NOVELTY - The prepreg (2) comprises a fibrous reinforcement layer (4) partially impregnated with a matrix resin (6) having a first viscosity and a coating (10) of a wet resin having a second viscosity on a first side of the fibrous reinforcement layer, a first removable flexible film that acts as a barrier to ultraviolet radiation on a second side of the fibrous reinforcement layer, and a second removable protective flexible film covering the coating of wet resin. The first viscosity is higher than the second viscosity. The matrix resin and the wet resin are curable by ultraviolet radiation.    USE - The prepreg is useful for bonding a cured prepreg to a surface of a substrate for repairing a damaged surface of the substrate such as a fiber reinforced matrix resin composite material and a leading edge of a wind turbine blade (all claimed).    ADVANTAGE - The prepreg is water-proof, can be simply manufactured with high quality and durability, is capable of efficiently, rapidly and economically repairing the damaged surface of the fiber reinforced matrix resin composite material, and provides good adhesion and durable repair to the substrates.    DETAILED DESCRIPTION - The prepreg (2) comprises a fibrous reinforcement layer (4) partially impregnated with a matrix resin (6) having a first viscosity and a coating (10) of a wet resin having a second viscosity on a first side of the fibrous reinforcement layer, a first removable flexible film that acts as a barrier to ultraviolet radiation on a second side of the fibrous reinforcement layer, and a second removable protective flexible film covering the coating of wet resin. The first viscosity is higher than the second viscosity. The matrix resin and the wet resin are curable by ultraviolet radiation, and comprise a thermosetting resin having ethylenically unsaturated copolymerizable monomers with a photinitiator. The wet resin coating has a thickness of 100-400 mu m. The viscosity of the wet resin is 130-1000 Pa.s at a shear rate of 1s-1 measured at a temperature of 20 degrees C. The matrix resin has a viscosity of 2x 104 to 1x 106 Pa.s at 20 degrees C. An INDEPENDENT CLAIM is included for a process for bonding a cured prepreg to a surface of a substrate.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a prepreg.    Prepreg (2)    Fibrous reinforcement layer (4)    Matrix resin (6)    Coating of a wet resin (10)    Removable flexible film (11)    Fiber. (12)