Black Mould

What black mould is

In everyday speech, "black mould" is used for any dark fungal patch. More precisely it usually means the species Stachybotrys chartarum — a dark greenish-black film, often slimy or wet-looking.

It is not possible to identify it reliably by eye against other dark species, and in practical terms that is not necessary: the response is the same regardless of species. If there is a dark fungal film over a larger area of material, it has to be handled with care.

The species does not change what you do. How long the material was wet, and what material it is, do.

One practical difference

There is, however, one practical difference worth noting. Ordinary surface mould — the grey-green or black film on an external wall corner or on silicone — grows even where a surface is only intermittently damp, from condensation for instance. This species demands much more: the material has to be wet for a long time and it has to contain cellulose. So its presence is information in itself — it means there was water somewhere, and it was there for a long time.

How to tell it apart from similar things

A dark area on a wall is not automatically fungus, and even less often this particular species.

✓ Signs pointing to fungus

The film looks wet, slimy or velvety.
The edges are irregular and the patch grows over time.
The material beneath it reads as damp.
There is a characteristic musty smell.

✗ What else it could be

An old water stain — yellow-brown, clean-edged, dry, not growing.
Soot or dust deposits along the ceiling line or above a radiator.
Salt efflorescence — white, crystalline, no smell.
A damaged paint layer that has lifted and casts a shadow.

A measurement settles the question faster than a glance. If the moisture in the material at the patch is the same as a metre away and the patch is not changing, it is most likely an old stain rather than live fungus. If the reading at the centre of the patch is sharply higher, the question is no longer "whether" but "where the water is coming from".

Where it grows

Unlike ordinary surface mould, which can grow almost anywhere, this species needs a persistently wet, cellulose-containing material. So it is typically found:

on plasterboard after flooding or a long-running leak;
on cardboard and paper in basements;
on timber structures that have been wet for weeks;
under floor coverings after flooding;
behind finishes where a pipe leak went undetected.

If you see a film like this, it usually means moisture has been there a long time — not a few days but weeks or months.

The building type indicates where to look. In pre-war buildings it is the timber floor structure with organic infill that has suffered from a roof leak or a long-running pipe leak. In panel blocks it is the space under the floor covering after flooding from a neighbour, and plasterboard finishes in the bathroom or WC. In new builds it is a structure that stood in the rain before the roof went on and was later closed up with finishes before it had dried.

How hazardous it is

Public discussion of black mould's health effects is full of exaggeration in both directions. The facts that are useful in practice:

Fungal spores and their metabolic products can cause respiratory irritation and allergic reactions, and more pronounced complaints in more sensitive people.
The more sensitive groups are small children, older people, and people with asthma, allergies or weakened immunity.
The main practical risk is not the fungus on the wall but the spores in the air — which is exactly why how it is removed matters.

We make no claims about specific illnesses and carry out no medical assessments. If you or a family member have health complaints you associate with the state of the home, that is a conversation to have with a doctor. Our job is to remove the fungus and its cause.

Official information on the health effects of damp and mould is published by the Centre for Disease Prevention and Control.

From a practical point of view the most important conclusion is simple: of everything a person facing a dark patch might do, the worst is brushing it dry. In one minute that turns a local problem on a wall into spores settling throughout the flat, including in rooms that had no problem at all.

What to do

Never brush black mould dry
Wiping or brushing it dry lifts a large quantity of spores into the air, which spread through the whole flat and settle in other rooms. The surface must be damp before anything touches it.

Do not touch it, and contain the room

Close the door to the affected room. Do not use a fan or switch on an air conditioner that could spread spores.

Do not blow on it or brush it

Do not try to dry it out or blow it off with a fan — that spreads spores.

Book an inspection

We assess the area, the material and the moisture source.

Material removal

We cut out and dispose of affected plasterboard, cardboard or finishes.

Treatment and drying

We treat the structure and dry it back to normal readings.

What to do until the inspection:

Close the door to the affected room and limit the time spent in it.
Do not use a fan, air conditioner or air purifier with a strong airflow in that room.
Do not brush or wipe it dry, and do not try to dry the patch out.
If you know where the leak is, shut the water off and record the situation in dated photographs.
Move cardboard boxes, textiles and paper out of the room if they are not already affected.

What decides the scope of work and the price

With a dark film, the job is almost never surface treatment alone, so the price range is wider than for an ordinary patch. Four things decide the scope.

1AreaHow large the affected zone is and how wide a band around it has to be treated. Inside the material the fungus spreads further than it shows on the surface.

2Whether finishes come offPlasterboard, wallpaper and insulation with fungus in the core have to be cut out. On a dense, smooth surface, treatment is often enough.

3Whether drying is neededThere is no point treating a wet structure. Drying concrete and masonry with equipment takes days, and that is a separate cost in time and power.

4AccessWhether the affected spot is freely accessible, or under fitted furniture, behind a bath, at height or in a cramped service space.

from €40inspection

from €1.50/m²treatment

from €80minimum order

Prices

Inspection from €40. Treatment from €1.50/m², minimum from €80. In extensive cases requiring material removal and drying, we set the price after the inspection — this is usually a bigger job than surface mould.

Frequently asked questions

How do I know whether it is actually black mould?

The species cannot be identified reliably by eye. In practice that does not change what you do — any dark fungal film over a larger area has to be removed with the same precautions.

Do we have to move out during treatment?

It depends on the scale and the method. In a small case it is enough not to be in the room while the work is done. In larger cases involving material removal we recommend not using the room until the work is finished — we confirm that on site.

Can you identify the species in a laboratory?

We carry out visual inspections and moisture readings. If a particular situation calls for laboratory identification of the species, we say so openly — that is a separate service.