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First, you will need to establish why your render is discoloured. Different stains will respond better to different removal methods. While the length of time the discolouration has been left to develop will also affect the process.
Air pollution can affect the rendering of buildings in a handful of unwanted ways. Over time, the presence of pollutants begins to discolour render façades and create smoky black stains on the exterior surfaces.
Algae can form when organic matter (from rain, for instance) lingers on the façade, creating the perfect textured and damp environment for algae to grow. Seeing vibrant green, red or black algae on rendered walls is especially common in humid or damp climates.
Another common stain on render is rust, which can form when rainwater reacts with metal. This could source from overflow pipes, satellite dishes or other metal features of the property and will leave deep orange-red streaks down your building.
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Jetwashing is the go-to for rendered walls, but should it be?
Most modern render companies, including Weber Saint Gobain and K-rend, recommend using a power or jet wash to remove stains and algae growth. For more information on cleaning K rend, please click here. Power washing will clear the surface of the render of light discolouration caused by weathering, pollution and algae. A thorough power wash should restore the building to its former glory as long as the staining is not too ingrained.
However, jet and power washing aren't suitable for all types of render. While some modern renders are resilient, others, like those produced by manufacturer Sto, are more delicate and can easily be damaged or eroded by a powerful water jet. Processes like soft washing involve using detergents to lift the grime from the render before washing away, meaning much less force is needed to lift stains.
You will need to use render cleaning chemicals to get the best results from your render clean. The detergent helps lift algae and other blemishes from the exterior surfaces, leaving it looking new. In many cases, small amounts of discolouration can be removed using detergent and a sponge or brush. For mild discolouration, a 1:1 ratio of bleach and water will kill mould and algae spores.
However, more stubborn stains, and properties with more, as seen on this block of apartments for a Housing Association, will need to be cleaned using professional tools and equipment. Again, a specialist company like Spectrum can advise which detergents are most suitable for your job.
A lot of the time, discolouration and staining on rendered buildings are caused by fungus growth. Fungi quickly build on structures exposed to the elements and will often grow beneath balconies, rooflines and close to windows due to water runoff. As well as discolouring the exterior of a property, fungi can damage the render itself if not cleaned regularly.
Over time, this could cause issues and lead to the building's exterior needing to be re-rendered. Regularly applying fungicides removes existing fungi growth and helps prevent fungi from growing in the future. This is especially true when the fungicide is applied after the property has been soft-washed or jet-washed.
As well as fungi, your building's exterior will contend with algae growth. Like fungi, algae grow on surfaces exposed to the elements and form a brightly coloured pigment - typically green, red or black. You may find it especially noticeable on lighter façades, which is why cleaning white render walls from the eyesore of algae is such an urgent matter for some property owners.
Applying biocide during and after cleaning will kill existing algae and minimise regrowth, meaning your property will look cleaner for longer. Biocide should be applied to the property at least once a year to prevent algae growth.
If a patch of white render becomes severely discoloured or damaged, you can choose to re-render the surface. As manufacturer Wetherby suggests, removing the damaged older render and re-applying modern white render can be a good option.
However, as you are unlikely to achieve a finish that exactly matches the rest of the property, this should only be done when you can re-render an entire panel or by a professional team. Spectrum includes professional render colour matching services with every repair to avoid mismatched render. Our operatives will mix bespoke paint colours to blend seamlessly in with your existing property, erasing any trace of repair work.
Our patented rend-care system will help you keep your property looking its best. Our patented P.A.S.T. process combines several cleaning techniques to leave your property looking like new, with lasting results.
P - The first part of the process is planning and preparation. During this stage, we will evaluate your property, closely examine the render and draw up an access plan. We 3D print our tools to ensure they are tailored to suit the job, allowing us to clean the uncleanable. Once we have surveyed the site, we will decide which cleaning techniques and products will give us the best results.
A - The next stage involves the application of biocide. The biocide treatment will kill any algae growing on the surface of the building. Algae can discolour and damage modern render, so we must use render cleaning chemicals to remove as much algae as possible.
Our biocide treatment is incredibly effective at killing algae and removing residue. This helps us to achieve great results from our cleaning process.
S - Once we have applied the render cleaning chemicals, we use steam to remove stains, residue and discolouration. The steam is heated to 150 degrees, which makes it very effective for loosening stains. Steam cleaning is far more gentle on a rendered facade than pressure washing and removes the risk of scarring or damaging the render.
T - If any staining remains following the steam cleaning, we use a targeted treatment, applied to any stains on the render to remove residual discolouration and leave the building looking new.
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To help you learn everything there is to know about cleaning and preserving modern render, we run a monthly series of free CPD seminars. The learning objective of our CPD session is to understand better 'How to Maintain Modern Render'. The seminars take an in-depth look at traditional façade cleaning methods and their characteristics to understand their benefits and drawbacks.
Michael’s 50 years of experience in the engineering and surveying industry allows him to provide an experienced, scientific eye and consult on historic preservation.
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