How green deposits damage the substrate?
Bricks, concrete, wood and tile may look ‘closed’ with the naked eye, but this is definetely not the case. Looking at the surface of these materials using a microscope will reveal a sponge-like structure. This structure, and how ‘open’ the structure, is called the ‘porosity’ of a material. Just like a real sponge, a porous surface is able to absorb and retain moisture. When water moves into the pores of a material, i twill evaporate at a very slow rate. An untreated surface will therefore remain moist for a long time, making it the perfect environment for algea. Water may seem harmless, but the opposite is true. Water expands significantly upon freezing (this explains why ice floats). When the pores of a surface are filled with water and the water freezes, the expansion will cause massive damage to the surface. The larger the pores of a surface, the more water it can retain and the more algea will grow. When a surface is damaged by water, or high-pressure, the algea growth will come back stronger, and faster.