Rendered walls can be cleaned professionally — but it requires care. Here's the right approach for rendered surfaces.
Rendered walls — whether smooth render, roughcast, or textured finishes — accumulate algae and general weathering staining over time. Green algae on render is one of the most common exterior cleaning requests and one where the technique matters enormously. Too much pressure on render will cause damage, stripping the surface texture, cracking the render, or forcing water behind it where it can cause damp problems.
Soft washing is the correct approach for rendered walls. A biocidal cleaning solution is applied to the surface and allowed to dwell, killing the algae and biological growth. The solution is then rinsed away at low pressure, taking the dead material with it. For painted render, the choice of cleaning product is particularly important — some chemicals can affect paint adhesion or cause discolouration.
After cleaning, a biocidal exterior paint or render treatment can be applied to slow the return of algae. Some exterior paints now contain biocides as standard, which extend their clean appearance significantly. For properties where render algae is a persistent problem — particularly north-facing elevations in damp climates — discussing this preventive treatment with a decorator after cleaning is worthwhile.
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