Case 1
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
The pipe adjoining the wall has leaked resulting in the wall being damp most of the time. Prolonged dampness provides an ideal condition for algae to thrive.
The rough surface texture of the shanghai exposed plaster also allows dirt and other organic matter to be retained on the wall surface, providing nutrients for algae to grow.
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 |