Black Streaks and Rapid Darkening of Facade

Black streaks and rapid darkening of facade: A (left elev.), B (middle) and C (right elev.)

Staining is defined as a mark or discolouration that is not easily removed. It is identified as one of the major concerns of defect. Staining is caused by other situational factors such as the orientation and height of building³⁰. In this case, the adjacent building blocks off the sunlight and regular rainwater flow, hence self-cleaning effect decreases which resulted in dirt staining. Presence of V shaped columns behaves like ledges that increase in retaining and accumulation of dirt particles. The concentration of runoff at some areas on the V-shaped column may result in irregular washing effect³¹. As photocatalytic activity is dependent on consistent amount of water. Irregular washing effect, together with accumulation of dirt particles may result in irregular photocatalytic activity on the V-shaped column, resulting in long black streaks visibly seen on the three elevations of the facades.