How to Tell if Mould Is Growing Behind Drywall or Walls

black mould behind walls and drywall — Black mould that was hidden behind drywall and baseboards.

Introduction

Mould is a common household issue that thrives in damp, dark environments, making it a persistent challenge for homeowners. While some mould growth is easy to spot, like the patches that appear in showers or basements, mould hidden behind drywall often goes unnoticed until it causes significant problems.

Detecting mould early is essential for maintaining a healthy home. Prolonged exposure to mould spores can lead to respiratory issues, allergies, and other health complications. Beyond the health risks, undetected mould can weaken the structure of your home, leading to costly repairs if left untreated.

Unfortunately, identifying mould behind drywall isn’t as straightforward as spotting surface growth. It requires attention to subtle signs, the right tools, and often professional expertise. In this guide, we’ll walk you through how to tell if mould is hiding behind your walls and what to do about it.

Why Mould Grows Behind Drywall and Walls

Mould is a type of fungus that thrives in environments where moisture, warmth, and organic materials like drywall paper or wood are present. Behind drywall, these conditions can easily develop, creating a perfect hiding spot for mould to grow undisturbed.

One of the reasons mould grows so effectively in this hidden space is the lack of light and airflow. These dark, damp areas provide the ideal setting for mould spores to settle and multiply, often going unnoticed until the damage is severe.

Common Causes of Mould Behind Drywall

Water Leaks from Plumbing or Roofs: Leaking pipes, dripping faucets, or a damaged roof can introduce moisture into wall cavities. Over time, this trapped moisture creates the perfect conditions for mould to grow behind drywall.
High Indoor Humidity Levels: Homes with consistently high humidity levels—above 60%—are at greater risk of hidden mould growth. Moisture in the air can seep into walls, where it condenses and lingers, promoting mould development.
Flooding or Previous Water Damage Not Fully Remediated: If your home has experienced flooding or water damage, even small amounts of residual moisture left behind can lead to mould growth. Inadequate drying techniques or missed spots during remediation often result in hidden mould problems.
Poor Ventilation: Areas like basements, bathrooms, or kitchens are particularly prone to mould because of their high moisture output. When these spaces are poorly ventilated, excess humidity has nowhere to escape, and moisture can collect inside walls.

Understanding these causes can help you take proactive steps to prevent mould from taking hold behind drywall. However, once conditions for growth exist, mould can spread quickly, making detection and remediation critical.

Signs Mould Might Be Growing Behind Drywall

Hidden mould can be tricky to detect, but it often leaves behind subtle signs that something isn’t right. Knowing what to look for can help you identify a potential issue before it gets out of hand.

Visible Clues

Sometimes, the wall itself gives away the presence of mould:

Discoloration or Stains: Yellow, brown, or black patches on your walls can indicate mould growth. In some cases, you might notice mould spots on the face of a wall with no obvious explanation.
Bubbling or Peeling Paint or Wallpaper: Mould often develops in areas where moisture is trapped, leading to bubbling or peeling finishes as the dampness affects adhesives or paint integrity.

Odor

Persistent Musty Smell: One of the most telltale signs of mould is a lingering musty odor. If the smell is localized to a specific area, it may indicate mould growth hidden behind the drywall.

Structural Issues

Mould can compromise the integrity of drywall as it grows:

Soft, Damp, or Warped Drywall: Pressing on the wall may reveal areas that feel soft or spongy. In severe cases, drywall may appear warped, sagging, or even crumble under pressure.

Health Symptoms

Mould can affect the health of the people living in the home, even if it isn’t visible:

Increased Allergies and Respiratory Issues: Occupants may experience unexplained symptoms like sneezing, coughing, congestion, or irritation in the eyes, nose, and throat.
Other Unexplained Health Problems: Prolonged exposure to mould spores can lead to fatigue, headaches, or more severe issues like asthma flare-ups or skin irritation, especially in vulnerable individuals.

By paying attention to these signs, you can catch potential mould growth early and take steps to address the problem before it worsens.

Tools and Techniques for Detection

Detecting mould behind drywall can be challenging without the right tools and techniques. While some signs are visible or detectable through simple methods, specialized tools and professional expertise are often needed for a definitive diagnosis.

DIY Indicators

For a preliminary check, homeowners can use these simple methods:

Flashlight Inspection: Shine a flashlight along the surface of your walls to spot stains, discoloration, or surface irregularities that may indicate mould growth.
Tapping the Drywall: Gently tap the wall to check for soft spots or hollow sounds, which could indicate moisture damage and potential mould growth behind the surface.

Moisture Meters

Moisture meters are an excellent tool for identifying hidden moisture within walls, which often accompanies mould growth. These devices:

Measure the moisture levels in drywall, wood, and other materials.
Provide readings that help pinpoint areas of concern without damaging the wall.

Consistently high moisture levels behind drywall suggest conditions that may be conducive to mould growth.

Professional Inspection Services

Hiring professionals ensures a thorough and accurate assessment of potential mould issues. Experts use advanced tools and techniques to detect mould non-invasively, including:

Infrared Cameras: Thermal imaging cameras can identify temperature variations behind walls, highlighting areas with trapped moisture—a likely breeding ground for mould.
Borescopes: A small camera inserted through a tiny hole in the wall allows professionals to visually inspect hidden spaces for mould growth.
Surface and Air Testing: Professionals may collect samples from the air or surfaces to test for mould spores and determine the extent of the issue.
Specialized Expertise: Professionals can distinguish between minor concerns and serious mould problems, recommending effective solutions tailored to your specific situation.

While DIY methods can help you identify potential mould problems, professional inspection services offer more comprehensive insights, ensuring that no hidden issues are overlooked.

Risks of Ignoring Mould Behind Drywall

Ignoring mould growth behind drywall can lead to serious consequences for both your health and your home. What might start as a hidden problem can quickly escalate into a costly and hazardous situation.

Health Risks

Prolonged exposure to mould spores can significantly impact the health of those living in the home:

Respiratory Issues: Mould spores can irritate the respiratory system, leading to coughing, wheezing, and exacerbation of asthma or other lung conditions.
Allergic Reactions: People sensitive to mould may experience sneezing, runny nose, itchy eyes, and skin rashes.
Severe Health Conditions: In some cases, prolonged exposure to mould, especially toxic varieties like black mould, can contribute to chronic fatigue, headaches, or serious conditions such as Chronic Inflammatory Response Syndrome (CIRS).

Young children, elderly individuals, and those with compromised immune systems are particularly vulnerable to these health risks.

Structural Damage

Mould doesn’t just affect air quality; it can also compromise the integrity of your home’s structure:

Weakened Drywall: Mould can cause drywall to deteriorate, becoming soft, warped, or crumbling.
Damage to Wood and Insulation: Mould often spreads to nearby materials, such as wooden framing or insulation, leading to widespread damage.
Costly Repairs: The longer mould is left untreated, the more extensive and expensive the repairs become. In severe cases, entire sections of drywall, insulation, and framing may need to be replaced.

Potential Spread to Other Areas

Mould can spread quickly if the conditions are favorable:

Spore Release: Disturbing mould or ignoring the problem allows spores to become airborne, settling in other areas of the home.
Widespread Contamination: What starts as a localized issue can become a home-wide infestation, affecting multiple rooms and increasing the scope of remediation efforts.

Ignoring mould behind drywall can turn a manageable problem into a health hazard and a financial burden. Acting promptly to detect and address the issue is crucial to protecting your family and your home.

What to Do If You Suspect Mould

If you suspect mould is growing behind your drywall, it’s important to act quickly and carefully to prevent further health risks and damage. Here’s what you should do:

Steps to Take If Mould Is Suspected

Avoid Disturbing the Area
- Do not attempt to remove or clean suspected mould yourself. Disturbing mould can release spores into the air, potentially worsening the problem and increasing health risks.
- Limit access to the affected area, especially for children, elderly individuals, and anyone with respiratory conditions or allergies.
Contact a Professional for Inspection and Testing
- Reach out to a mould remediation specialist who can assess the extent of the problem.
- Professionals will use tools like infrared cameras, moisture meters, and air quality testing to confirm the presence of mould and locate hidden growth.

Overview of Professional Mould Remediation Processes

When mould is confirmed, professionals follow a systematic process to safely remove it and restore your home:

Containment
- The affected area is sealed off to prevent the spread of mould spores to other parts of the home. Negative air pressure and HEPA filters are often used during this stage.
Removal of Affected Materials
- Damaged drywall, insulation, and other materials are carefully removed and disposed of following industry standards to ensure safety.
Cleaning and Disinfection
- Surfaces are thoroughly cleaned and treated with antifungal agents to kill remaining mould and prevent future growth.
Moisture Control
- Professionals will address the underlying cause of the mould, such as leaks or high humidity, to prevent recurrence. This step may involve repairing plumbing, improving ventilation, or using dehumidifiers.
Restoration
- Once the mould has been eradicated and the area is safe, the damaged drywall and other materials are replaced, returning your home to its original condition.

By leaving mould detection and remediation to professionals, you ensure that the issue is handled safely and thoroughly. If you suspect mould in your home, acting promptly can save you time, money, and health-related stress in the long run.

Conclusion

Detecting and addressing mould behind drywall promptly is essential for maintaining a safe and healthy home. Hidden mould can pose significant health risks and cause costly damage to your property if left unchecked. Acting early not only protects your family’s well-being but also prevents the problem from escalating into a larger, more expensive issue.

If you suspect mould in your home, don’t wait. Relief Restorations specializes in professional mould detection and remediation services, offering reliable and thorough solutions for homeowners in Winnipeg and surrounding areas. Our team uses advanced tools and techniques to identify hidden mould and eliminate it safely, restoring your home to a healthy state.

Contact us today to schedule an inspection or learn more about how we can help you address mould problems with confidence and care. Your health and home deserve nothing less.

Contact Relief Restorations Today – Schedule an inspection or consultation with our team to ensure your home is protected. Let us help you safeguard your home and restore peace of mind, knowing that you’re in good hands.

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At Relief Restorations, we specialize in providing comprehensive mould remediation, water damage restoration, asbestos removal, light demolition, inspection and testing services across Winnipeg and Manitoba, Canada.

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Please note: The information on this post and website are for educational purposes only and does not replace professional inspection or remediation services or offer legal or medical advice.