How to Remove Algae and Black Spots from Patios

March 2026 • 5 min read

Green algae and black spots (often lichen or mould) are common on UK patios, especially in shady, damp gardens in Somerset, Frome and Bath. They make surfaces slippery and dull. Here’s what causes them and how to remove them properly.

Why patios go green and black

Algae thrives in damp, shaded areas with little sun. Overhanging plants, walls and north-facing slabs encourage it. Black spots are usually lichen or dark mould – they cling to the surface and need the right treatment to shift. Both are more common after mild, wet winters and in areas with poor drainage.

What works: professional pressure washing and treatment

For a lasting result we:

• Apply a suitable treatment to kill algae and lichen at the root.
• Use controlled pressure washing so we clean the surface without damaging slabs or joints.
• Rinse thoroughly so no residue is left.

DIY jet washers often only blast the top layer; the growth returns quickly. We use methods that give a deeper clean and longer-lasting results for patios in Frome, Bath, Trowbridge and surrounding areas.

Preventing regrowth

Improve drainage where you can, trim overhanging foliage to let in light and air, and sweep leaves and debris regularly. An annual or biennial professional clean keeps growth under control. See our best time to clean patios and decking for when to book.

Customer FAQs

Are black spots on my patio dangerous?

They’re not harmful to health but make the surface slippery and can damage the look of the paving. Professional cleaning removes them safely.

Will pressure washing damage my patio?

Not when done correctly. We set pressure and technique to your slab type (e.g. Indian sandstone, concrete, block) to avoid damage. See pressure washing mistakes to avoid.

Do you clean decking with algae too?

Yes. We offer decking cleaning and patio cleaning across Somerset and Wiltshire.

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