Prefabricated modified composite polymer-bitumen waterproofing membrane composed of distilled bitumen and differentiated waterproofing masses, specifically designed for use over old bituminous waterproofing membranes self-protected with mineral slates. The upper face compound is composed of distilled bitumen and elasto-plastomers while the lower face compound is composed of distilled bitumen and special polymers which provide particular characteristics of adhesion & workability. A special waterproofing mass is used to bond the upper & lower compounds.