Black mould in a crawl space
The colour people worry about most and the one that identifies least. Dozens of unrelated species are black, and so is ordinary mildew on grout.
1 likely answer.
The species matters less than you think
- Public health guidance is to remove all indoor mould regardless of type. The CDC and EPA do not recommend routine species testing for ordinary households, because the response does not change: find the water, stop it, remove the growth.
- “Toxic black mould” is a marketing phrase, not a category. Stachybotrys is real and does need soaked material to grow, so finding it tells you something useful about your building. But the health effects that are well established — allergy, asthma aggravation, irritation — are not specific to it.
- Mould without water does not persist. Cleaning growth while leaving the moisture source is why it comes back. The leak, the condensation or the ventilation is the actual problem.
Call a professional for areas larger than about 10 square feet, for anything in HVAC ductwork, after sewage or flood water, or if anyone in the household is immunocompromised or has a lung condition.
The likely answer
1.Stachybotrys (Toxic Black Mold)
InvestigateVery dark greenish-black, and characteristically wet-looking or slimy rather than dusty. It grows in flat sheets or patches on paper-faced drywall, and dries to a sooty powder only when the water source is removed.
How to know it is this one
Wet, slimy appearance rather than the dusty or fuzzy look of common moulds.
What it means: Sustained saturation. The important task is finding and stopping the water, not naming the fungus — because anything you clean will return within weeks if the source is still there.
More on stachybotrys (toxic black mold) →Still not sure?
The key adds texture and surface, which separate these far better than colour does.
Identify it step by step