http://cleanandcolourroofing.com/walls/ The exterior walls of your home are to an increasing extent, exposed to micro-organisms which are transported through the air. These growths manifest themselves in coloured deposits such as algae, mould, lichen and others. <br /><br />These micro-organisms need water to live. They themselves in turn harbour moisture which provides a fertile ground for further growths and deposits. <br /><br />The cause of these increasing growths is as follows: <br /> ■Increased environmental pollution from harmful <br /> substances from cars, industry and power stations <br /> ■Altered climatic causes, increased humidity <br /> ■Increased shade caused by trees and planting in residential <br /> estates
