Most of the time when you spray gel coat on a surface that will be the final surface you add wax to it. The wax rises to the surface and blocks air from reaching the surface of the gel coat. You get a better finish with wax than by spraying PVA on the surface. In my experience PVA is used as a mold release agent for potentially hard to release parts. It is sprayed on the mold after the mold is waxed.