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Algae, Moss and Lichen: What Is on Your Roof, Render and Paving?
They look similar from the ground, but they are different things. Here is how to tell them apart and why it matters for cleaning.
The short answer
Algae is a thin green, black or red film. Moss is a thicker, soft, raised growth. Lichen is a flat, crusty patch that clings tightly. All three like damp, shaded surfaces, and the right treatment depends on which one you have.
Algae
Algae shows up as green, black or reddish staining or streaks, often on north-facing and shaded walls, roofs and paving. It is a thin film rather than a raised growth. On render it is the most common cause of green and black marks.
Moss
Moss grows in soft cushions or carpets, mostly in damp, shaded spots. On roofs it tends to build up where water collects, such as between tiles and along the lower edge. On paving it settles in joints and in shade.
Lichen
Lichen is flat, crusty and often pale grey, white, yellow or orange. It holds on tightly to the surface, so it is usually harder to remove than algae or moss. It is often found on older roofs, stonework and walls.
Why it matters for cleaning
The type of growth, the surface it is on and how long it has been there all affect the method. We look at what you have before we choose, and we do not guess from an unclear photo. Some marks that look like growth are actually damage, age or other staining.
Growth can come back, because the conditions that caused it, such as shade and damp, are still there. We will talk through what to expect for your property when we quote.
Questions
How can I tell algae from moss?
Algae is a flat film or stain. Moss is a raised, soft, three-dimensional growth. If you can pick it up in clumps, it is moss. If it is a stain on the surface, it is more likely algae.
Is lichen harder to remove?
Often, yes, because it attaches tightly to the surface. We look at the surface first and explain what is realistic.
Will it come back after cleaning?
It can, particularly in shaded, damp spots. How soon depends on the conditions around your property.
Can you tell me what I have from a photo?
Often we can give a good first idea. We will say so honestly where a photo is not clear enough, and look in person before quoting where needed.
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