The 82-story-tall Amoco building (now Aon Center) in Chicago, Illinois, was originally clad with approximately 44,000 marble panels. After the marble lost significant strength from exposure to the weather, all of the marble panels were removed and replaced with granite panels. During the design of the replacement granite panels, two mock-ups consisting of granite, polyurethane sealants, and silicone sealants were constructed to assess the staining potential of the sealants. The mock-ups were placed on the roof of a two-story building in Northbrook, Illinois, facing south. One of the mock-ups was oriented at an angle of approximately 30° from horizontal and the other mock-up was oriented vertical. After approximately 18 months of exposure to the weather, plasticizer migration from the silicone sealants stained the granite. Consequently, a polyurethane sealant was selected to seal the granite panel joints. After the mock-ups were exposed to the weather for approximately 30 years, plasticizer migration from the silicone sealants into the granite was evident, confirming that the plasticizer migration is permanent, and surface crazing and limited reversion occurred in the polyurethane sealants. Orientation of the mock-up facing south at an angle of 30° from horizontal accelerated the effects of the weather on sealants in the mock-up.