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Cladding and Curtain Wall Construction 459
Neoprene compression
gasket pressed into joint
Backing strip
and sealant
GRC panel
Gasket
joint
Backing strip
and sealant
Gasket
Rebated
horizontal joint
Figure 7.39 Gasket joint.
7.39 is that the deep rebate will provide a degree of protection against rain running down
the building face that a parallel flat face will not, where a similar vertical joint will provide
protection from one direction only.
Open drained joint
Open drained, vertical joints are used for the larger GRC or rock-based panels where it is
not practical to form the narrow, accurately fitted joints necessary for both mastic and
gasket jointing. Plastic channels are cast in a chase in the vertical edges of panels, as illustrated
in Figure 7.40, inside which a plastic baffle is hung as a loose fit. The inside joint
between panels is sealed with a backing strip and mastic sealant joint.
The loose baffle acts as a first line of defence against wind-driven rain, most of which
will run down the baffle. Because the baffle is a loose fit, there will be a degree of wind
pressure equalisation on each side of the baffle, which will appreciably reduce wind pressure
on rain that may find its way past the baffle. The advantage of this joint is that it allows
for movement of the panel, inaccuracies in manufacture and assembly, and acts as a reasonable
barrier to wind-driven rain. This open joint acts in conjunction with a rebated,
overlapping horizontal joint which is mastic sealed on the inner face. It is accepted that
this joint is not a complete barrier to rain. The effectiveness of the joint depends on the
degree of exposure and the surface finish of the panels. Smooth faced panels will tend to