“Black mould” is a general term commonly used to describe dark-coloured mould growing inside buildings. It is not a scientific classification, and mould cannot be reliably identified as Stachybotrys chartarum simply because it appears black.
Stachybotrys chartarum is a greenish-black mould that can grow on persistently damp, cellulose-rich materials such as plasterboard, fibreboard and paper products. However, many other mould species can also appear black, dark green or brown. Visual appearance alone is therefore not enough to identify the mould species present. US EPA
From a building and indoor environmental perspective, the more important issue is usually why mould is growing at all.
Mould growth indicates that sufficient moisture is available to support fungal growth. Addressing the moisture source is therefore fundamental to preventing it from returning.
What Causes Black Mould?
Mould requires moisture and a suitable surface on which to grow.
Common causes within homes and buildings include:
plumbing or roof leaks;
condensation;
elevated indoor humidity;
inadequate ventilation;
water ingress through walls or building envelopes;
poorly ventilated subfloor areas;
water-damaged building materials; and
materials that remained wet following flooding or another water event.
NSW Health advises that mould commonly develops in wet or moist areas with inadequate ventilation and may occur on walls, ceilings, bathroom tiles, carpets, insulation and timber. NSW Health
Bathrooms are particularly susceptible because showering creates significant moisture and humidity. However, recurring bathroom mould should not automatically be dismissed as a cleaning issue.
Persistent growth may indicate inadequate exhaust ventilation, condensation, leaking plumbing, failed waterproofing or another underlying moisture problem.
Is Black Mould More Dangerous Than Other Mould?
Not necessarily.
The term “toxic black mould” is often used online, but it can be misleading.
Some fungi, including Stachybotrys chartarum, are capable of producing mycotoxins under certain conditions. That does not mean a dark-coloured mould growing in a building is inherently “toxic”, nor can its health significance be determined from colour alone.
The US CDC advises that Stachybotrys chartarum and other moulds found in buildings should generally be treated similarly from a moisture and remediation perspective. CDC
For most building investigations, determining that abnormal mould growth and a moisture problem are present is more useful than trying to determine whether visible growth is a particular “black mould” species.
Can Mould Affect Your Health?
Yes, although the effects vary considerably between individuals.
NSW Health identifies potential effects of mould exposure including:
runny or blocked nose;
eye irritation;
skin irritation; and
wheezing.
Mould exposure may also trigger asthma symptoms in susceptible people. Most people, however, will not experience health problems simply from encountering mould spores. NSW Health
People who may be more susceptible include those with:
asthma;
allergies;
chronic respiratory disease; or
weakened immune systems.
Severe fungal infections are uncommon and are primarily a concern for people with significant immune suppression or particular underlying lung conditions. NSW Health
A mould assessment should therefore determine the building and environmental conditions, rather than attempt to diagnose whether mould has caused an individual's symptoms.
Health concerns should be discussed with an appropriately qualified medical practitioner.
Does Black Mould Need to Be Tested?
Usually, visible mould does not need laboratory testing simply to prove that mould is present.
NSW Health notes that because mould is generally visible, routine testing in homes is often unnecessary. Where mould is suspected but the source cannot be identified, an occupational hygienist or other suitably qualified professional may assist with investigation. NSW Health
Testing can nevertheless be useful where it addresses a defined question.
Examples include:
investigating suspected hidden mould;
comparing indoor and outdoor fungal ecology;
assessing areas where the extent of contamination is uncertain;
investigating unusual or complex building conditions; or
supporting post-remediation verification.
Depending on the assessment, this may involve airborne fungal sampling, surface sampling, moisture measurements, psychrometry and inspection of potentially affected building materials.
The important point is that sampling should support an investigation — it should not replace one.
The Moisture Source Is Usually More Important Than the Mould Colour
Removing visible mould without correcting the moisture problem commonly results in the mould returning.
A professional mould and moisture assessment therefore looks beyond the visible growth and considers:
where moisture is entering or accumulating;
moisture content of building materials;
indoor relative humidity;
condensation potential;
ventilation;
plumbing and building-envelope defects;
subfloor or roof-space conditions; and
the extent of affected materials.
NSW Health similarly recommends controlling moisture, repairing leaks and improving ventilation as fundamental measures for preventing recurring mould. NSW Health
This is why repeatedly cleaning the same patch of mould without understanding why it is wet rarely provides a long-term solution.
Can Small Areas of Bathroom Mould Be Cleaned?
Small areas of superficial mould on hard, cleanable surfaces can often be managed without specialist remediation, provided the moisture source is also addressed.
NSW Health recommends routine cleaning using mild detergent or diluted vinegar solution, with affected surfaces thoroughly dried afterwards. More heavily affected or absorbent materials may require professional cleaning or replacement. NSW Health
The objective is to physically remove the mould, not simply kill or bleach its colour.
The US EPA notes that routine use of chlorine bleach is not generally necessary for mould remediation and that dead mould can still cause allergic responses, meaning mould still needs to be removed from the surface. US EPA
Cleaning products should never be mixed. In particular, bleach must not be mixed with ammonia or other cleaning products because hazardous gases can be generated. CDC
What About Mould in Silicone and Grout?
Bathroom silicone, grout and other joints are frequently affected because they remain damp and can accumulate soap residue, dust and other material capable of supporting fungal growth.
Superficial mould may sometimes be cleaned successfully.
However, where mould has penetrated or extensively colonised flexible sealants, replacement of the affected silicone may be more appropriate than repeated surface cleaning.
Importantly, recurring mould around showers and wet areas can also indicate a broader moisture or ventilation issue. If growth returns quickly after cleaning, the underlying conditions should be investigated.
When Should Mould Be Professionally Assessed?
Professional assessment becomes more appropriate where:
mould is widespread;
growth repeatedly returns after cleaning;
there has been significant water damage;
the moisture source is unknown;
building materials remain damp;
mould is suspected within wall, ceiling or floor cavities;
musty odours persist without obvious visible growth;
multiple rooms are affected;
a property dispute, insurance matter or remediation project requires independent documentation; or
remediation has occurred and verification is required.
In these circumstances, the objective should be to establish the extent of the moisture and mould problem and identify what needs to change for the building to return to normal conditions.
What Does a Mould and Moisture Assessment Involve?
Depending on the building and the reason for the assessment, an investigation may include:
visual assessment of visible mould and water damage;
inspection for potential moisture sources and pathways;
moisture measurements of building materials;
temperature and relative humidity measurements;
assessment of condensation conditions;
inspection of subfloor, roof-space or other accessible cavities;
targeted surface or airborne mould sampling where justified; and
recommendations for moisture rectification and remediation.
A useful assessment should ultimately answer three questions:
Where is the moisture coming from?
How extensive is the mould or moisture impact?
What needs to be done to stop it recurring?
Preventing Mould From Returning
Long-term mould management is primarily about moisture control.
This may include improving bathroom exhaust ventilation, repairing leaks, managing condensation, improving subfloor ventilation and drying water-affected materials.
NSW Health recommends using exhaust fans during bathing and showering, improving ventilation, repairing leaks and completely drying water-damaged building materials. NSW Health
Simply painting over mould, applying an anti-mould product or replacing silicone without addressing the source of moisture may provide only a temporary improvement.
Mould and Moisture Assessments in NSW
Confluence Environmental provides mould, moisture and indoor environmental assessments for residential, commercial and other buildings across NSW.
Our assessments can incorporate visual inspection, building-material moisture assessment, psychrometry and targeted fungal sampling where appropriate, with findings interpreted in the context of the building conditions and likely moisture pathways.
Where mould continues to return, extensive water damage is present or the cause is unclear, a professional assessment can help establish the source of the problem and provide a defined pathway for remediation and building rectification.