# Common Causes of Render Discolouration

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- URL: https://cis1976.com/common-causes-of-render-discolouration/
- Published: 2026-06-25
- Updated: 2026-06-18
- Author: Tom Alger

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If you notice green, red, and black streaks on the exterior walls of your building, it’s most likely a case of render discolouration.

A render is the exterior of a commercial or residential building. More specifically, it is the protective and decorative coating that’s applied to external building walls.

The purpose of the render is to protect the exterior from weather and moisture, while also providing a uniform or textured finish to the surface. Depending on the materials used, renders can last over 30 years.

If the exterior render loses its clean appearance, it starts to look tired over time. This is why you need to perform regular maintenance and cleaning.

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Renders are prone to discolouration because of all the following factors:

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Commercial renders experience a buildup on their surface due to pollution. This is caused by traffic fumes or urban grime. Rainwater that gets into metal fittings can also cause streaks on the render. Homes closer to the coast often experience render staining from the salt, which attracts moisture.

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Exteriors often get stained because of natural organic growth. Algae contribute to the green discolouration, while fungi and mildew cause black blotches. Red or orange staining is often attributed to rust, but it’s caused by a type of algae that appears red.

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Some render materials are more susceptible to moisture and dirt absorption. There are also instances of damaged pipes and drains that keep the render moist and accelerate organic growth. Sometimes fungal growth can secrete acid, which affects the render surface.

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The walls need to be cleaned and treated. You need to safely remove the buildup that causes discolouration and transform the exterior’s look.

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External renders can be cleaned regularly with chemicals that remove organic matter. Make sure to use chemicals that won’t damage the local environment or the render. Chemical treatment combined with pressure washing can transform the exterior surface.

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The external render doesn’t need to be cleaned only. You need to make sure that the factors that contribute to staining are fixed and cleaned. These factors include gutters or leaky pipes. This lessens that buildup on the exteriors and makes regular cleaning a straightforward task.

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Utilising a service that provides rendering cleaning ensures that trained professionals take on the task. They use specialised tools and chemicals to treat the source of the discolouration and ensure that the render is transformed, because the primary goal of render cleaning is aesthetic revitalisation.

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At CIS External Cleaning, we offer render cleaning to both residential and commercial properties, among other cleaning services. Our render cleaning process provides restorative treatment for the property’s cosmetic appeal, while commercial buildings in industrial environments require a more thorough cleaning.

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A building’s exterior render takes a beating from pollution exposure and organic buildup. This buildup creates unsightly discolouration on the walls. Regular professional cleaning and maintenance can treat discolouration and revitalise the building’s exterior.

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