The joint between the vertical mullions is also an expansion joint for curtain wall components. These joints must be designed on a job-by-job basis.
The rails ( horizontal mullions 0 are then attached to the vertical mullions to create frame openings, one frame opening for the vision area to receive an insulating glass unit ( IGU0 and one frame opening for the spandrel area to receive the vision panel cover (to hide the floor edge, perimeter heating equipment and ceiling plenum areas).
Stick system is widely used in the Gulf region, where you can see all the glazing from the outside with silicone joints with the combination f slim narrow framing is only visible from inside.
The stick system can be constructed airtight and resistant to water penetration. When the aluminium frames are assembled, a corner block is installed at the junction of the vertical mullion and rail. This corner block separates the glazing cavity of the sealed units from the glazing cavity of the spandrel area. It acts both to divert water into the sill cavity of the rail and as a compartment seal for pressure equalization performance.
The spandrel glass is usually monolithic heat strengthened glass with a coloured coating( frit) and polyester film to pacify the spandrel glass and to closely approximate the colour or the tint of the vision units. The spandrel covers may also be aluminium, stainless steel and copper panels. In the last few decades, granite panels, as well as sealed units, have been installed in the spandrel areas of the curtain wall systems.