Tuesday, March 17, 2009
Duct Joining and Sealing with Mastic
Duct sealing can be done at lowest material cost, and with assured complete air tightness, using a two-part tape method, or a simple brush-on or spray-on of mastic. This photo shows one duct element solidly installed with materials I judge to be Hardcast Two-Part: RTA adhesive, and DT 5300 mineral-gypsum-compound-impregnated fiber tape. A two-part joint has alignment strength that is comparable to that with Foilmastic tape, but stable alignment must be achieved by other means, before tape application. The method was easily applied where a small-diameter duct was at rest on blocks. Brush-on mastic has its place where duct joints are not under bending stress. Mastic covering is not suitable where a duct must be lifted for subsequent insulation wrapping.
Hardcast materials are conveniently available at GENSCO.