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Why is there Algae on Your Render? - What Types of Algae Grow on Render?

When it first became a popular building material, render was thought to be maintenance-free. Architects and property owners believed that, once applied, render wouldn’t discolour, require cleaning or change its appearance over the years. However, now that many rendered buildings are beginning to age, we can see that this isn’t the case. Over time, algae can begin to grow on rendered facades. As it spreads, algae will discolour the surface of render and leave rendered buildings looking old, tired and in need of TLC. Understanding how and why algae grows, and how it can impact a render façade, will help property owners to properly maintain their buildings and ensure rendered facades look as good as possible.

What causes algae growth?

Algae is a natural organism that grows on more or less all external surfaces. Over recent years, it’s become a lot more common to see algae growth on both domestic and commercial premises. One of the main things that’s caused this increase in growth is the Clean Air Act. By reducing pollution, and making the air in our towns and cities cleaner, the act has caused an increase in airborne algae spores and therefore an increase in algae growth. Our slowly warming climate has also had an impact on the growth of algae on external surfaces. In addition, poor detailing on the external façades of buildings has also encouraged growth of algae. This is something that makes some properties a lot more prone to algae than others. 


The first stage of algae growth is colonisation. Algae spores are spread by the wind. In moist, humid conditions, these spores will begin to grow as soon as they land on a suitable surface. Many types of algae find rendered buildings an ideal environment. The pores in the surface of the render give the algae something to hold onto while the moisture in the atmosphere allows it to thrive.

In general, surveyors find that buildings experience most algae growth on their northern facades. This is because the north face of property gets the least sun and so is more likely to remain damp. However, properties that have poor drainage, or ongoing leaks, can experience high levels of algae growth in other areas. Once algae takes hold, it can quickly spread over the external surface of a building, especially during the wet, winter months. 

How algae can damage a rendered property

Algae growth won’t have a big impact on the core structure of a building and is unlikely to cause serious maintenance issues. However, it will have an effect on the aesthetic appearance of a property and can leave façades looking discoloured, tired and uncared for. If left untreated, algae can spread to cover large areas of a rendered façade, significantly altering the look of a property. This can make a property look older than it should and can give residents and passersby the impression that the maintenance of the building is not up scratch.

 Types of algae

 There are three types of algae that commonly grow on rendered surfaces: red algae, green algae and black algae. Green algae is the most common type and can often be removed with gentle washing. Red algae is common in Northern Ireland and Scotland and is something we’re seeing more in England as the climate becomes warmer and wetter. Black algae, though less common, is very difficult to remove and getting rid of it generally requires cleaning and the application of biocide.

Cleaning and removal 

All types of modern render, including high-quality products from manufacturers including K-Rend and Weber Saint-Gobain, require regular cleaning to remove algae and prevent regrowth. Our pioneering render care system allows property owners to restore their buildings to their original aesthetic appearance while preventing quick regrowth of algae.

Spectrum’s render cleaning process is made up of four steps. First, we prepare the area due to be cleaned. This involves assessing the current condition of the render, carrying out a thorough survey on the property and ensuring our operatives, and anyone else using the site, are kept safe throughout the clean.

The next stage involves applying a specially-selected biocide to the surface of the render. This kills any algae present on the render and helps to kickstart the cleaning process. We then use pressurised steam, heated to 150 degrees to gently remove algae and discolouration from the external façade of the building. This is a much better option than jet washing which can damage the surface of the render. If there are any stains remaining following the steam clean, we use targeted treatment to remove them from the surface. Finally, we apply a final coat of biocide to prevent the algae growing back for as long as possible

This staged process allows Spectrum to thoroughly remove the algae from the surface of a rendered building. On completion, properties that have undergone a thorough clean are restored to their original aesthetic appearance and are protected from future algae growth.

To help our operatives get to every corner of a building, and to keep access costs as low as possible, we design and 3D print our own specialist equipment. This allows our operatives to work from ropes instead of cherry pickers and scaffolding, something that can dramatically reduce costs and ensure the clean is completed as quickly as possible.

Regularly removing algae from the surface of a rendered building helps to keep the façade looking as good as possible. What’s more, regular maintenance allows property owners to monitor the condition of their properties and address any issues – like leaks, poor drainage or cracked pipes – that may be contributing to the rapid growth of algae. 

Find out more, and learn about the pioneering render cleaning services Spectrum offers, by exploring our site or getting in touch with a member of our team.

Why is there Algae on Your Render? 1Why is there Algae on Your Render? 2Why is there Algae on Your Render? 3Why is there Algae on Your Render? 4Why is there Algae on Your Render? 5
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