COP v3.0:maintenance; washing

16.7 Washing 

Regular washing of pre-painted roofing products increases their durability by reducing attack from airborne salts and pollutants. Unpainted products, although not recommended for use in severe or very severe environments, will also benefit from routine washing.

Washing may be carried out with a hose and a soft bristle brush, using fresh water. In areas where heavy industrial deposits dull the surface, a thorough cleaning can be ensured by using a 10% solution of household detergent and fresh water followed by a thorough rinse with clean water.

Stronger concentrations of cleaners than those recommended can damage coating surfaces, and organic solvents and abrasive cleaners should not be used. When cleaning coated surfaces, tar and similar substances may be removed with mineral turpentine, but the surfaces should then be washed thoroughly with detergent and water.

Always clean coated surfaces from top to bottom, and rinse immediately and thoroughly with fresh, clean water avoiding over-cleaning or scrubbing, which can damage painted surfaces.

The scrubbing of bare AZ coated steel cladding can remove the thin factory applied clear acrylic film and should be avoided for this reason.

High-pressure water blasting must not be used to clean pre-painted metal as it can damage the paint surface and water blasting can also force water into areas that it would not be subject to under normal weathering and thus cause water ingress.
If water runoff is used for drinking water, roof outlets must be disconnected before washing any roof or wall cladding using detergents. Care must be taken not to contaminate waterways.

16.7.1 Lichen And Mould 

Some types of local environment are particularly conducive to lichen or mould growth; including areas of wet, dark, or shaded surroundings where trees are in the proximity, overhang roof cladding or low lying valleys where moisture-laden air accumulates as fog or mist.

Lichen is a naturally occurring phenomenon with their spores being dispersed by the wind and lichen will grow even on inert materials such as G.R.P. and glass.

As lichen and mould retain moisture, their removal is in the best interest of the longevity of metal cladding, but recolonisation is very likely. Mould growth can be removed by washing down the roof or wall cladding, and applying a 2% solution of sodium hypochlorite to all surfaces by low-pressure spray, broom or brush.

The surface should be left for 5 minutes but should then be rinsed and thoroughly washed down with cold water. Household bleach contains various concentrations of sodium hypochlorite; therefore, it may be necessary to dilute it.

For example:

  • One brand has 30 g/L solution ( 3% ) — to obtain a 2% solution, 2 parts of bleach should be diluted with 1 part of water. (3 - 2 = 1).
  • Another brand has 40 grams/L solution (4%) — to obtain a 2% solution, 2 parts of bleach should be diluted with 2 parts of water. (4 - 2 = 2).
  • Another brand has 50 grams/L solution (5%) — to obtain a 2% solution, 2 parts of bleach should be diluted with 3 parts of water. (5 - 2 = 3).

If the roof is used for the collection of drinking water see 16.10 Drinking Water.


16.7.2 Graffiti 

Metal wall cladding like most vertical surfaces is subject to being defaced by graffiti. Graffiti removal is likely to affect the pre-painted finishes on metal roof and wall cladding, and before removal is attempted a small area should be cleaned as a trial. Graffiti removers may soften the paint, remove the gloss or may cause permanent damage.

Do not use MEK (methyl ethyl ketone), toluene, acetone or thinners. Overpainting or replacement are the alternative options.

There are clear removable anti-graffiti coatings available but they are an expensive option and should be compatible with the paint system.