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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 Drinking Water.

 

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