Case 7

Cause of Defects

Many building owners give identity to their buildings by installing their company logos or names on the front façade of the building. However such minor projections from the façade could disrupt the flow of water and redistribute it, washing off dirt at some areas and depositing dirt at others, causing an unsightly effect.

The basis of staining due to protruding fixtures can be reinforced with the observations obtained from subjecting a typical tightly installed light fixture to the rain runoff simulation experiment. The resulting staining pattern can be shown from Figure 1.

Figure 1:

1. Runoff drips down vertically along the sides of the fixture. Long streaks of stains will be formed at both sides of the protrusion. (“Moustache” staining) (Flow represented by ž).
2. A few drips of runoff may flow behind the fixture and emerged below it if it attachment is not completely tight. This will cause a few long streaks to be formed at the area immediately below the protrusion. (Flow represented by ž).
3. Most of the runoff will trickle along the profile of the fixture, either dripping off its face or will continue to trickle back to the facade. (Flow represented by ž).

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:

Consequences

Staining if left unchecked results in loss of aesthetic value of the building. Long-term deposition of dirt stains on the facade may result in high cleaning costs and sometimes, the stains might become unremovable.