Insulating glass units use a primary seal of polyisobutylene against the spacer to stop vapor and a secondary seal of silicone, polysulfide or polyurethane for structure. Desiccant in the spacer keeps the cavity dry. When the seals fail, moisture enters and the unit fogs between the lites. Glazing sealants must be compatible with the unit's edge seal.
Six IGUs are fogged on the south side, seal failure, get the sizes and order replacements.
Also heard as
- insulating glass
- IG unit
Related terms
Lite
A single pane or unit of glass in a window, door or curtain wall opening.
Butyl
A rubber-based sealant or tape with very low vapor transmission but little movement capability.
Compatibility test
A lab check that a sealant and the materials it touches do not react, discolor or lose adhesion together.
Setting block
A small rubber block under the bottom edge of the glass that carries its weight and keeps it off the frame.