Case 1

Cause of Defects

Water penetration is the infiltration of water through the pores or voids in the façades, usually jointing and cracks, arising from hydraulic pressure, air pressure, vapour pressure or a combination of these parameters. The infiltrated water could either flow inwards into the building structural frame or stain the façade. In a curtain wall, there exists three conditions for water penetration to occur. They are:

• presence of water on the surface of the curtain wall,
• an opening where water can enter and
• a driving force to move the water (Beall, 1990).

Water leakage will not happen if any one of these conditions is not present. Rain penetration can occur during less-than-extreme conditions of rain and when poor detailing, materials or workmanship creates opportunities for water to seep in.

Glass is an impermeable material that does not allow the passage of water through its surface. The generation of a large volume of runoff on glass surfaces means that its joints will have to be very tight in order to prevent rain penetration. Common causes of rain penetration are:

• sealant failure resulting in gaps in the glazing groove at the edge of the glass.
• overlap of the sealant is inadequate resulting also in gaps in the curtain walling system
• failure of seal at the frame due to movement in the system
• cracking of glass or between components
• inadequate provision for drainage in the system
• condensation on the inside of the glass resulting in excess water.

There are 5 basic types of forces (VIDEO) that can drive water through openings (Figure 1).

Consequences

Weather tightness has been identified as the most significant defect suffered by curtain walls. Its manifestation can spin off other defects in the long term:

• loss of adhesion of sealant due to chemical reaction of rain water with the constituents of the background materials
• cracking of components due to moisture movement during wetting and drying and during chemical reaction
• increase in condensation and growth of mould
• streaking and staining deterioration of joint fittings

These defects may ultimately impair the performance of the curtain wall.