Seal Accessible Duct Leaks with Mastic and HVAC-Rated Tape

A. Finished-Project Specification

Quantity: every joint, seam, takeoff, and register boot identified as deficient in the Project 05 report or by another approved method, sealed with listed duct mastic and, where the approved system permits, listed HVAC-rated foil tape, verified against continued leakage after cure and equipment restoration.

B. Duct Sealing Schedule

Joint / Location	Duct Material	Approved Sealing Method	Verification Method
Trunk-to-trunk joint	From system map / field record	Listed mastic, mesh if required by gap width	Visual continuity, leak-detection method if specified
Branch takeoff collar	From system map / field record	Listed mastic and/or listed foil tape per manufacturer listing	Visual continuity, airflow observation
Duct-board seam	Duct board	Product-specified mastic and mesh system for duct board	Visual continuity, tooling inspection
Register boot to duct	From system map / field record	Listed mastic at the collar connection	Visual continuity, leak-detection method if specified
Register boot to drywall/subfloor	Finish surface at boot perimeter	Compatible approved perimeter-sealing method identified in material takeoff	Visual gap closure, air-noise observation after restoration

C. Material Takeoff

• Sealing materials: listed duct mastic in the quantity required for the total joint linear footage identified in the Project 05 report, listed HVAC-rated foil tape for joints where the approved system permits it, fiberglass mesh reinforcing tape for gaps exceeding the mastic manufacturer's unreinforced limit.
• Fastening materials: mechanical fasteners matching the duct gauge and joint type for any joint identified as loose before sealing.
• Preparation and protection materials: cleaning rags, wire brush or abrasive pad, drop cloths sized to the work area beneath and around each joint.
• Documentation materials: Duct Sealing Worksheet, camera for before-and-after joint photographs.

D. Acceptance Standards

Check	Standard
Surface preparation	Bonding area free of loose dust, rust scale, failed tape, and incompatible sealant, and dry before application
Mechanical fastening	Loose joints fastened before sealant is applied over them
Mastic coverage	Applied to the manufacturer-specified thickness and width with continuous contact and no thin spots or pinholes
Tape application	Applied only where the approved system permits it, to clean dry surfaces, with the required overlap, fully burnished without wrinkles, fishmouths, or bridging
Boot perimeter sealing	Register-boot-to-finish gaps closed using the compatible approved method without blocking required access or drainage
Cure	Manufacturer-specified cure time and conditions met before covering or restoring full operation
Verification	No missed joints, tape lift, mastic cracking, air noise, or continued leakage observed after equipment restoration

E. Preparation and Product Review

1. Review the duct material, service temperature, joint type, insulation, approved sealant, tape listing, and cure conditions. Confirm every product to be used carries a listing compatible with the duct material and service present.
2. Shut down equipment and verify that the duct section is not moving air. Apply the Project 02 shutdown and readiness procedure to this duct section before proceeding.
3. Establish safe access and protect surrounding insulation, finishes, and equipment. Place drop cloths beneath and around each joint scheduled for sealing.

F. Inspection and Leak Marking

1. Inspect the duct for structural damage, corrosion, contamination, wet insulation, or failed supports. Stop work at any joint showing a condition outside the scope confirmed in Project 05.
2. Mark leakage points using visual evidence, previous test data, smoke under controlled conditions, or another approved method. Cross-reference each marked point against the Project 05 deficiency report.
3. Do not seal intentional openings, balancing devices, drains, access panels, combustion openings, or safety components. Confirm each marked point is a joint, seam, takeoff, or boot before proceeding.

G. Surface Preparation and Mechanical Fastening

1. Remove loose dust, oil, rust scale, failed tape, and incompatible sealant from the approved bonding area. Use the wire brush or abrasive pad without damaging the duct surface.
2. Dry the surface and verify it meets product temperature and moisture requirements. Confirm ambient and surface conditions against the mastic and tape manufacturer instructions before applying either product.
3. Mechanically fasten loose duct joints before applying sealant where required. Use fasteners matching the duct gauge and joint type from the fastener schedule.
4. Apply reinforcing mesh at gaps or joints that require it. Use mesh at any gap exceeding the mastic manufacturer's unreinforced limit.

H. Mastic and Tape Application

1. Apply duct mastic to the specified thickness and width over the joint. Measure coverage width against the manufacturer-specified minimum for the joint type.
2. Tool the mastic to continuous contact without thin spots or pinholes. Inspect the tooled surface under the flashlight before moving to the next joint.
3. Use listed HVAC foil tape only where the approved system permits it. Confirm the joint type is one where tape is authorized before applying it.
4. Apply tape to clean, dry surfaces with the required overlap and pressure. Measure overlap against the manufacturer-specified minimum.
5. Burnish tape fully and avoid wrinkles, fishmouths, or bridging. Inspect the burnished tape for full adhesion along its entire length.

I. Boot Sealing, Access Preservation, and Cure

1. Seal register-boot-to-drywall or boot-to-subfloor gaps using the compatible approved method. Confirm the perimeter gap is fully closed without excess material projecting into the register opening.
2. Preserve removable access panels and service connections. Confirm no access panel, damper handle, or service point has been sealed shut.
3. Allow sealants to cure for the manufacturer-controlled time. Record the cure start time and the required cure duration on the worksheet.
4. Reinstall insulation and vapor facing after the seal has passed inspection. Do not reinstall insulation removed for this project's access until the cure period has elapsed and the joint has passed inspection.

J. Restoration, Verification, and Documentation

1. Restore equipment and perform the approved leakage observation. Use the smoke pencil or approved detection method specified for the assigned system.
2. Inspect for missed joints, tape lift, mastic cracking, air noise, or continued leakage. Check every sealed joint identified on the Duct Sealing Schedule.
3. Correct failed areas using the product-approved repair method. Re-clean, re-fasten, and re-seal any joint that fails verification, then repeat the affected observation.
4. Document sealed locations, materials, cure conditions, and inspection results. Complete every entry on the Duct Sealing Worksheet before authorizing Project 07 to begin on this duct section.