Provided herein is an additive manufacturing method of making a three-dimensional object comprising polyurea, comprising: (a) dispensing a one part (1K) dual cure resin into a stereolithography apparatus, the resin comprising or consisting essentially of a photoinitiator, a reactive blocked polyisocyanate, and optionally a polyepoxide, the reactive blocked polyisocyanate comprising the reaction product of a polyisocyanate and an amine or hydroxyl (meth)acrylate or (meth)acrylamide monomer blocking agent; (b) additively manufacturing from said resin an intermediate object comprising the light polymerization product of said reactive blocked polyisocyanate; (c) optionally cleaning said intermediate object; and (d) reacting said polymerization product in said intermediate with water to generate polyamine in situ that sequentially reacts with the remainder of the polymerization product to form urea linkages and thereby produce a three-dimensional object comprising polyurea. One part (1K) dual cure resins useful for the method are also provided.