The short answer
- "Black mould" is a colour, not a species. The same organism can appear in different colours on different surfaces in the same room, and some moulds are close to transparent.
- Stachybotrys chartarum cannot be identified by eye or from a photograph. Confirming a species requires sampling and laboratory analysis, which is assessment work, not cleaning work.
- What decides how serious a patch is: where the water is coming from, how long the material has been wet, what it is growing in, and how much of it sits out of sight.
- Given the right conditions, growth can begin in around 48 hours, so drying a water event within hours rather than days is the single most useful action available to anyone.
- Killing mould is the wrong goal. Physical removal is the goal. Bleach strips colour while leaving growth inside porous materials, and it is mostly water, so it adds moisture to a moisture problem.
- No smell is not an all clear. Most significant problems produce no odour, and where there is one, the household stops registering it within days.
Black mould is the phrase people search at 11pm. It usually starts with a dark smudge behind a wardrobe or along a window reveal, then an hour of reading, and by bedtime the smudge has become a verdict. I would like to take some heat out of that without telling you it does not matter. It might matter. Just rarely for the reason the colour suggests.
Colour belongs to the surface as much as to the organism
A mould's appearance shifts with what it is eating and how wet that material is. Grown on the paper facing of plasterboard it can look like one thing, and on painted timber in the same room on the same afternoon it can look like something else entirely. Some moulds are effectively transparent and register only as a faint sheen, or a slight dulling of paint you would otherwise put down to age. Others are dramatically dark and, as far as anyone can tell by looking, unremarkable.
A dark patch does tell you something real. It tells you a material has been wet long enough for growth to establish, and that the conditions supporting it are either still present or were until recently. That is worth knowing. What it does not tell you is which organism you are looking at, and in most homes that question matters far less than people expect. For how damp behaves in this climate specifically, the wider guide to mould and damp in Brisbane homes covers the seasonal side.
Stachybotrys, and why a photo settles nothing
The species most people mean is Stachybotrys chartarum. It is real. It favours materials that stay saturated for extended periods: plasterboard, ceiling paper, cardboard, wet framing timber. And it cannot be identified visually. Not by me, not by an experienced assessor standing in the room, and certainly not by whoever replied confidently to the photo posted in a local Facebook group.
Species identification is laboratory work. Mould and moisture assessment is its own trade: an assessor maps moisture through the building fabric, chases the source rather than the stain, and where sampling is warranted, sends it away for analysis. That sits outside a cleaning visit. I do not test, sample or take moisture readings. I am studying in that field (unit NAT11429003), and studying is not practising, so assessment belongs with an assessor. Be sceptical of anyone who names a species on the spot, because that answer is not available on the spot.
What the evidence supports, and exactly where it stops
The World Health Organization's guidelines on indoor air quality and Queensland Health's public guidance point the same way: damp, mould-affected buildings are treated as a problem worth fixing, and the fix is the moisture rather than the stain. That is a sound reason to take a wet wall seriously and to act quickly.
It is guidance about buildings. It cannot be run backwards to explain what is going on inside any particular household, and I will not stretch it that way. The mould conversation online is full of people willing to draw a straight line from a mark on your wall to a person in your house. That line is not one the evidence licenses them to draw.
Scope note: I write about buildings, not people. Nothing here is health advice, and nothing here should be read as an explanation for anything happening in your household. Those questions belong with a GP or treating practitioner. My work is what the house is doing.
What actually decides how serious a patch is
None of these have anything to do with colour.
- Where the water is coming from, and whether it is still arriving. A stain that stopped growing 3 years ago is a different problem from one fed by a leaking shower.
- How long the material has been wet. Given the right conditions, growth can begin in around 48 hours. Drying a water event within hours rather than days is the single most useful thing anyone can do.
- What it is growing on. Non-porous surfaces such as tile, glass and sealed benchtops hold growth on top. Porous materials do not.
- How much there is, and how much of it you cannot see. The visible patch is often the smallest part.
- Whether relative humidity in that room sits outside roughly 40 to 65 percent for much of the year.
One thing gets missed constantly. Whether the mould is alive is not the measure of whether it is a problem. Dormant spores and dead growth still sit in the dust, still get disturbed, still need removing. Drying a wall out stops growth. It does not clear what is already there.
Removal is the goal, not killing
Most mould products are sold on the promise of killing. Wrong target. What you want is the growth physically gone from the material, and a dead colony left in place is still a colony left in place.
Bleach is the clearest example of the confusion. It strips colour beautifully, so the wall looks solved, while on porous materials the growth below the surface continues untouched. It is also mostly water, which means the last thing you did to a moisture problem was add moisture to it. On non-porous surfaces, a cloth, a detergent and genuine physical effort will remove growth properly. Vinegar comes up constantly in this conversation too, and it has real limits worth understanding before you rely on it, which I have gone through in my honest assessment of vinegar as a cleaner.
Porous materials are a different decision. Growth extends below what you can see, and the right approach depends on the material and how far it has gone. Sometimes it is cleanable. Sometimes the material has to come out. That call is not one to make from a photo either.
No smell is not the all clear
Most significant mould problems produce no odour at all. Where there is one, the household stops registering it within days, because nose blindness sets in fast and thoroughly. Visitors notice what residents cannot. So "I can't smell anything" and "I can't see anything" are both weak evidence.
The age assumption is similarly unreliable. Mould is not primarily an old-home issue. New builds have their own failure modes, including condensation forming inside steel-framed wall cavities, where nothing is visible from either side until the problem is well advanced. Old and new homes fail differently. Both fail.
The unglamorous part that actually works
Mould needs moisture, a food source and time. You cannot remove any of the 3 from a house, but you can influence all of them. Most indoor moisture is generated inside: cooking, showering, drying laundry indoors, and the plain fact of people breathing in a closed room overnight. Ventilation and extraction do more than any spray. Dehumidifiers help in the right situation, provided they are cleaned and maintained on schedule, because a neglected one becomes its own moisture and microbial problem. Which type suits a given house depends on the house, not on a rule of thumb.
Housekeeping is not the cause of mould and it will not fix a leak. It does contribute, though, and I will not pretend otherwise. Dust is a food source. Clutter blocks airflow along skirtings and behind furniture, holds humidity against cold surfaces, and hides the early signs until they are no longer early. Reducing dust, thinning out excess soft furnishings and keeping air moving genuinely shifts 2 of the 3 conditions in your favour. It just does not substitute for finding the water.
What I do, and what I do not
I clean surface mould where it is safe to do so as part of a clean, using fragrance-free products, HEPA filtration, the correct brushes and effort rather than harsh chemistry. During a Home Health Review I walk the whole house and flag where moisture and mould risk are developing: the cold external wall behind the bedhead, the bathroom with no working extraction, the laundry that dries indoors all winter.
I am not a remediator, and full remediation is specialist work with its own containment requirements. If what you have is beyond a surface clean, the honest answer is that you need someone else, and I will say so. That tends to be the most useful sentence in the whole visit.
Common questions
Is black mould more dangerous than other mould?
Colour is not a reliable indicator of anything. The same species can appear in different colours depending on the surface it is growing on, and some moulds are almost transparent. What matters is how much growth there is, what material it is growing in, how long the area has been wet, and whether the moisture source is still active. Any established mould growth indoors is worth addressing regardless of its colour.
How do I know if I have Stachybotrys chartarum?
You cannot know from looking, and neither can anyone else, including experienced assessors. Identifying a species requires sampling and laboratory analysis. Anyone confirming a species from a photograph or a glance is guessing. For most households the species matters far less than the extent of the growth and the moisture source feeding it.
Does bleach kill black mould?
Bleach removes colour, which makes a surface look clean while leaving growth intact below the surface of porous materials such as plasterboard and unsealed timber. It is also mostly water, so it adds moisture to a problem caused by moisture. Physical removal is the goal rather than killing. On non-porous surfaces, detergent, a cloth and sustained effort remove growth properly.
Is damp and mould in a house something to act on?
Yes. The World Health Organization and Queensland Health both treat damp, mould-affected buildings as something to fix, and fixing means finding and stopping the moisture, then physically removing the growth. That guidance is about buildings. It is not an explanation for anything happening to a specific person, and questions about anyone's health belong with their GP or treating practitioner.
If there is no smell, is the house fine?
No. Most significant mould problems produce no odour at all, and where there is a smell, people living in the house stop noticing it within days as nose blindness sets in. Absence of smell is not reassurance. Neither is absence of visible growth, since condensation inside wall cavities can be well advanced before anything shows on either surface.
Do you offer mould testing or inspections?
No. Testing, sampling and moisture readings are mould and moisture assessment work, and that belongs with an assessor. I am studying in that field, which is not the same as practising in it. What I do is clean surface mould where it is safe to do so as part of a clean, and during a Home Health Review flag where moisture and mould risk are developing so you know what to have properly assessed.