PURPOSE: To produce a backing plate for external finishing which can be directly coated on a wall coating material and has a sound insulating property by forming a waterproof layer on a base plate then forming a sound-insulating coating layer mixed with a fluid material, inorg. powder and heavy-duty material powder.

CONSTITUTION: A sealer consisting of a plastic, latex, etc. is coated on the surface of an inorg. or org. plate-shaped base plate 1 to form a waterproof layer 2. A sound-insulating coating prepd. by mixing a plastic, latex or bituminous material, inorg. powder having ≥1 specific gravity and heavy-duty material powder having ≥4 specific gravity to ≥2 specific gravity is coated on the layer 2 to form a sound-insulating coating layer 3. The backing plate produced in such a way is directly applicable on a wall coating material and has a high sound insulating property.