Plastic substrates, such as but not limited to phenolic cellulosic composites such as those used in conventional toilet seats, are heated at a temperature and for a time sufficient to degas the substrate, and are then coated with a powder, and heated to cure the powder coating. In a preferred embodiment, a water-based electrically conductive coating is first applied to a phenolic cellulosic composite, and cured while the substrate is heated to degas the substrate sufficiently, such that a subsequently applied powder coating will not suffer from popping during curing. In a preferred embodiment, it is not necessary for the part to be at a temperature at or above the cure temperature of the coating during application of the powder coating in order to avoid popping, provided the substrate has been sufficiently degassed.