Case 1
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Cause of Defects
The whitish colour stains are actually the excess of the cleaning agent that remain and react with the migrated oil from the sealant to cause some mineral salt to be formed which is white in colour.
Possible causes of failure [1-6]:
1. Inherent failure
Sealants can also fail due to incorrect specification, installation, material or design considerations.
- Inadequate provision for joint movement and thermal expansion and contraction may weaken the sealant.
- Sealants may be incompatible with the substrate.
- Poor workmanship during installation may also bring about sealant failure.
One advantage of such failures is that they become apparent during the early stages of the building life, allowing for immediate remedies to be carried out.
2. Service failure
This is a long-term failure that is caused by:
- Deterioration of sealants can be caused by prolonged exposure to water and ultraviolet light
- Progressive sealant distortion due to repeated and excessive joint movement.
- Deliberate damage. It refers to things such as vandalism
3. Material failure
This can be caused by the unstable plasticizer in the sealant might have decomposed under UV rays and has migrated into the substrate.
Consequences
Sealant defects if left unattended may result in dire consequences. The following effects may take place as a result of service failure:
- Adhesion loss. Sealants may lose their elasticity and cause gaps to be left between the sealant and the façade panels.
- Splitting or cracking. Distinction must be made between slight surface crazing and splitting/cracking even though they appear similar because crazing occurs only on the surface and may not affect the performance of the sealant.
- Dirt intrusion.
- Necking or bulging. Necking refers to the local thinning of a sealant run and bulging refers to sealant extrusion.
- Staining. Sealant has the tendency to attract or hold dirt due to its chemical make-up and its electrostatic nature. When rainwater runs over the sealants, loosely held dirt particles will be dislodged and carried downwards to form stain streaks that originates from the sealant joint. Cleaning solutions has little effect on the residues left by inorganic sealant. Chemical wash or abrasive compounds may be successful in removing the more visible stains but will not be able to completely remove the invisible surface layer of oils which initially cause the stain. Hence, the stain pattern will be seen to reoccur after a short period of time.
The breaking down of sealants could set off a series of chain reactions such as water and air penetration which further undermines the functional performance of the curtain wall.