40-Year Research On Silicone Sealants: A Comparison With Alternative Chemical Formulations

As structural glazing systems grow more elaborate and sophisticated, and as requirements for durability and sustainability keep increasing, the service life of building materials has become more critical than ever before.

Sealants are vital to the long-term functionality and weather resistance of curtain walls and glazing systems. The choice of an appropriate sealant can determine whether a building enjoys decades of low-maintenance operation or faces expensive repairs and system breakdowns.

In truth, it has long been recognized that "the sealing material is usually the most important component of the joint assembly that influences durability"-a point highlighted in the 1966 version of Time Saver Standards (Figure 1).2

Yet which chemical formulation can stand up to the test of time?

This paper presents the outcomes of one of the longest-running studies on glazing sealants-a 40-year outdoor weathering evaluation that compares silicone-based sealants with those made from polyurethane and acrylic chemistries. Carried out at the Atlas Weathering Test Site in Florida, this real-world research offers valuable guidance for architects, material specifiers, building envelope engineers, and contractors who aim to make well-informed material choices that have an impact on all aspects of the building envelope.

The study focuses on the performance of silicone formulations, particularly acetoxy and alkoxy types, by evaluating key characteristics such as adhesive strength, cohesive strength, flexibility, toughness, resilience, hardness, surface condition, and long-term durability when exposed to extreme heat, ultraviolet (UV) radiation, and high humidity. It also provides comparative data to support specification decisions.

The Importance of Long-Term Performance Data

Modern buildings are designed to last for many decades, and some even for centuries. For this reason, it is essential for contemporary materials to have long-term performance data under real-world conditions. While accelerated aging tests offer useful information, they cannot replace the insights gained from long-term outdoor exposure testing.

To address this need, GE Silicones (now known as Momentive Performance Materials) initiated one of the world's most ambitious sealant weathering studies in 1983. The study involved applying various sealant chemistries to test panels and exposing them to Florida's tropical climate over an extended period.

The 9-hectare (22-acre) Atlas Weathering Test Site-the first testing facility approved by the Cool Roof Rating Council-provided an ideal setting for the research. Florida's climate, characterized by high humidity, intense UV radiation, and frequent tropical storms, is among the most demanding natural environments for testing the durability of glazing sealants.

Key Findings: A Summary

Following 40 years of outdoor exposure, the results were clear: silicone sealants consistently outperformed polyurethane and acrylic sealants in terms of durability, elastic recovery, and surface integrity, proving their long-term performance capabilities. Although the study focused specifically on sealants, these same chemical formulations are widely used in curtain wall and glazing applications.