Patent ID: 8894901

Claim:
A method of making a sheet of building material for roofing or siding applications, comprising the steps of: (a) preparing a mixture comprising a thermoplastic resin and a mineral filler, said resin comprising about 10% to 40% by weight of said mixture and said filler comprising about 60% to 90% by weight of said mixture, said resin comprising one of polyethylene and polypropylene; (b) mixing said mixture at a temperature above the melting range of said resin; (c) forming said mixture into a sheet, said forming step being done at a temperature above the melting range of said resin; (d) allowing a surface of said sheet to cool to a temperature below the midpoint of the melting range of said resin, said temperature being in the range of 210 to 220 degrees F. when said resin comprises polyethylene and in the range of 220 to 250 degrees F. when said resin comprises polypropylene; and (e) straining said sheet by calendering, rolling or pressing said sheet when said surface temperature is within said temperature range of step (d) to increase a length of said sheet by 1% to 10%.