Case 2

Cause of Defects

Curtain walls are generally based on the fixing of vertical mullions to which transoms, frames and insulated panels are attached.

Resistance to leakage depends on the sealant, internal drainage and weep system, and detailing which is always subjected to movement, and thus deteriorates over time.

Joints fail due to reasons such:

1. sealant failure resulting in gaps in the glazing groove at the edge of the glass.
2. substrates are not free from contaminants, which eventually lead to poor adhesion.
3. In-plane stress created by column shortening. The curtain wall is designed as as a non-structural element only to resist lateral wind loads perpendicular to the plane, any in-plane load or stress created by column shortening or seismic activities can cause the curtain wall joints and sealant to fail and thus create new paths for water leakage or enlarging the existing path. To overcome this problem, provision must be kept before selecting the height of curtain walls and fixing it.

Window sills and horizontal or near horizontal surfaces tend to have greater tendency of accumulating runoff. This accumulated water caused penetration through the joints where sealant has failed. Designing proper joint details with adequate internal drainage can minimise this problem.

Insufficient space allowed for expansion and movement caused by thermal change, deflection of slabs, earthquake and building settlements can also create new paths/ holes/ cracks for leakage.

Consequences

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

1. cracking of components due to moisture movement during wetting and drying and during chemical reaction
2. increase in condensation and growth of mould
3. damage to interior finishing
4. deterioration of joint fittings

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