Case 3
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- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
The crack line harbour dirt particles which are brought down by water seeping from the crack line, thus forming the dark stains marks which are prominent over the lighter background.
Stain marks will reduce the aesthetic value of the building.
The following factors can be attributed to the extent of staining:
- The pollution content of the air where the building is resided (Table 1);
- The flow pattern of rain water over building façade;
- The quality of the materials used and workmanship on the façade; and
- The facade’s design features.
| 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: Pollutant
Staining on a facade has a lot to do with the pattern of rainwater runoff, which in turn is dependent on the facade configuration, colour, texture, as well as the “roughness” and “water absorption” properties of the materials used:
