Why does a half-peened Pittsburgh seam leak

Plain-English answer

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.

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Use this as training guidance. Foreman direction, approved drawings, project specs, manufacturer instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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