A composition contains: (a) a first organopolysiloxane with an average of 2 or more mercaptoalkyl groups per molecule and that is free of alkenyl functionality; (b) a second organopolysiloxane with an average of one or more alkenyl group and one or more alkoxy group per molecule; (c) a tetraalkoxy silane; (d) an ultraviolet light photoinitiator; and (E) a condensation catalyst; where the concentration of the first and second organopolysiloxanes are such that the molar ratio of mercaptoalkyl groups to alkenyl groups is in a range of 0.4 to 3.0.