PURPOSE: To obtain a specified thickness and a good water shielding property by placing two sheets of reinforcing base fabric on a face to be waterproofed and spraying a specified waterproofing agent over the fabric to impregnate the fabric to the rear face of the lowermost layer.

CONSTITUTION: Two sheets of the reinforcing knit fabric having ≥50% longitudinal breaking elongation, 2-10mm thickness and 0.08-0.16g/m3 density are placed on a face to be waterproofed, and a delayed-coagulation waterproofing agent having 5,000 to 30,000cps viscosity at 20°C under pressure before coagulation and needing 10-60sec after the start of coagulation until 100,000cps is reached is sprayed over the fabric to impregnate the fabric to the rear face of the lowermost layer. Consequently, a waterproofing layer excellent in workability and water resistance and having a specified thickness is obtained.