Prepregs for use in building lay-ups of composite materials

A prepreg assembly comprising

• a prepreg comprising a fibrous reinforcement comprising reinforcing fibers and a prepreg resin comprising a thermoset resin that is curable at a curing temperature, said prepreg having a surface that has tack and comprises said prepreg resin and wherein the surface mass of said reinforcing fibers is from 80 g/m2 to 4000 g/m2, and
• a scrim located on said surface of the prepreg, said scrim comprising a plurality of thermoplastic strands that each have a cross-sectional diameter of 100 microns to 1000 microns, said thermoplastic strands forming form a grid of parallelograms comprising warp direction strands and strands that are crosswise to said warp direction strands, said warp direction strands being spaced from 3 to 60 millimeters from each other and wherein said strands that are crosswise to said warp direction strands are from 3 to 60 millimeters from each other, said thermoplastic strands each having a cross-sectional diameter and a circumference which is determined by said cross-sectional diameter, wherein less than half of the circumference of each of said thermoplastic strands is coated by said prepreg resin and more than half of the circumference of each of said thermoplastic strands is not coated with said prepreg resin and wherein said prepreg has sufficient tackiness to hold said scrim in place on the surface of said prepreg.