40 Years of Outdoor Weathering: A Real-World Study of Silicone vs Alternative Chemistries

Ensuring the long-term performance of sealants is critical to the durability of any construction project. Buildings must withstand the elements year after year, making material and sealant selection essential.  

With countless options and varying chemistries available, choosing the right sealant can be challenging. So how do you identify solutions that truly stand the test of time?

40 years ago, we launched one of the longest-running studies on silicone performance ever, conducted at the Atlas Weathering Test Site in Miami, FL, to answer that very question.  

The 22-acre Atlas Weathering Test Site has over 75 years of experience testing paints, coatings, textiles, plastics and various other products. It’s the first approved Test facility for The Cool Roof Rating Council (CRRC)’s Product Rating Program.  

A team of researchers evaluated the durability of various sealants under extreme real-world conditions. This four-decade-long study provides unparalleled insight into how different chemistries withstand exposure to high humidity, intense UV radiation, and the tropical storms of Florida—one of the most challenging environments for material durability testing.

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Silicone vs. Alternative Chemistries: A Long-Term Review

The study compared silicone, polyurethane and acrylic chemistries, assessing their adhesive bond, surface condition, flexibility, resilience, and change in hardness after prolonged exposure to replicate real-world conditions. These included high levels of ultraviolet radiation, humidity and temperature in a subtropical environment.

The test panels featured square pieces of glass and painted aluminum mounted on outdoor exposure racks facing south at a 45° angle to the horizon. The sealants have been checked at 22, 30, and 41-year periods to assess their appearance, flexibility, hardness and adhesion to determine the effects of ageing over time.

The study used sealants from six different manufacturers, with nine of the original thirteen products used still commercially available at the end of the 40-year test.

The sealants were tested for:

• Adhesion (ability to maintain long-term adhesive bonding)
• Flexibility (capacity to be easily bent, without breaking or cracking)
• Resilience (defined as the % recovery to the original shape within 5 minutes of being bent 180 degrees and then released)
• Toughness
• Hardness change

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Results and Observations

After 40 years, the test revealed the following:

• In all cases but one, silicone outperformed polyurethane and acrylic in overall durability under weathering conditions.
• Acetoxy silicone sealants ranked highest for durability at the test site, demonstrating superior resistance to aging and environmental stress.
• Acetoxy silicone sealants showed near-instantaneous 100% elastic recovery, meaning they rebounded immediately after stress, unlike alternative chemistries.
• The general overall surface condition of the silicone products was better than the non-silicone products.

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Adhesion, Flexibility & Elastic Recovery Results

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Adhesion vs. Cohesion: What Matters Most?

One critical factor in sealant performance is how failure occurs:

• ‍Cohesive failure happens within the sealant itself, meaning the material remains bonded to the substrate but splits internally.
• ‍Adhesive failure means the sealant loses its bond to the surface, leading to potential leaks and performance issues.

All nine silicone sealants showed cohesive failure rather than adhesive failure in the study after 20, 30 and 40 years. This is a positive result.  

For long-lasting weatherproofing, a sealant should be stronger adhesively than cohesively, ensuring it remains securely bonded to surfaces while flexing with the movement of the structure.

Delivering Solutions for a Sustainable World™

Momentive has a long history as leaders in silicone technology, dating back to the 1930s.  

Through our company lineage (In 2006, Momentive purchased GE Advanced Materials), we were the first to market with silicone technologies across a range of industries, including construction. We have more than 80+ years of experience in the research, development, and production of silicone and specialty materials.

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Products—Key Features & Typical Benefits:

• Room temperature cure; neutral alkoxy cure type.
• Flexible application.
• Rain-ready within 30 minutes.
• Primerless adhesion to many substrates.
• Excellent adhesion after extended aging.
• Flame retardant: UL94HB certified (File No. E56745).
• Wide operating temperature range from -50 to +200 ℃.

Performance results will vary depending upon a number of process-related factors. Prospective customers should rely solely upon their own evaluative techniques to determine what processing parameters are attainable and optimal to their specific needs.

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