A configuration in which adjacent glass edges meet at an open or sealant-filled joint without a conventional mullion directly covering that joint.
GlassRenu · Educational illustration
Meaning and boundaries
A butt joint does not automatically provide structural attachment or make adjacent panels act as one structural lite.
Why it matters in glass restoration
Exposed edges, unsupported spans, sealant joints, and localized movement make perimeter damage or aggressive treatment a referral condition.