The Different Types of Mould You Might Find in a Building (And What They Look Like).
Mould isn’t just unpleasant to look at, it’s a living organism that can damage property and affect health. But not all mould is the same. Different types grow in different conditions, look slightly different, and can signal different underlying issues.
Whether you’re a homeowner, landlord or managing commercial properties, it helps to understand the common types of mould you might come across, and what they’re trying to tell you.
1. Black Mould (Stachybotrys Chartarum)
Appearance: Thick, dark greenish-black, often slimy or shiny when active.
Where it grows:
Bathrooms and kitchens with poor ventilation
Around windows and sills
On walls with high condensation
Behind furniture against external walls
Risks:
This is the one most people are familiar with, and rightly concerned about. Black mould can release mycotoxins that may affect people with asthma, allergies, or weakened immune systems. It’s a strong sign of excess moisture or condensation issues.
ClearCo Tip:
Just wiping it off isn’t enough. You need to tackle the cause - usually poor airflow or hidden damp.
2. White Mould (Sclerotinia or Efflorescence)
Appearance: White, powdery or fuzzy. Can resemble salt or dust.
Where it grows:
On brick, concrete or timber
In basements, lofts or cellars
On walls or items stored in damp areas
Risks:
White mould tends to appear where moisture has seeped into materials over time. It’s not as toxic as black mould, but it’s still a sign that damp is present, and it can damage structural materials and stored belongings.
ClearCo Tip:
Sometimes mistaken for efflorescence (a harmless salt deposit). If in doubt, we can test it for you.
3. Green Mould (Aspergillus, Cladosporium, or Penicillium)
Appearance: Light or dark green, often fuzzy. Sometimes with hints of blue or grey.
Where it grows:
On food or fabrics
On walls or ceilings with leaks or poor airflow
In fridges or damp cupboards
Risks:
Different strains carry different risks. Aspergillus can be harmful if inhaled, while Penicillium can cause allergies. Either way, it shouldn’t be ignored.
ClearCo Tip:
A patch of green mould near a ceiling or corner could point to a slow leak or hidden damp behind the plasterboard.
4. Yellow or Orange Mould (Serpula lacrymans / Fuligo)
Appearance: Yellow, mustard or rusty orange. Can look slimy or crusty.
Where it grows:
On wood, plaster, or paper
In poorly ventilated rooms or hidden cavities
Sometimes found near heating systems or pipework
Risks:
Some strains are part of wet rot or dry rot fungi and can cause serious damage to timber. Others are more cosmetic but still indicate high humidity.
ClearCo Tip:
Yellow or orange mould on wood should be taken seriously. You could be dealing with more than just a surface issue.
5. Blue or Purple Mould (Some Penicillium Strains)
Appearance: Bright blue or deep purple patches, usually fuzzy or velvety.
Where it grows:
Often on food or textiles
Damp corners of rooms
On wallpaper or plaster
Risks:
Less common but still harmful to those with sensitivities. Like green mould, it thrives on organic material and points to high moisture levels.
ClearCo Tip:
Don’t assume unusual colours are harmless, unusual mould often means unusual conditions behind the walls.
What Does the Mould in Your Property Mean?
Mould isn’t just a cosmetic problem - it’s a warning sign. Whether it’s black mould from poor ventilation, white mould from rising damp, or green mould from a roof leak, every patch is trying to tell you something.
The key is to stop treating the surface and start solving the cause.
How ClearCo Can Help
At ClearCo, we don’t just clean mould, we investigate it.
✅ We identify the mould type and the conditions that caused it
✅ We use professional techniques to remove it safely and thoroughly
✅ We offer advice and preventative solutions tailored to your building
Based in Kent and covering homes, rentals, and commercial spaces, we’re the trusted choice for property professionals and families who want it sorted properly.
Concerned About Mould? Let’s Take a Look
If you’ve spotted unusual patches or smells, don’t wait until it spreads. Contact ClearCo today for a no-obligation inspection and honest advice you can rely on.