Lichen And Mould

Lichen is a naturally occurring phenomenon with its spores being dispersed by the wind. Lichen will grow even on inert materials such as G.R.P., glass, and painted or unpainted metal roofs.

Time of wetness of a surface affects lichen and mould growth. Sheltered and shady environments are particularly conducive to its growth and although light-coloured roofs may stay wet for longer than dark roofs, it can equally proliferate in open areas on dark coloured roofs.

Lichen and mould retain moisture, are acidic, and have tiny roots that can penetrate a paint coating. Removal is necessary to prevent damage to the organic coating, but recolonisation is very likely. Where lichen has been treated, regular inspection should be undertaken to curtail spread of re-growth.

Lichen Damaged Roof Cladding

Lichen-damaged Roof

 

Lichen 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).