What do I do when mastic applied over dirty/oily duct?
Sealing, Leakage, Mastic & Pressure Testing.1 field-polished — seal/test detail check
Do not seal over oil, dust, or dirt. Clean the metal first so the approved sealant can actually bond.
Field checklist
- Stop sealing that joint.
- Wipe/clean the duct surface per site/product direction.
- Let wet areas dry before sealing.
- Reapply only after the metal is clean and tight.
- Ask before trying to hide a dirty joint with extra mastic.
Ask foreman
This joint is dirty/oily before sealing. Do you want it cleaned and resealed with the approved method?
Do not
Do not smear mastic over dirty, oily, wet, or loose surfaces.
Why it matters
Sealant sticks to clean metal and approved surfaces. Dirt or oil can cause peeling, leakage, and failed test/inspection.
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