Case 3

Introduction

Algae Growth Close To The Ground – rising dampness

Type of Building: Public building

Algae was observed on the external facade near the ground level. This may indicate the presence of ground water rising from the ground. With a film of moisture adhered onto the facade, the dirt and other particles that promote algae growth would be attracted to the film.

Algae are classed as aeroterrestrial as they spread through windborne spores and colonise in a biofilm on a surface, and when the conditions are susceptible, they will grow organically. They are photosynthetic and must have sunlight to continue growing. Although mostly green due to the presence of chlorophyll, black, blue, red, orange and yellow algae (depending on the number of other pigments within it) are found on all types of façade materials, including rendering, glass, aluminium and granite.

Algae thrive best where there is sun, moisture and nutrients. Dirt that is blown off the road and retained on façades becomes a source of nutrients. As such, algae are commonly found mainly outdoors on external façades. Common species of algae that may be found on façades are Trentepohlia odorata, Chlorococcum and algae comprising Scytonema, Schizothrix and Anacystics.

For more information on staining issues on facade, please visit “Staining of Facades“.