PURPOSE: To obtain a water impervious sheet which can be manufactured at any desired thickness by coating high water absorbing inorganic particles having a predetermined particle diameter to the water permeable sheet having a predetermined strength with the specified adhesive showing the elasticity at an ordinary temperature, and forming a sheet as a plurality of layers which consists of multiple sheets coated with the high water absorbing inorganic particles.

CONSTITUTION: High water absorbing inorganic particles 2 are distributed between an upper and a lower water permeable sheets 1, and the adhesive 3 is distributed fibrously between layers of the inorganic particles 2 to form a water impervious sheet. The hot-melt adhesive 3 is sprayed like a spider's net on the permeable polyester non woven fabric 1 having a tensile strength at about 30kg/5cm width, and thereafter, bentonite granulated products, which has a particle diameter of about 1.5mm and a length of about 2.5mm and shows the elasticity at an ordinary temperature, are stuck immediately at a predetermined thickness. This process is repeated sometimes to laminate the permeable polyester non woven fabric, and they are rolled by a pressurizing roller to form a water impervious sheet having a thickness of about 15mm. A permanent water impervious sheet having high reliability and any desired thickness is thereby obtained.