An improved process for manufacture of polymer coated composite substrates is described. a coated composite substrate is prepared in the press by applying a layer of a primer coating composition to the surface of a compressible mat comprising fibers and/or particles and a resin binder. The primer coating composition is formulated preferably as a fast setting polymer latex capable of forming a chemically crosslinked polymer matrix when applied to the surface of a compressible mat. A thermosetting top coat composition can be applied directly over the wet primer coating composition before heat-processing the mat to improve surface quality and release characteristics. Compressing and heating the coated mat produces a primed composite substrate directly out of the press.