Oxidised roof paint and how we clean it

Oxidised Painted Roofs

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As painted metal roofs age, exposure to UV, heat and weather can cause the surface of the coating to gradually deteriorate. This is known as oxidation or chalking and usually presents as a faded, dull or powdery surface.

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It's important to understand that oxidation isn't dirt sitting on top of the paint, it is deterioration of the paint coating itself.

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There are two ways we can approach cleaning an oxidised roof:

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1. Soft washing – our preferred method

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In most circumstances, we opt to soft wash an oxidised roof. This removes mould, organic growth, dirt and other contaminants while minimising unnecessary removal of the remaining paint coating.

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The oxidised or chalky appearance may remain after cleaning because removing it would mean physically removing some of the deteriorated paint itself.

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Leaving this oxidised layer in place is not generally considered harmful to the sound coating underneath. The oxidation is primarily a symptom of the coating ageing and weathering rather than a contaminant that is actively attacking the remaining paint.

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For this reason, where preservation of the existing coating is the priority, we generally believe the less abrasive approach is the most appropriate.

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One consequence is that physical contact with heavily oxidised paint can sometimes remove some of the chalky material. Footprints, hoses, hands or other contact during cleaning may therefore leave areas that temporarily or permanently appear cleaner or different from the surrounding surface.

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2. Physically removing the oxidation

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It is possible to use a more aggressive pressure cleaning process to remove much of the loose, oxidised surface material.

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This can leave the roof looking cleaner, brighter and less chalky, but it's important to understand what is happening here. We're not simply removing dirt, we are removing part of the deteriorated paint coating.

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This process also creates considerably more paint coloured wastewater and residue, potentially requiring additional management of gutters, downpipes, drainage areas, walls, concrete and surrounding vegetation.

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We therefore consider oxidation removal primarily an appearance-focused treatment, rather than something that is inherently better for the longevity of the existing coating. The reality of the situation is that at this stage, you're choosing between two different management options for a coating that is already irreversibly compromised.

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Our general approach

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Unless there is a specific reason to do otherwise, The Pressure Washing Company will generally soft wash oxidised painted roofs.

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Our priority is to remove contaminants while preserving as much of the remaining coating as reasonably possible.

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If a customer would prefer the chalky oxidised layer to be physically removed for aesthetic reasons, this can be discussed before work begins and, where appropriate, incorporated into the scope of works. Please let us know prior to quotation if this is your preferred method/outcome.

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Neither method repairs deteriorated paint. Where oxidation or coating breakdown has become significant, repainting or recoating is ultimately the appropriate method of restoring the roof's protective and aesthetic finish.

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Tip:

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Repainted roofs gather mould at a faster rate than a factory baked paint finish. Keeping your roof surfaces cleaned and maintained will help to extend the life of your property. 

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Whilst living in Townsville's climate will always present challenges for property maintenance, mould and other biological growth can worsen the problem by:

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• Holding moisture against the coating for longer after rain or dew.

• Trapping dirt, salts and other contaminants against the surface.

• Creating a biofilm that can keep the surface wetter and interfere with normal drying.

• In coastal environments, trapped chloride salts are particularly undesirable because once the coating is sufficiently compromised, they can contribute to corrosion of the underlying metal.