Dutch company Respyre apply a bioreceptive layer of recycled concrete to the surface, followed by a coating of moss spores. After a few weeks the moss grows and spreads across the surface. These green walls don’t require maintenance and the moss protects the structure underneath from weathering and does not make the building damp. Our cities are getting hotter each year, and grey concrete is trapping heat and pollutants. So solutions like this could make a huge impact!