Durability of field-molded sealants in joints is determined by the degree of mechanical and chemical deterioration that occurs during service. The mechanical deterioration of sealants in working joints is the most critical factor of durability.

Sealants used in working joints of curtain walls are subjected to thermal movements which cause fatigue of the sealants and lead to their failure. In joint design, fatigue of the sealant is related to the concept of movement capability. However, since the basis for obtaining movement capability is questionable, the movement capability may be overestimated, often resulting in leakage at joints.

The authors introduced repetitive compression-extension tests and quantitatively determined the fatigue process of a sealant based on resilient energy. A rational method of obtaining the movement capability of sealants consequently has been developed.