The changes in the physical properties of three different commercial silicone sealants used in structural glazing applications were monitored as a function of various aging factors. The variables included, simultaneous exposure to ozone and moisture in which the pH of the moisture was maintained at discrete levels of 3 and 11. The extremes of the pH range represent recorded values for acid rain (pH = 3) and basic cleaning solutions (pH = 11), respectively. A second portion of the study involved studying the effect of loading on the sealant performance. The experimental coupons were cut from cast sheets of DC-790, DC-995, and DC-983. An Instron tester was used to measure the changes in the engineering properties such as Young＇s modulus, relaxation time, and ultimate tensile stress of the test samples as a function of time of exposure to the different variables. Unexposed samples, kept at ambient laboratory conditions, were used as the control. Results of these tests indicate that the Young＇s modulus of the samples decreases during an initial period as a result of their exposure. After this initial decrease the sample moduli showed a steady increase with time. Surface cracking was observed during the initial period, even though the moduli continued to increase. Moreover, the add and ozone appear to act synergistically in the deterioration of the sealant. Samples exposed to the higher pH level did not show this kind of behavior. The effect of tensile loading on the sealant was significant only for DC-983, the high modulus formulation. This was perhaps because of the creation of high stress centers. The medium modulus material exhibited good resistance to the synergistic effects causing deterioration. Ozone resulted in discoloration, softening, and change in structure in the low modulus formulation. Although the ozone did not react aggressively with silicone, its slow attack or degradation should still be of concern. In spite of the use of inhibitors, severe and acute cracks appeared on the surface of the rubber material at angles of ninety degrees across the line of tension. It is hoped that these accelerated test results can lead to more informed decisions concerning silicone sealant life following their exposure to ozone and acid precipitation.