Case 4

Good Practices

Water barrier between floors:

Horizontal gutter which separates each floor and drains and eventual water penetration to the outside characteristics water barrier. In some systems there is a second barrier under the slab in order to drain any eventual water leaking.

Adopting pressure equalizer system:

The presence of water, hole and pressure differential are the 3 key factors of leakage. Thus, by eliminating one of the above conditions, the leak will not occur. Rain cannot be eliminated. It is also difficult to close all the myriad of joints and gaps in a curtain wall with gaskets and sealants. The easiest way is to eliminate the pressure difference at the level of external joint so that the internal joint is never in contact with water and therefore a small gap or failure of sealant at the internal joints/gaskets can never produce water leaks but only small air losses when it is windy. (Figure 3)

Using structural sealant:

Sealant failure is one of the major causes of water leakage through curtain walls. Due to the mismatch of physical and chemical properties (coefficient of thermal expansion, cohesion, adhesion,. elasticity) of sealant and its substrates, structural sealant are not widely used to accommodate thermal movement. They have been promoted by the trend to structurally glazed curtain walls where glass is bonded to the frame with special silicones.

The effects of capillary action can be foiled by breaking possible capillary paths. This can be achieved by having grooves within the joints or by widening joint interfaces. (Figure 4)

As joints expand and contract or experience shear movement, the shape of the sealant changes, the magnitude and type of stress also change because the sealant may be either in compression, expansion or shear. Thus, in designing joints, it is vital that the proper width-to-depth ration may be specified so that the width of the joint is consistent with the capability of the sealant to endure daily and seasonal changes for prolonged periods. (Figure 5)

The table provides a guide to the width-to-depth ratio relationships for polysulphide sealants- once the width has been determined.

The amount of movement in a joint is dependent on the length and composition (the coefficient of linear expansion) of a panel section and the temperature gradient that causes the movement. For sealants with less movement capability, wider joints are needed. Otherwise, sealant failure will occur.