For Cleaner Application on Longitudinal Seam

Feedback from contractors suggests that some apply the mastic to the longitudinal seam (the Pittsburgh Lock) inside the ductwork rather than outside. The reasoning is that it’s easier to neatly seal the interior duct with a controlled bead of mastic from a caulk tube rather than reaching inside the duct with a chip brush and risking mastic dripping on the interior walls.

We are eager to hear from contractors using cartridges of mastic—what applications is the cartridged sealant being used for?