A novel sealant testing device was used to continuously monitor the mechanical properties of a one-part silicone sealant for movement cycles initiated from 10 to 168 h after sample creation. These cure times fall between the proposed RILEM TC-139 technical recommendation of 5 min and the ASTM C719 standard of 21 days. At 10 h of cure, enough crosslinking occurred before testing such that neither the overall movement history of the sample nor the deformation step shapes affected subsequent curing of the sealant. A critical parameter for sealant performance appears to be the extent of cure at the onset of movement. POLYM. ENG. SCL, 50:113-119, 2010. (C) 2009 Society of Plastics Engineers