Lichens and Mosses create a thin layer of organic structure which is extremely slippery even when the surface is dry. After long exposure to moss and lichen, natural stone will also be damaged, these living organisms contribute to mechanical weathering (as well as chemical weathering).
Lichens and mosses grow on essentially bare surfaces and create a more humid chemical microenvironment. The attachment of these organisms to the surface enhances a chemical breakdown of the micro layers of the rock and will nearly always create an unsafe and unstable surface.
The solution involves a very High Pressure Clean (around 4000psi) which removes the root structure embedded in the surface, unless removed completely this remaining structure forms the fertilizer for subsequent outbreaks. We then treat the surface with a Sodium hypochlorite which will sanitize and inhibit regrowth for months.
Although one High Pressure Clean should be sufficient we recommend the re-application of inhibitors particularly through the winter months or on areas that remain in constant shade or remain damp for extended periods.
Although this kind of contamination is generally a domestic problem often commercial and industrial environments will also experience the same issues with areas that have poor drainage where water pools in thin layers for extended periods.
To increase safety and reduce the risk of slip fall accidents look for these types of surfaces and check to see if Lichen or Mosses are present.