Greening is a natural phenomenon of algae and moss growth that has existed for as long as life has existed on our planet. Any material, including inorganic materials, exposed to the outside world, is eventually colonised by algae-like micro-organisms. Until a few decades ago, this phenomenon was hardly noticed because it took several years to manifest itself. Human action over the last few decades has significantly modified several environmental conditions in a way that is unfortunately favourable to greening:
- increased sources of atmospheric carbon feed via pollution (combustion gases and industrial gaseous/particulate emissions: soot and volatile organic compounds)
- increased sources of atmospheric nitrogenous nutrients through the intensive use of nitrogenous fertilisers, especially in rural areas.
There are also accelerating conditions: the exposure of your house to the wind, a lack of ventilation in front of the tiles, the orientation of your roof to the north or in the shade for example. To avoid this phenomenon of greening, it is important to ensure good ventilation of the underside of the tiles in order to accelerate their drying out. The rules of the profession also recommend regular maintenance of the roof in order to slow down this proliferation. It should be noted that greening, if regularly maintained, does not affect the intrinsic quality of TERREAL clay tiles.