Water-based mastic is brushed or troweled onto joints, with fiberglass mesh tape bridging larger gaps, and cures into a flexible, permanent seal that far outlasts cloth duct tape. As a verb, mud the joints means seal them with mastic. Inspectors and energy raters look for it at every takeoff, boot and plenum connection.
Heard on the job
Mud every takeoff and the boots before the insulation goes on, the leakage test is Thursday.
Also heard as
- mastic
- duct mastic
Related terms
Duct leakage
Air lost from supply ducts or pulled into return ducts through gaps at joints, seams and connections.
Tin knocker
Jobsite nickname for a sheet metal worker who fabricates and installs ductwork.
Plenum
A box on the supply or return side of an air handler that feeds or collects several ducts, or a ceiling cavity used as a return path.