NOVELTY - Coating composition comprises: (a) a film forming resin comprising (a1) 60-90 wt.% of at least one polyamine containing secondary amine groups prepared by reacting at least one polyamine comprising primary amine groups with an unsaturated dialkyl ester, and (a2) 10-40 wt.% of at least one ester (II), where the wt.% is based on the sum of the weight of (a1) and (a2) in the film forming resin excluding solvent; and (b) a polyisocyanate resin used to cure the film forming resin (a).    USE - The coating composition is useful for coating a substrate for protecting the substrate against rain erosion or solid particle erosion (all claimed).    ADVANTAGE - The coating composition: utilizes (II), thus improving the rain erosion resistance or solid-particle erosion resistance of a coating (claimed); has a low volatile organic compounds (less than 250 g/l); is fast drying; has excellent erosion resistance; is capable of curing to form a coating film on a substrate once it has been applied with no additional heating or exposure to an artificial source of UV radiation; can be used as both a primer coating and as a top coat; is capable of achieving desired dry film thickness (100-300 mu m); and can be directly applied to the substrates.    DETAILED DESCRIPTION - Coating composition comprises: (a) a film forming resin comprising (a1) 60-90 wt.% of at least one polyamine containing secondary amine groups prepared by reacting at least one polyamine comprising primary amine groups with an unsaturated dialkyl ester, and (a2) 10-40 wt.% of at least one ester of formula (II), where the wt.% is based on the sum of the weight of (a1) and (a2) in the film forming resin excluding solvent; and (b) a polyisocyanate resin used to cure the film forming resin (a). The polyisocyanate resin has an isocyanate equivalent weight of 280-840 g/equivalent and a number average molecular weight of 550-2000 g/mole. The components (a) and (b) are present in the coating composition in an amount so that the stoichiometric ratio of isocyanate groups:secondary amine groups is 1:1 to 2.5:1.    X1 = ester functional group of formula (3a) or (3b);    Y1 = 1-10C monovalent alkyl such as 1-6C;    a = 1 or 2;    b = 0-2;    Z1 = C or S;    c = 0 (when Z1 is C) or 1 (when Z1 is S); and    R5 = monovalent alkyl or arylalkyl group having 2-25C.    INDEPENDENT CLAIMS are also included for:    (1) protecting a substrate against rain erosion or solid particle erosion, comprising providing the coating composition, applying the coating composition to the substrate to form at least one coating layer on the substrate, and allowing the coating layer to harden on the substrate at ambient temperature;    (2) a coated substrate, for example a wind blade or its part, where the wind blade or its part is coated with at least one layer of the coating composition; and    (3) use of at least one ester (II) in a polyurea-based coating composition to improve the rain erosion resistance or solid-particle erosion resistance of a coating formed from the polyurea-based coating composition.