This type of joint normally incorporates a neoprene-extruded section; because they are factory produced, they are not so dependent on the site operative for their successful application. As an alternative to neoprene, ethylene propylene diamine monomer (EPDM) has better inherent resistance to oxidation attack and subsequent ageing. However; its drawback is poor resistance to attack from lubricating oils and various solvents. EPDM's ability to recover from compression is also less than that of neoprene. Although it is possible, according to their formulation, to obtain rubbers with good or bad tear resistance in both neoprene and EPDM, generally speaking EPDM has less resistance to tearing than neoprene, and thus is less easy to handle on site.
Site bonding of neoprene sections is now quite common for crossover joints. For example, the neoprene gasket joint used at the Herman Miller factory (Figs 3.19 and 3.20) is a simple glazing technique for both vertical and horizontal joints. A top-hat section is screwed into an aluminium carrier system, which in turn is supported by the main framing.
A continuous gasket is then pushed into this top-hat section. At parapet level the neoprene vertical joint changes to a narrow mastic sealant, because of difficulties in carrying the top-hat section over the curved jointing profile.
Neoprene gaskets work best when they are compressed within the joint, normally on the back side of the panel edge profile. A simple compressible gasket using timber edging pieces with GRP panels was developed for Teesside Polytechnic (architects: Basil Spence & Partners) (Fig. 3.21), for use with panels I m x I m. A more complicated gasket joint was developed for Mondial House (Hodge, 1968) (Fig. 3.22), which uses a combination of a neoprene baffle, a PVC back channel and a strip sealant under compression from a back plate.The joint was tested successfully by Yarsley Laboratories to BS 4315, simulating I 8.75 cm of rain per hour at a wind speed of 56-64 km/h.This very sophisticated joint combines the principles of an open-drained joint with that of a labyrinth joint. As a result of this experience at Mondial House, Anmac Ltd developed its own 'patented'two-stage mechanical joint called LSB. This had the advantage that the jointing product is under compression and hidden from ultraviolet light.
This type of joint (see Fig. 1.24 for an example in concrete cladding) is not in widespread use with GRP panels.This may be because of the difficulties that can be experienced in casting the necessary depth of baffle groove. Other problems have been experienced in fixing the baffles at the top of the panel to prevent them from sliding down the groove. Open-drained joints at HMS Raleigh, Plymouth (Fig. 3.24), incorporated a bridging plate at the top of the joint in an attempt to stop the baffle from slipping.
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