Case 1

Cause of Defects

The formation of algae growth on the tiled surfaces is mainly attributed to the presence of a film of moisture and the biological agents in air.

The film of moisture on the tiled surfaces after rain has allowed the algae spores to adhere to the tiles. Under sunlight, the algae growth spread over large areas.

Possible sources of water:

1. The primary source of moisture is rain water which penetrates or comes in contact with the tiles. The rainwater is unable to dry quickly and thus allows water to form a film on the surface [1].
2. Rising dampness

From the picture, the algae growth occurs not far from the ground DPC level. Another possible contributing factor of moisture is ground water drawn up a wall [2].

Algae Growth

Algae growth has been characterised by two (a) factors attributed to the environment (b) factors attributed to the building envelope. Environmental factors consist of climate, thermal amplitude, precipitation, hygrometry (humidity), distance from the sea and presence/absence of vegetation. Precipitation and hygrometry directly affect the availability of water on to building facades, which is widely known as one of the key requirements for algae growth. In Singapore, the high humidity and precipitation result in buildings experiencing high amounts of water contact throughout the year. The closeness of the building to the sea can also result in higher atmospheric humidity, leading to a greater chance of algae growth. Building related factors affecting algae growth are high alkalinity (e.g. fresh concrete, high in alkaline helps algae to grow), excess surface moisture, windborne transport (orientation), and rain streaks that carry the algae spores down a façade.

Left unchecked, algae will grow on surfaces to create an aesthetically subjective discolouration with various shades of green, orange, black or blue. Besides being aesthetically unpleasant, biological growth on facades may also cause deterioration and further weathering to the wall.