Identifying mould · 1 min read
Black mould in commercial buildings: what it is and what to do
Stachybotrys, why colour alone tells you almost nothing, and the right sequence of steps when you find dark growth in an occupied building.
Dark growth on a wall or ceiling triggers the same question in every building: is this the toxic one? The honest answer is that colour alone tells you very little.
What black mould actually means
Stachybotrys chartarum is the species most people mean, and it produces mycotoxins associated with respiratory irritation, headaches and fatigue, with the greatest risk to children, the elderly and anyone immunocompromised. But many harmless moulds present as dark, and some genuinely problematic species do not. Laboratory analysis is the only reliable way to identify species and concentration.
What to do, in order
- Do not disturb it. Brushing, scraping or spraying releases spores into the air of an occupied building.
- Photograph and log it with a date. This matters later for insurance and WHS.
- Restrict the area if it is extensive or in a space used by vulnerable occupants.
- Get it assessed. Testing establishes species and airborne concentration.
- Treat, then verify with post-treatment readings against the baseline.
Why it is in the building at all
Stachybotrys needs sustained wetting rather than ambient humidity — a leak, a flood, a failed waterproofing detail. Its presence usually means water has been sitting somewhere for a while, so finding the source matters as much as treating the growth.