the invention relates to a process for the production of a very thick , self - supporting , z - shaped plastic laminate , starting from a plurality of kraft papers imbued with phenolic resin , possibly with a superposed sheet of decorative paper imbued with melaminic resin , said papers being pressed in two successive processing phases ; in the first phase the pressure is kept at a minimum level , while the temperature of the papers rises up to the temperature of polymerization of the resins , and in the second phase the temperature keeps at a substantially constant level while the pressure rapidly increases , at least initially .