Static field route #19643

What do I do when part of a Pittsburgh seam was not knocked down?

Rectangular Duct Assembly: S-and-Drive✅ FIELD REFERENCEField answer expansion

📖 Verified core answer

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.

Open in Field Rescue Open category

Field verification checklist

Run your hand/eyes down the full seam length.
Find any lip that is still standing proud.
Support the duct body while peening the seam.
Knock the raw edge flat over the pocket lip.
Seal only after the mechanical seam is closed.

Ask foreman

You can't leave a gap in a Pittsburgh seam. Grab the blocking hammer and knock that center section down completely flat over the pocket lip before you swipe it with bucket seal.

Text to foreman

Route options

A Correct prep/setup only if the fix is within your assignment and the approved method is clear.

B Hold and document if it affects safety, structural support, rated assemblies, airflow, access, tools, material condition, or another trade.

C Bring the journeyman/foreman the location, what you checked, and what decision you need before the crew loses time.

Do not do this

Do not smear mastic over an open seam and call it fixed.

Why this matters

The mechanical lock does the holding; sealant finishes the air seal.

Final verification

Use this as field training guidance. Final direction still comes from the foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, pressure/material schedule, and AHJ/code requirements.

Search helpers: pittsburgh seam not knocked down pocket seam leak helper hammer