plastic sheeting

• Ensure good ventilation—open windows and use fans if possible

Cleanup method:

1. Scrub with detergent and water (avoid bleach—it’s not effective on porous materials)

2. Rinse and dry the area thoroughly

3. Dispose of cleaning materials in a sealed bag

Never mix cleaning chemicals. You want to eliminate mould, not create toxic fumes!

Preventing Future Mould Growth

You’ve cleaned it up or called in the experts—great! But how do you make sure mould doesn’t make a comeback?

Prevention is all about controlling moisture, improving airflow, and making smart material choices. Here’s your game plan.

Keep Indoor Humidity Under Control

Mould thrives in humidity above 60%. Keeping levels in check is your first line of defence.

How to do it:

• Use a dehumidifier in basements or damp areas

• Run exhaust fans when cooking or showering

• Check for condensation on windows and pipes

A simple humidity sensor can help you stay in the ideal range (30–50%). It’s an easy investment that pays off big.

Ensure Proper Ventilation Throughout the Home

Good airflow helps moisture escape and discourages mould colonies from taking root.

Focus on:

• Opening windows regularly, especially in high-humidity rooms

• Using mechanical ventilation in kitchens, bathrooms, and laundry areas

• Cleaning exhaust vents and filters regularly

Poor airflow = trapped moisture = mould’s paradise.

Address Water Intrusion Immediately

Water damage is like rolling out the red carpet for mould. Whether it’s a leak or flood, timing matters.

Your response should be:

• Act fast—dry the area within 24–48 hours

• Use fans and dehumidifiers to speed up drying

• Remove waterlogged materials like carpets or insulation if needed

The longer water sits, the more likely mould will grow.

Use Mould-Resistant Products in High-Risk Areas

Prevention can start at the renovation stage. Some materials are designed to resist mould, making them ideal for moisture-prone zones.

Smart upgrades include:

• Mould-resistant drywall (often called “green board”)

• Anti-microbial paint and sealants

• Non-porous flooring like tile or vinyl in wet areas

Think of it as installing an invisible shield against future infestations.

Expert Help: When and Why to Hire a Professional

Sometimes, mould goes beyond what cleaning sprays and elbow grease can handle. If you’re dealing with widespread growth, structural damage, or lingering health symptoms—it’s time to bring in the pros.

Here’s when to call in expert help and what they actually do.

Situations That Require a Certified Inspector or Remediator

Not all mould problems are DIY-safe. Certain scenarios demand trained eyes, specialised equipment, and strict containment procedures.

Call a professional if:

• The mould covers more than 1 square metre

• It keeps coming back after multiple cleanups

• You suspect contamination in HVAC systems or insulation

• There are health symptoms linked to indoor air quality

• There’s visible structural damage or a musty smell with no obvious source

Professionals are trained in safe removal, air containment, and pinpointing the true source—especially when it’s not visible.

What to Expect During a Professional Assessment

Hiring a mould inspector or remediation team? Here’s what typically happens:

1. Visual inspection of affected and surrounding areas

2. Moisture detection using thermal imaging or hygrometers

3. Air or surface sampling to identify mould species and concentrations

4. Root cause analysis to find out what’s feeding the growth

5. Remediation plan outlining removal, treatment, and moisture control

6. Post-remediation testing (optional) to ensure the job’s done right

We at Ex10 take a source-first approach—focusing on moisture detection and long-term prevention so mould doesn’t return.

Bonus? Most of this can be done with minimal disruption to your home.

Final Advice and Next Steps

Mould doesn’t have to be a mystery—or a menace. The key is simple: control the moisture, and you control the mould.

What to do next:

• Follow your nose and check for signs

• Use moisture meters to locate damp areas

• Call in pros for hidden or large growth

• Take steps to prevent future issues

Ex10 can help you find the source fast and fix it right. From inspection to action—we’ve got you covered.

👉Book your mould source inspection with Ex10 today.
Fast. Clear. Professional.

Frequently Asked Questions

Can You Have Mould Without Seeing It?

Absolutely. In fact, that’s one of the biggest dangers. Mould often hides behind walls, under floors, or inside HVAC systems. A musty smell, health symptoms, or history of leaks may be the only clues. That’s why tools like moisture meters, humidity sensors, and professional inspections are so valuable.

How Quickly Can Mould Develop After Water Damage?

Fast—as little as 24 to 48 hours. If water isn’t dried promptly, mould spores can settle and begin growing almost immediately, especially on porous materials like wood, drywall, or fabric. That’s why immediate drying and dehumidification after any leak or flood is critical.

Are Home Testing Kits Accurate?

Home mould test kits can give you some insight, but they’re often unreliable and don’t tell you the full story. They might detect mould spores (which are everywhere), but won’t pinpoint the source, species, or severity. For real answers, lab-based testing and professional assessments are much more dependable.

Does All Mould Need to Be Removed Immediately?

Not necessarily—but you shouldn’t ignore it, either. Some surface mould (like in grout) can be cleaned easily, while others (like hidden structural growth) require urgent professional removal. The key is identifying the type, extent, and root cause so you can take the right action—fast.

How Do I Know If I Need a Professional Mould Inspection or Just a Quote?

If you can see the mould and know where it’s coming from, a quick quote may be enough. But if you’re dealing with health symptoms, past water damage, or suspect mould in hidden areas like walls or ducts, it’s best to book a full inspection. It helps uncover the root cause and ensures nothing is missed. When in doubt, start with a consultation—many pros offer them for free.

Will a Mould Issue Affect My Home’s Value or Insurance?

Yes, untreated mould can lower your home’s value and complicate insurance claims. Buyers may back out or demand costly repairs, and most insurance policies won’t cover mould from slow leaks or neglect. Acting quickly helps protect your property and keeps you in good standing with your insurer.