Commercial jet washing guide
Can you jet wash render walls?
For K-Rend, monocouche, Weber and most modern coloured renders, high-pressure jet washing is not appropriate. It strips, etches and thins the render surface, leaves permanent visible stripe marks and fails to kill the organic growth that causes recontamination within weeks. Softwashing is the correct method, this guide explains why and how it works for each render type.
Modern rendered facades have become extremely common on new-build commercial and residential properties across London over the past two decades. K-Rend, monocouche, Weber and similar through-coloured silicone and acrylic render systems offer excellent weather resistance, a wide palette of finish colours and low maintenance requirements under normal conditions. However, these renders are not designed to withstand high-pressure water. The surface layer of coloured render is relatively thin and the pigmentation that produces the colour runs through the entire depth of the render coat rather than being applied as a separate finish. High-pressure water strips away this surface layer, removes the colour uniformly or in patches, leaves visible stripe marks and permanently changes the texture of the finished surface. Once etched or stripped, the only repair is re-rendering, which on a full facade is a significant cost.
No high pressure
high-pressure jet washing strips the surface layer of modern coloured renders and leaves permanent visible stripe marks and etching
Softwash only
biocidal softwashing at low pressure cleans all render types safely and kills organic growth spores for significantly longer-lasting results
12+ months
biocidal softwash treatment typically provides 12 months or more of protection before significant biological recolonisation
Why jet washing damages rendered surfaces permanently
When a high-pressure jet is directed at a modern coloured render such as K-Rend, monocouche or Weber, three distinct types of damage occur. First, the concentrated water pressure physically erodes the surface layer of the render, removing a fraction of a millimetre per pass but producing a measurably thinner render coat that is more vulnerable to weather, cracking and biological colonisation. Second, the jet wash nozzle leaves visible stripe marks where the pressure was highest, creating a permanent banded pattern on the render surface that becomes more visible as the surface re-contaminates. Third, and most significantly, the high-pressure washing removes the visible biological growth without killing the organisms. The algae, moss and lichen spores remain embedded in the render matrix and recommence growth rapidly, typically within weeks, recolonising the pressure-washed surface faster than an untreated surface because the washing has removed the outer protective silicone layer.
Sand and cement render, the traditional base coat system used under many paint finishes, is more robust than modern through-coloured systems and can tolerate low-to-medium pressure washing in good condition. However, even sand and cement render will show etching and stripe marking under excessive pressure, and the same problem of spore persistence applies regardless of render type. For all renders, the combination of biocidal chemistry and low pressure produces a superior and longer-lasting result than high-pressure washing alone.
By render typeCorrect cleaning approach by render type
K-Rend, monocouche and Weber coloured render
Softwash only. Apply a biodegradable biocidal render cleaning solution at low pressure using a pump sprayer or water-fed pole system. Allow 15 to 60 minutes dwell time keeping the surface wet throughout. Rinse at very low pressure or garden hose pressure only. High-pressure washing is explicitly not recommended by K-Rend, Weber and other major manufacturers. Even where K-Rend state a light jet wash is permissible in exceptional circumstances, biocidal softwashing is always the preferred approach as it kills spores and extends the period before recontamination.
Sand and cement render (under paint finish)
Sand and cement render in sound condition can tolerate low-pressure washing at 500 to 1,000 PSI with a wide fan nozzle held well back from the surface. Biocidal pre-treatment is still recommended before washing to kill the organic growth and extend the clean period. Any render with visible cracking, delamination or signs of water ingress should not be washed at pressure as this will drive water behind the render.
Painted render surfaces
The same principles as painted slabs apply to painted render. Assess the adhesion and condition of the paint coating before any washing. Well-adhered paint on sound render can tolerate low-pressure washing. Flaking, peeling or cracked paint will be stripped. Where the paint finish is sound but dirty, biocidal softwashing followed by low-pressure rinsing is the appropriate method as it avoids the risk of stripping the paint coating entirely.
Lime render (heritage and period properties)
Lime render on historic properties is extremely vulnerable to high-pressure washing. It is softer than modern renders and relies on its vapour permeability to manage moisture within the wall. High pressure drives water behind the render and erodes the lime surface. DOFF steam cleaning at low pressure is the preferred method for contaminated lime render on period buildings. Biocidal softwashing is appropriate for biological growth removal on all lime render types.
Commercial jet washing London
Professional render cleaning across London by Cloud Nine
Cloud Nine cleans all render types across London commercial and residential properties using biocidal softwashing at the correct pressure. We never use high-pressure jet washing on modern coloured renders. Our biocidal treatment kills spores at root level for results lasting 12 months or more. Contact us for a free assessment.
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Commercial jet washing help and guidance
Everything London businesses need to know about commercial jet washing.
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