Case 2

Introduction

High Moisture Concentration Regions

Type of Building: Public Residential flats

Algae of greyish appearance on the façade. Sometimes it can be seen as stains that colour the surface. This is common on building facades to do with water runoff on the facade surface. Prolonged retention of moisture facilitate algae growth.

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“.