Case 5
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- Introduction
- Causes of Defects
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Cause of Defects
Staining at parapet wall in this case is due to the presence of railings. The stains are usually rust stains and the corrosion points occur most frequently at the weld and concrete insertion points. The railings may be painted but once the primer or paint has deteriorated, the railing will corrode.
The junction between the railing and the parapet are also areas where dirt particles can be trapped (Table 1). When rainwater flows over such areas, the particles are carried along over the parapet and deposited on the wall surface.
| Pollutants | Examples | Sizes | Sources | Possible effects |
| Aerosols | Sulphur dioxide (SO2) | Gaseous | Burning of fuels | Formation of acid rain. Reaction with water and other materials to form sulphates and chlorides to cause destruction to façade materials. |
| Soot or black smoke | Smoke from tobacco, coal, fuel oil, metallurgical industry | <1 pm | Imperfect combustion | Transported by air and deposited on facades to cause stains |
| Coarse particulate matter | Ash, dust, rock debris, mineral dust. | >1 pm | Unburnt fuel and dust from roads and industries | Transported by air for short distances and deposited more easily on horizontal or sloping surfaces to form stains. |
Table 1: Sources of pollutants