Treat grease/special exhaust as red-zone work: using normal mastic on grease duct.
High-risk starter answer - treat grease duct, hood exhaust, kitchen exhaust, lab exhaust, and special exhaust as red-zone work. Stop before cutting, drilling, fastening, patching, sealing, relocating, or changing anything until the foreman confirms the approved detail and who is allowed to do that work.
Ask any time grease/special exhaust involves access, weld, wrap, slope, clearance, penetration, contaminant, or support questions.
Watch out
Do not assume normal galvanized duct rules apply.
Check
Confirm whether this is grease duct, kitchen exhaust, lab exhaust, industrial exhaust, or normal exhaust.
Check the approved drawings/spec/submittal.
Look for cleanout/access, clearance, enclosure/wrap, weld/seal, slope/drainage, and inspection requirements.
Steps
Confirm the system is grease, kitchen exhaust, industrial exhaust, dust, or chemical/fume exhaust.
Check approved detail for material, access, cleanouts, joints, wrap, slope, and support.
Identify hot-work or fire-watch requirements.
Focus on the actual issue: using normal mastic on grease duct.
Photograph or mark the condition if someone else needs to approve it.
Say this to your foreman
In Grease Duct, Kitchen Exhaust & Industrial Exhaust, I'm looking at: Using normal mastic on grease duct. What should I verify before I cut, drill, seal, cover, move, or install?