Case 2
- 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:
- 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 open joints of the glass curtain wall traps and retains more dirt particles. Runoff that flows over the façade picks up all the dirt particles and redeposits them. Runoff is also channeled to flow within the open joints with larger flow volume within the vertical joints. Some overflowing of runoff may occur at the intersection points between the horizontal and vertical joints, resulting in vertical stain streaks that decreases in intensity and length away from the intersection points.
When condensation forms repeatedly on a glass surface and then dries, it is possible that the surface may be “stained.” Moisture can leach alkaline materials from glass, and evaporation then concentrates the alkaline solution; this concentrate can stain glass surfaces. Thus, if a wet-dry exposure continues for a sufficient number of cycles, stain may be detected when the glass is washed. If part of the light has been “protected”, an irregular stain may be detected when the dirt is washed away.
Materials which tend to increase moisture in contact with glass during wet-dry cycles are likely to speed staining.
Etching, frosting, or fogging caused by soap marking, or by alkaline washes from masonry cleaning processes, or by direct attack of fluorides in industrial atmospheres, or by concentrated alkalis, will result in surface damage.
Consequences
Staining and discolouration of the building façade can affect the visual quality of the building. If left unchecked, the stains may be harder and more expensive to remove. The advantages of curtain wall to provide unobstructed views to the outside might hence become unavailable to the occupants.