TinnerFlow™1st YearGREEN · Field ReferenceHalf-Peened Pittsburgh Seam
A Pittsburgh seam has to be mechanically folded tight before it is sealed. If a section is left open, knock it down fully before mastic goes over it.
You use a hand duct hammer to knock down the long Pittsburgh lockseam pocket on a 5-foot section of rectangular duct, but you skip a 1-foot section in the middle because it was tough to reach, leaving the metal lip un-folded.
A Pittsburgh seam has to be mechanically folded tight before it is sealed. If a section is left open, knock it down fully before mastic goes over it. The likely recovery is to check the condition, correct prep/setup if it is within your assignment, and bring the foreman clean information before the work creates rework overhead.
Do not smear mastic over an open seam and call it fixed.
The mechanical lock does the holding; sealant finishes the air seal.
Final direction belongs to the foreman, approved drawings/specs, manufacturer instructions, pressure/material schedule, employer policy, and AHJ/code requirements.