the method of the present invention involves taking a comminuted mixture of waste plastic materials , feeding the mixture into a screw extruder capable of applying heat and pressure to the mixture ; using the screw extruder to heat the mixture to a temperature of between 350 ° and 600 ° fahrenheit ; and forcing the molten mixture outwardly through a die opening under a pressure of from 100 lbs . per sq . inch to 600 lbs . per sq . inch into a mold in tightly sealed relationship over the die opening . the mold , after being filled , is removed from the screw extruder , and the mixture is permitted to cool and harden in the mold . the hardened mixture is then removed from the mold .