Abstract: Heat-sensitive porous substrates such as wood, plywood, plyboard, particleboard, fiberboard, cardboard, paper, fiber cement, asbestos cement, concrete and natural stone are coated with a synthetic resin by mixing an aqueous dispersion of 100 parts by weight of a saturated synthetic resin with 2 to 40 parts by weight of an organic liquid consisting of a mixture of 70 to 10 percent by weight of at least one mono ethylenically unsaturated compound having a boiling point of less than 190.degree.C. and 30 to 90 percent by weight of at least one ethylenically unsaturated compound having a boiling point of at least 190.degree.C. in order to swell the resin particles, applying the mixture to the substrate to form a film thereon and hardening the film with UV radiation or with electron radiation to form a hard smooth surface coating on the substrate.