This invention describes a process to coat a substrate by a polymer film, stable in humid environment or when immersed in an aqueous solution. This universal process is applicable to any kind of polymer (natural or synthetic, reticulated, branched, star-shaped, copolymers, non-charged polymers or polyelectrolytes, fluoropolymers…) and any substrate (metallic, mineral, organic, ceramics, inorganic and organic composites) of any shape (flat, polyhedra, platelets, wafers, rings, curved and saddle-shaped, hollow tubes, rods, and cylinders) with any kind of interface (smooth, rough, porous, amorphous or crystalline, regular or irregular structures).