PURPOSE: To simplify a water-proofing treatment work for a reinforced concrete wall by using a water-proof formwork previously coated with a water-proofing agent as an outside formwork for concreting.

CONSTITUTION: A water-proof formwork 7 is made up by integrally combining a concrete plate 9 with a water-proofing material 8 whose one side is coated with asphalt, iron bars 12 for the formwork having projected iron bars 11 in its netting portion 10, and a concrete plate 13 through which the iron bars 11 are projected. When constructing a water-proof concrete wall, main iron bars 3 are first set on a mat 1, a wood formwork 4 is set in the inside of the main iron bars 3, and then a water-proofing formwork 7 is set on the outisde of the formwork 4. At the time, the projected iron bars 11 are crossed with the main iron bars 3, the water-proofing material 8 is turned outwards, and then the joints of the water-proofing material 8 of the adjacent water-proof formworks 7 are hot bonded by heating. Afterwards, concrete is placed into the space between both the formworks 4 and 7.