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Should You Pressure Wash Before Getting Exterior Painted?

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  • Post published:November 26, 2019
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  • Post last modified:November 26, 2019

After a day off-roading your Range Rover is filthy. Time for a bodywork re-spray?

Ridiculous, why would you want to re-spray a car when it’s just dirty – but this is usually the default position to solving the problem of a dirty building facade.

Little consideration is given to enormous strides that have been made in building façade technologies, not only in improving building thermal efficiency but also in lowering maintenance costs – let’s take rendered building surfaces and systems as an example.

Many through colour, monocouche type, render and EWI systems (such as KREND, Wetherby and Sto), have extensive performance guarantees, as much as 25 years in some cases, so re-painting should only ever be considered as a last, not first, resort.

Most contamination to building surfaces is environmental – everyday grease, grime and bacterial staining (biofilm). In nature, biofilms are almost always a broad spectrum of species, bacteria, fungi, algae, moss, lichens, yeasts, protozoa, and other microorganisms. Painting even with the best “prior to paint” cleaning discipline will not cure the problem – only it’s visible symptoms. So expect a return of staining in a very short time.

Why not think of cleaning first, on most low-rise buildings and homes it’s no more complex than a window cleaning programme – cleaning and can be completed from kerb side – so it’s also very low cost. Conversely operator risk and health requirements dictate that, even on low-rise façades, some form of expensive access equipment is utilised to ensure painters are safe – making a painting programme very expensive.


Enormous savings can be made in replacing a planned painting maintenance cycle with a low-cost “clean and sanitize” cycle.

What to use

A good exterior cleaning contractor will want to inspect your building before recommending the right approach – most staining will be biofilm plus some general grease & grime. A cleaner which is surfactant (soapy like Fairy washing up liquid) will grab the grease and grime combined with a high purity biocide – a biocide is attracted to living organisms like a magnet is attracted to metals. It kills biofilms by cationic action in piercing cell walls.

Using a high purity biocide will guarantee that your cleaning product will not interact with any component that goes to make up your building façade. DDAC, for example, is non-oxidising its chemical composition means that it cannot affect anything that is not a living organism making it safe on sealants, coatings, thatch, etc and it will not oxidise on lead flashings, aluminium or turn uPVC yellow. So safe on all building surfaces. A big bonus in that it’s also biodegradable.

Other non-bacterial staining will demand it’s own treatment unique to what causes it, for example, iron oxides from soil splashes and other “metallic” staining caused through TV Ariel fixings  – a competent contractor will advise as to the solution.