Do not force a gapped corner together with hardware. Do not treat mastic as the primary fix for a bad flange fit. Do not assume random fasteners are the normal field fix.
Check
Flanges meeting close?
Duct level and square?
Corners seated?
Gasket not bunched?
Is hardware/shop method correct?
Steps
Flanges meeting close?
Duct level and square?
Corners seated?
Gasket not bunched?
Is hardware/shop method correct?
Say this to your foreman
This TDF corner has a gap before it is locked down. Do you want me to re-square the duct, reset the corner, add the proper cleat/fastener, or stop for shop/foreman direction?