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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 start 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 grow and how it can impact a render façade will help property owners properly maintain their buildings and ensure that 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 domestic and commercial premises. One of the main things that have 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 a rise 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. Also, poor detailing on the exterior façades of buildings has encouraged the 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. The wind spreads algae spores. 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 render's surface 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 the property gets the least sun and is more likely to remain damp. However, properties that have poor drainage or ongoing leaks can experience high algae growth levels in other areas. Once algae take hold, it can quickly spread over the external surface, especially during the wet, winter months. 


How algae can damage a rendered property


Algae growth won’t significantly impact the core structure of a building and is unlikely to cause serious maintenance issues. However, it will affect the aesthetic appearance of a property and leave façades looking discoloured, tired, and uncared for. If left untreated, algae can spread to cover large areas of a rendered façade, significantly altering a property's look. This can make a property look older than it should and give residents and passersby the impression that the building's maintenance is not up to 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 are the most common type and can often be removed with gentle washing.

Red algae are common in Northern Ireland and Scotland and are something we see more in England as the climate becomes warmer and wetter. Black algae are less common but are tougher to remove. It generally requires cleaning and the application of biocide.


Cleaning and removal 


All modern render types, 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 algae's quick regrowth.


Spectrum’s render cleaning process is made up of four steps. First, we prepare the area due to be cleaned. This involves assessing the render's current condition, 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 building's external façade.

This is a much better option than jet washing which can damage the surface of the render. If any stains remain following the steam clean, we use targeted treatment to remove them from the surface. Finally, we apply a final biocide coat to prevent the algae from 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 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, which 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 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. 


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

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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