Duct sealing mastic application involves brushing or spraying specialized sealants on ductwork joints and seams to eliminate air leakage and maintain system efficiency. Mastic sealants permanently cure to form airtight seals without the brittleness of caulk or duct tape.
Product Specifications
HVAC mastic is typically water-based acrylic or polyester material meeting ASTM C834 standards. Products cure within 24-48 hours and accommodate thermal expansion of 5-10 percent. Application thickness should be 1/8 to 3/16 inch. Standard coverage rate is 40-50 square feet per gallon. Mastic remains flexible after curing, preventing cracking from ductwork movement and temperature fluctuations.
Application Procedure
Surfaces must be clean and dry; dirty ducts reduce adhesion by 30-40 percent. Joints, seams, and connection points receive mastic application using stiff brushes or spray equipment. Fiberglass mesh reinforcement embedded in mastic provides additional strength for critical joints. Proper sealing reduces ductwork leakage from 15-30 percent to less than 5 percent, improving system efficiency by 10-15 percent and reducing energy costs significantly. Professional application requires skill to achieve uniform coverage and prevent over-application.