Gaskets

Gaskets are lengths of flexible components of various profiles, which may be solid or hollow and manufactured from either cellular or non-cellular materials. They are held in place either by compression or encapsulation into the adjacent building materials and maintain a seal by pushing against the two surfaces (Fig. 16.4). Typical applications include the weather sealing of precast cladding units and facade systems. Within precast concrete, GRP (glass-fibre reinforced polyester) or GRC (glass-fibre reinforced cement) cladding units, the gaskets are typically inserted into recessed open-drained joints. The gaskets therefore act as a rain barrier, but because they

Fig. 16.4 Typical gaskets Iglazing systems

do not necessarily fit tightly along their full length, they can be backed up by a compressed cellular foam wind penetration seals. Gaskets should not be either stretched or crammed in during insertion as they will subsequently shrink leaving gaps or pop out causing failure.

In glazing and related curtain walling systems, gaskets may be applied as capping seals, retained by appropriate profiles within the mullions and transoms; alternatively, the gaskets may be recessed within the joints of the glazing system to give narrower visual effect to the joint. Some glazing gaskets of H- or U-sections are sealed with a zipper or filler strip which is inserted in the profile, compressing the material into an air- and watertight seal. Gaskets and weather-stripping for use on doors, windows and curtain walling are classified by a letter and digit code which defines the use and key physical properties of the particular product, enabling appropriate specification (Table 16.3).

The standard materials for gaskets used in construction are neoprene which is highly elastic; EPDM (ethylene propylene diene monomer) which has better weathering characteristics than neoprene; and silicone rubbers which are highly resistant to ultraviolet light, operate over a wide range of temperatures, and are available in almost any colour. Cruciform section gaskets of polychloroprene rubber are suitable for vertical joints between precast concrete panels.

Waterstops for embedding into in-situ concrete for sealing movement and construction joints are manufactured in PVC or rubber according to the required movement (Fig. 16.5). Sections are available in long extruded lengths and factory-produced intersections. Applications include water-containing structures and water exclusion from basements. Waterstops placed centrally within concrete will resist water pressure from either side, but externally positioned waterstops, not encased below the concrete slab or within permanent concrete shuttering, will only resist water pressure from the outer face.

Proprietary systems offer watertight expansion jointing for horizontal surfaces such as roof car parks and pedestrian areas. Systems usually combine complex aluminium or stainless steel profiles with extruded synthetic rubber inserts. Materials can withstand high loads, with good resistance to bitumen and salt water.

Dry glazing strips are based on elastomeric polymers, typically EPDM or butyl rubber. Usually

Table 16.3 Classification of gaskets and weatherstripping to BS EN 12365-1: 2003

Letter and five number code letter (G or W) digit 2 digit 3 digit 4 digit 5 digit 6

category working range mm compression working temperature deflection recovery after force KPa range oC recovery % ageing %

gasket (G) 9 grades identified 9 grades identified 6 grades identified 8 grades identified 8 grades identified weatherstripping (W) (1 - 9) (1 - 9) (1 - 6) (1 - 8) (1 - 8)

PVC capping strip Fig. 16.5 Concrete waterstop seals the synthetic rubber strip has a self-adhesive backing which adheres to the rebate upstand. With external beading, the dry glazing strip can also be applied to each bead, which is then fixed with suitable compression to ensure a good seal to the glass. The performance requirements and classification for gaskets and weather-stripping for doors, windows and curtain walling are described in the standard BS EN 12365-1: 2003.

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