Algae build-up can be a problem on hard landscaping, creating a slippery residue and a hazard underfoot.  Algae tends to flourish in damp, shady and humid areas and, in the UK, build-up is especially common in the autumn and winter.

Different types of algae

Algae comes in different forms and often causes a green film or powdery deposit on pavers.  The term algae also includes moss; Liverwort – the flat green growth with tiny leaf-like lobes, and crust-like Lichen. Jelly-like growths are also common; they are often black or dark green and are caused by a cyanobacteria called Nostoc.  None of these growths are hazardous – infact, lichen is particularly common in areas with clean air, so its appearance can be a positive sign – but slippery hard surfaces can be.

Another common problem is black spot – a speckle-like deposit that can be black or white.  Black spot is a dust-like lichen that originates from plants and trees. It colonises on pavers, sending tendrils or ‘hyphae’ down into any cracks or porosity, searching for nutrients. It takes about 2-3 years to become established below the surface and it creates a slippery residue on the surface of pavers. 

Addressing problem areas

Why water doesn’t work

A pressure washer and often a dose of household cleaner is a common go-to solution for slippery pavers.  However, excessive water only makes conditions even better for algae to flourish and pressure washing can damage the surface of the pavers, any sealer applied and it will loosen grout.  Water also won’t target hyphae or filaments anchored into place below the surface.   A specialist approach is necessary to effectively remove residue and microspores below the surface; any treatment used needs to break-down the slippery residue; to have a bleaching action to restore the colour of the paver, and to target any growth below the surface. 

Care should be taken in selecting a suitable treatment.  If a solution is acidic, it will damage acid sensitive material and erode the grout joint.  We recommend ECOPROTEC Black Spot & Algae Remover which can be safely used on all types of natural stone, concrete, brick and porcelain.  This treatment removes all types of organic residue, slippery matter and stains, breaking down hyphae below the surface, as well as preventing regrowth.  When applying the Remover, it’s also important to treat the whole area of paving, for a uniform appearance.   

Pavers before & after treatment with ECOPROTEC Black Spot & Algae Remover

Removing large deposits and applying ECOPROTEC Black Spot & Algae Remover

Before washing pavers, any large, mossy deposits should be removed.  A long-handled block paving brush is a useful tool.  The whole area should then be swept clean to remove other residue, dirt and leaves.  

ECOPROTEC Black Spot & Algae Remover should be applied neat to swept pavers, using a watering can or light pressure garden spray, where it fizzes during treatment.  It should be left to act for 2-4 hours and surfaces then hosed with clean water.  The solution can be used on dry and slightly damp surfaces and should be applied during a morning or afternoon of fair weather.  See a video aid on the product page.

After treatment, it’s worth protecting the surface.  The ECOPROTEC range includes four water-based solutions for external paving: ECOPROTEC Ultimate SealerPatio Sealer and Colour Enhancing Sealer for natural stone and barrier treatment, Pre Grout Protection, for matt porcelain pavers.  All of the treatments help prevent the absorption of moisture and organic particles, reducing staining and the spread of algae.

For more advice and information about other ECOPROTEC cleaning and sealing solutions, please visit or contact the ECOPROTEC technical team on 01823 666213 and email  

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