PURPOSE: To provide an undercoating capable of shortening processes and coloring in any tones, by incorporating a partially crosslinked nitrile rubber, a synthetic resin, a hard resin, an inorg. filler, an antisagging agent, and a solvent.

CONSTITUTION: 6W15wt% (solids) partially crosslinked nitrile rubber, 24W37wt% (solids) synthetic resin compatible with said nitrile rubber, 6W13wt% hard resin, 28W48wt% inorg. filler, 2W6wt% antisagging agent, and a necessary amt. of solvent having a concn. of hydrogen bond of 4W6 and a solubility parameter of 8W10 are mixed together. Said nitrile rubber is used to improve pitting resistance, soundproofness, oil resistance, and low-temp. resistance and to prevent stringing in spray coating. Said synthetic resin is used to improve adhesion to substrates, rustproofness, and resistance to water and salt water. Said hard resin is used to improve film dryability and film strength.