Comparisons of Silicone and Urethane Sealant Durabilities

A two‐year aging study was presented for four sealants: a low‐modulus silicone, a medium‐modulus silicone, a one‐part polyurethane, and a two‐part polyurethane. A specimen, with red granite substrates, is used. The four aging exposures are: ordinary room conditions; outdoors in Houghton, Michigan; outdoors near Hilo, Hawaii; and aging in a Q‐Panel (QUV) weathering unit. Following an initial six‐week cure, room‐ and outdoor‐aged specimens are tested at zero‐, six‐, 12‐, and 24‐month intervals. The QUV‐aged specimens are tested after 0, 500, 1,000, and 5,000 hours. In the postaging tests, specimens are given 20 displacement cycles at the sealant's rated movement capacity and elongated to failure. Reported data include nominal stresses at 25%, 50%, and 100% elongation, the ultimate tensile strength, and the corresponding elongation. Additionally, observations are given for surface cracking and dirt pickup. Adhesion to the substrates is good for all four sealants. Results of a pilot study combining QUV exposure with a displacement cycle are also reported. The overall findings indicate that the silicones' performance is superior to that of the urethanes.