PURPOSE: To increase the strength of placed concrete and to ensure excellent appearance of a finish surface by a method wherein a sheetform substance consisting of an ethylene copolymer is heated and adhered on the surface of a foundation bed having a number of through-holes to form forms.

CONSTITUTION: A filmform adhesive 4 of an acid denatured ethylene-vinyl acetate copolymer is superposed on a foundation bed 3. After the lamination is preheated to the melting point of the film 4 up to 140°C, it is contact-bonded by a press. In this case, an ethylene copolymer of an acid denatured ethylene- vinyl acetate copolymer is a substance in which unsaturated carbon acid or an anhydride content is 0.01 - 30 wt.% and which has a melt point of 60 - 120°C. A porous sheet 5 having a number of holes is superposed thereon, the lamination is heated to the melt point of the film 4 - 140°C, and pressed again for contact- bonding to form a sheathing board 2. Reinforcing ribs 7 and 8 are arranged on the back of the sheathing board 2 to form forms 1, and concrete is placed by using the forms 1. This constitution causes the porous sheet 5 to discharge surplus moisture content and air bubbles in the concrete to the outside to increase strength, and enables ensurance of excellent appearance of a finish surface.