Patent ID: 8876014

Claim:
A method comprising providing a polyurethane-filled ballast layer spraying a first reaction system onto a surface of the polyurethane-filled ballast layer to form a polyurethane external protective layer, wherein the first reaction system comprises 1a) one or more polyisocyanates having a general formula R(NCO) n , wherein, R is selected from the group consisting of an aliphatic alkyl group comprising 2 to 18 carbon atoms, an aromatic alkyl group comprising 6 to 15 carbon atoms and an arylated alkyl group comprising 8-15 carbon atoms, and n is an integer from 2 to 4; 1b) one or more polyether polyols and/or amine terminated polyether, having an average molecular weight of more than 200 and a functionality from 2 to 6; 1c) one or more extender; and 1d) from 0 to 0.5% by weight of one or more blowing agent, based on 100% by weight of 1b) and 1c); wherein the tensile strength of the polyurethane external protective layer is from 4 to 20 MPa.