Weathering affecting adhesive joints

Epoxy adhesives and sealants are generally not significantly affected by simple outdoor weathering. However, there are certain circumstances that could affect the permanence of joints exposed to outdoor service, ft is important that these be considered early in the design of the adhesive joint and selection of materials. 

Adhesives exposed outdoors are affected primarily by heat and humidity. Thermal cycling, ultraviolet radiation, and cold are relatively minor factors. Structural adhesives, when exposed to weather, rapidly lose strength during the first six months to a year. After two or three years, the rate of decline usually levels off, depending upon the climate zone, polymer, adhesive, and stress level. The following are important considerations when designing an adhesive joint for outdoor service ... 

Water must be considered a dominant factor in determining the permanence of adhesive-bonded joints in most weathering service environments. The structure may be affected or involved in a variety of ways, depending on whether water can penetrate into the adhesive structure itself to produce significant property changes, or move via some pathway to reach the interfacial areas and debond the adhesive. 

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