A temporary or protective top layer of hot bitumen mopped over the exposed plies of a built-up roof membrane. It seals the felts against moisture and weather when work is paused before the final surfacing or cap sheet can be installed. This prevents the porous felts from absorbing water, which would cause blistering once the roof is completed.
We're out of cap sheet, so just put a glaze coat on the exposed plies before the rain hits this afternoon.
A glaze coat is usually applied at about half the thickness of an inter-ply mopping, just enough to seal the surface without creating a thick layer that might crack.
Related terms
Cap sheet
The topmost layer of a multi-ply roofing system that protects the underlying membrane from weather and traffic.
Hot mop
Waterproofing built from layers of felt mopped down with hot asphalt, or the act of applying it.
Blister
A raised, trapped pocket of air or moisture vapor within a roof membrane.
Base sheet
The foundational first layer of felt or membrane in a multi-ply roof system.