Case 2

Introduction

Biological Staining

Type of Building: Industrial

Though metal surfaces are impermeable, the presence of abundant moisture, sunlight, plant spores and nutrients from soil are adequate for biological growth even on metal surface.

Atmospheric dust can be collected at horizontal surfaces such as grooves. In this case, stains are formed on the facades of residential buildings due to rain washing down the dirt that are accumulated at the jointing grooves of expansion joints of the buildings (Figure 1).

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.

See also Staining of Facades