14.10 Structural silicone Glazing
Structural silicone glazing utilises special grade silicone to adhere and seal glass or cladding materials to the aluminium subframes. In all structurally glazed applications calculations are required to determine the thickness and width of the silicone joint (bite) in order to satisfy load requirements on the frame and glass.
The nominated bite size is attained by correctly positioning and selecting an appropriate structural tape, which is available in varying thicknesses and widths.
During installation, glaziers must ensure the structural silicone being gunned into the joint totally wets both substrates, filling the aluminium to glass void. Temporary retainers may be required to secure the glass in place while the silicone is curing.
One-part silicones cure at about 1mm per day and may require 15 to 20 days to reach full strength after which time temporary retainers can be removed.
Prior to installation, correct cleaning and possibly priming of the aluminium frames and glass is paramount to ensure good adhesion. Refer Section 13.8.
3 and 4 Sided Silicone Structural Glazing
In projects where 3 or 4 sided structural silicone glazing is proposed the glazing must be done in the factory (not on site) under controlled conditions.
In addition the following applies:
- Technical personnel must review all design details and drawings and approve the system.
- Adhesion and compatibility tests must be performed on the substrates.
- A warranty is obtained from the silicone supplier.
- The liabilities for the project are understood by all parties.
- Approval of the system, relevant to the building consent, has been obtained from the Territorial Authority (T.A.).
2 Sided Silicone Structural Glazing
These systems use structural silicone to attach to the
2 mullions or transoms and are often done on site.
Site conditions, cleaning and priming procedures and joint design are critical to the success of these systems.
Silicone Structural Glazing Tapes
Special grade single or double sided glazing tapes are used for these glazing systems and they are normally 6.4mm thick. Refer V1510, V1520, V2510 , VK1826SA, and VK2526 in the table, Section 14.5.
14.11 SILICONE BUTT JOINTS
Silicone butt joints generally consist of either;
- Mitred butt joints with glass meeting at an angle. One or both panes can be mitred to suit the angle required.
- Square cut or 90º passing butt joints are achieved by one pane overlapping the end of the other pane.
- Square cut butt joints with the panes meeting at angles. The square cut ends result in a varying joint gap. This option is often used when the internal angle exceeds 165º as the strength of silicone can be compromised.
- IGU butt joints are normally flashed unless an IGU silicone secondary seal is used, or edge banding is applied to the perimeter to ensure a barrier to UV degrading of IGU sealants.
Generally silicone manufacturers recommend a minimum 6mm glass thickness to ensure adequate silicone bite and adhesion surface for joint strength under load. The joint widths range from 3mm minimum to 10mm with 6mm being ideal.
Note: Laminated glass can
de-laminate at the edge over an extended period from moisture vapour transmission through
the silicone and is not always recommended for butt jointed picture window applications.