How do I fix a Pittsburgh seam that was not knocked down and is leaking

Plain-English answer

If the Pittsburgh pocket never got knocked down, the duct may whistle because the mechanical lock was never finished. Sealant over an unfinished seam is a cover-up, not a real correction.

The field fix is to safely access the seam, support the duct if needed, finish folding/closing the pocket lip with the proper hand or air tool, then seal the completed seam per the job standard. If the seam is damaged, kinked, or inaccessible, stop and get direction before beating on it.

Field checklist

• Find the exact length of open or loose Pittsburgh seam.
• Check whether the duct is already insulated, hung under tension, or connected to equipment that could be damaged by hammering.
• Confirm you can close the seam without oil-canning the panel or deforming the fitting.
• Finish the mechanical lock before applying approved sealant.
• Recheck for whistle/leak after correction.

Ask Foreman

Verify before acting

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

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