Case 2
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
Singapore’s tropical climate offers an abundance of sunlight and rainfall for algae to grow.
Dust that is blown off the ground and is retained on the facade are sources for nutrients.
On external wall surfaces shaded from the direct rays of the sun and where humidity level is high, fungi rather than algae will proliferate. Fungi are unable to synthesize their own organic food and thus have to rely on their medium on which they are growing to provide the nutrients necessary for their growth. Bare plastered walls such as Shanghai plaster are favourable for fungi growth.
The water collected on ledges allows the moisture levels to remain high and encourages the growth of fungus.
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.
| Algae species | Examples | Conditions for growth | Staining effects |
 Blue-green algae(Source: Los Alamos National Laboratory) | Schizothrix, Anacystics, Chlorococcum, Calothrix, Scytonoma, Oscillatoria | Higher levels of moisture from runoff flow on facades. Thrives best when surface remains damp most of the time. | Light green patches. Can proliferate on new building facades. |
 Green algae Brown algae
 Red algae | Green, red or brown powders or filaments which may or may not be slimy depending on the moisture condition | May occur on all types of building surfaces |