How to remove algae on rendered walls

Weber UK

Whilst algae isn't harmful to render nor does it affect the performance of the product, it is unsightly. We look in more detail at algae growth, what you can do to prevent it and how to remove green or red algae from rendered walls.

Where does algae grow?

Algae can grow on almost any surface and the speed and severity of algae growth can often depend on the local environment. Areas more susceptible include:

  • Coastal areas
  • Woodland areas
  • Areas close to large expanses of water

North-facing elevations are also more likely to be subject to algae growth as they receive less direct sunlight, making them cooler and damper than other elevations on a building.

Algae growth isn't limited to porous surfaces, and can grow on nearly all types of surfaces including stone, glass, metal, plastic, and brickwork.

Our research into algae

Weber has worked in conjunction with Saint-Gobain Recherché Paris and with microbiologists from Université Paris-Sud to both understand the effect of the composition of render and the effect of external factors (dew point, surface condensation, temperature, and rainfall) on render.

Analysis of samples collected from the United Kingdom, Ireland, and France have identified 8 key species of algae being more prevalent in certain areas such as coastal areas and those which have similar characteristics.

How are our products helping prevent algae?

When applied, our renders are very alkaline, and therefore algae cannot grow on them. However, over time the alkalinity is reduced and algae spores can be established. 

Our renders have a high water-shedding surface and an optimised formulation with low organic content – this means there are few nutrients for algae spores to feed from. However, prolonged periods of mild and damp weather will encourage algae to grow on almost any surface, including roofs, fences and walls. 

Clean with algae biocide

Wash down render from time to time when it starts forming algae spores to prevent noticeable buildup of algae, mould and other environmental contaminants.

View our guide on render cleaning with weber CL150 →

Protect render

Whilst monocouche render is low maintenance, like any other building facade it is not immune from the gradual buildup of organic growth and dirty deposits or graffiti.

Find out how to protect render with weberend protect →

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