Case 4
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
Staining can be defined as a mark or discolouration that is not easily removed. The natural characteristics of glass make it difficult to be kept clean and susceptible to staining [1-2]:
- Glass is hydrophilic in that it attracts and holds a molecular layer of moisture on its surface and this in turn traps dust and dirt.
- Glass does not conduct electricity. As such, electric charges generated by surface friction are not readily dissipated and attracts dirt to the surface.
- The surface of glass consists of microscopic irregularities, allowing many substances to embed on the surface.
The following factors can be attributed to the degree of staining:
- The pollution content of the air where the building is resided;
- The flow pattern of rain water over building façade;
- The quality of the materials used and workmanship on the façade; and
- The façade’s design features.
Environmental factors are beyond the control of the designers. However, the degree of staining can be mitigated by controlling the pollution and understanding weather conditions.
In this case, rainwater that strikes the face of the building picks up the dirt particles and flows over the sloping roof. From this points, the runoff is allowed to flow uncontrollably and unevenly over the sloping roof onto the glass face. During light rainfalls when the runoff is slow and small in volume, it will trickle along the face and deposit dirt particles that it is unable to bring along. Stain streaks thus form in the manner shown with darker streaks along the vertical joints.
Consequences
Stains if left to accumulate and build up on the glass will affect the visual performance of the glass in providing the building occupants with good views outside and to provide daylighting into the building. Removing intense stain marks will also be more costly.