Jointing

Sealants

Sealant joints are designed to provide a complete watertight barrier in the form of a single-stage joint positioned towards the panel face.The main types of sealant joint for use with concrete cladding are poly-sulphide (one- and two-part) acrylic and low-modulus silicone. Sealant joints are often used for highly profiled units such as spandrel or parapet panels.

Two-part polysulphide sealants are most commonly used because they have good movement capability and thus can offer greater joint size ranges. However; on large jobs with several mixes the colour of sealant can vary and some manufacturers prefer to use one-part polysulphide, with which the colour is more constant.

Low-modulus silicone (typically Adshead Ratcliffe I 090 or I 099) is used for its good movement capability and longer life expectancy.

Rectangular- or circular-section sealant backing of closed-cell polyethylene foam is used to ensure the correct depth of sealant and to separate it from incompatible materials, which could cause its breakdown (Fig. 1.23).

It must be accepted that the sealant joints will need to be repointed during the life of the building, as the proven life of the best sealants is as yet only 20 years. However; sealants in locations protected from the effects of ultraviolet light and extremes of weather may have a greater life expectancy than those in more exposed positions.

Although most cladding manufacturers continue to use sealant joints, possibly because of their ease of detailing, gasket joints can offer a more stable jointing product, particularly when used as a two-stage joint in conjunction with an air seal.

Ibl m

100 mm + half column £ dimension

50 mm

1.22 Breadth of vertical strengthening rib related to dimension of column: (a) junction without column; (b) junction with column.

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