White Mould
RoutineVarious, often early-stage colonies · also called fuzzy white mould
White mould is a description rather than a species, and much of it is the early stage of a colony that will turn green, grey or black within weeks. It is common on crawl-space joists, basement stored goods and the surface of overwatered plant compost. The important distinction is from efflorescence, which is a mineral deposit and dissolves in water.
Quick facts
- Appearance
- White fuzzy or cottony growth, sometimes with visible thread-like strands, on damp wood, soil, stored items and food. Many colonies darken as they mature, so white often means young rather than a distinct species.
- Moisture
- Needs surfaces that stay genuinely wet
- Smell
- Musty.
- Colours
- white, grey
- Texture
- fuzzy, stringy
- Surfaces
- wood, soil, food, concrete, fabric
How to recognise it
- Fuzzy or cottony with visible three-dimensional growth, not a flat crust.
- Does not dissolve when water is dropped on it.
- Often on wood, soil or fabric rather than masonry.
- Frequently darkens over the following weeks as it matures.
What it tells you about the building
Sustained damp. On timber in a crawl space, check whether the wood is soft — if it is, you may be looking at decay rather than surface growth.
What it gets confused with
One observation settles each of these.
Water dissolves efflorescence and does nothing to mould.
White fuzz on potting compost is a harmless saprophyte feeding on organic matter — a sign the soil stays wet too long.
Where it turns up
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.