A process for forming a corrosion resistant high-build type coating film, which comprises (i) a step of priming on a substrate a coating composition comprising (a) 100 parts by weight of a mixture composed of from 99.9 to 60% by weight of a vegetable oil and/or a phthalic alkyd resin, and from 0.1 to 40% by weight of tricyclodecene and/or its derivative, and (b) from 1 to 500 parts by weight of at least one member selected from the group consisting of an oxyacid salt, and metal lead and its oxide and salt, followed by drying it to form a prime coat, and (ii) a step of applying thereon a radical-polymerizable and oxidation-polymerizable, room temperature curing type solventless coating composition, and polymerizing it to form a cured coating film.