This process involves the high pressure cleaning of a Terracotta or Concrete roof tile surface.
Terracotta Roof Tiles are usually cleaned to have visible moss and lichen removed. Terracotta tiles are made from natural clay which is naturally a moist material. Moss and lichen is naturally attracted to the roof tiles surface, and if left will continue to grow and most likely restrict the flow of rain water over the tiles surface, into the roofs gutters.
An application of an environmentally friendly anti-fungal solution should be applied to all moss and lichen prior to undertaking the roof cleaning process.
Concrete Roof Tiles are typically only cleaned when the intention after is to re-seal and re-paint/coat the roof tiles surface.
There have been various makers of Concrete/Cement roofing tiles over the Years. Some have performed very well whilst others have performed poorly, causing more issues than wanted for home owners.