How to remove algae from a facade

Green algae on a facade is one of the most common problems building owners face – especially on properties in shaded, damp spots or near greenery. Algae, moss and lichen don\’t just spoil the look of a wall; they work into the structure of the render and speed up its decay. The longer they stay, the harder they are to remove – and the greater the risk of costly repairs.This guide answers the key questions: what causes algae on a facade, why it keeps coming back after a simple wash with water, and how to remove it effectively and for good using the right products.

What is facade algae and where does it come from?

Algae on a facade are microorganisms that thrive anywhere there is moisture and even a little light. On building walls you will most often find:

• Single-celled algae – form the familiar green or yellow-green film, often most visible after rain
• Moss – develops in joints, on sills and anywhere moisture collects
• Lichen – the hardest to remove; it works deep into the structure of render and stone
• Cyanobacteria – form a dark, grey-green film often mistaken for ordinary atmospheric dirt

Algae spread fastest on north- and east-facing walls (which get less sun), near trees and shrubs, on buildings beside rivers or ponds, and on rough-textured render where water lingers on the surface.

Why does algae come back after pressure washing?

This is the most common mistake when cleaning a facade. A high-pressure washer removes the visible mass of algae and moss, and the wall looks clean straight afterwards. The problem is that algae spores are microscopic and sit deep in the structure of the render. The jet of water does not remove them – it simply spreads them across the whole surface.The result: after 2–4 weeks, once temperature and humidity are favourable, the spores germinate and the green film returns – often faster and more intensely than before.The only lasting solution is to use a biocidal product that destroys the organisms themselves, rather than just removing their visible mass.

Which facade cleaning product should you choose?

There are two main types of biocidal product for removing algae from a facade.

Sodium hypochlorite based products

Sodium hypochlorite is the most effective biocidal ingredient for removing algae, moss and lichen from render. It works fast – results are visible within about 10 minutes – by oxidising the cell structure of the organisms and destroying them to the full depth they have penetrated the render.Power Fasad is a professional product based on active sodium hypochlorite, developed specifically to remove algae, moss, lichen and mould from facades. Use it undiluted on very heavy growth, or at a 1:3 ratio for lighter films. After rinsing, always follow with the Neutral Fasad neutraliser.

Active oxygen products

A gentler alternative to sodium hypochlorite. Effective on light to moderate biological soiling and safer for sensitive surfaces. Clean Fasad, with 5% active oxygen, is a good choice when the algae film is fresh and not too heavy and the facade is to be painted afterwards.

How to remove algae from a facade step by step

1. Assess the level of soiling – a fresh green film is light soiling. A dark, deeply rooted film with visible moss and lichen is heavy soiling that needs a higher concentration or several treatments.
2. Protect the surroundings – cover sensitive plants with sheeting or water the soil around the building thoroughly. Wear protective gloves and eye protection – Power Fasad contains sodium hypochlorite.
3. Prepare the product – use Power Fasad undiluted on heavy growth, or diluted 1:3 for lighter films. Do not apply to hot surfaces or in full sun.
4. Apply the product – use a garden sprayer, or a pressure washer with a chemical-dosing (SoftWash) system at low pressure. Start at the top of the facade and work downwards, making sure the whole affected area is evenly coated.
5. Dwell time – leave Power Fasad to work for 10–30 minutes. Do not let it dry out – in hot weather, lightly re-wet the surface. For old, deeply rooted growth you can extend the time to 30 minutes.
6. Optional scrubbing – for hard, dried-on lichen, scrub the surface with a stiff-bristled brush after 15–20 minutes of dwell time.
7. Rinse with water – rinse the facade thoroughly with clean water at 80–120 bar, working from top to bottom. The dirty water should drain away from the cleaned area.
8. Neutralise – the essential step – after Power Fasad, always apply Neutral Fasad diluted 1:5 to 1:10. Spray it on, wait 5–10 minutes and rinse. Skipping this step can cause discolouration and poor paint adhesion if you paint later.

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The SoftWash method – professional algae removal without high pressure

Professional facade cleaning firms increasingly use the SoftWash method – applying biocidal products at low pressure (below 10 bar) and leaving them to dwell for a long time. It is the exact opposite of the typical pressure-washer approach.The advantages of SoftWash for removing algae:

• The product penetrates deeper into the render and destroys spores more effectively
• No risk of surface damage from high pressure
• The result lasts longer – the product works within the render, not just on the surface
• Facades can be cleaned without scaffolding – telescopic systems reach up to 20 metres

Mansser Osmo systems with demineralised water and carbon-fibre telescopic poles let you apply the SoftWash method on facades up to 20 metres high, with no scaffolding or access platform.

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