Continuous venting of a covering sheet for an in-situ lamination process

A method of venting a rear facer sheet for lamination is accomplished by continuously drawing the rear facer sheet through a perforating device which creates conical apertures in the rear facer. Two metal rails affixed to opposing edges of a front facer are continuously drawn into a laminator after first having an expanding foam material continuously deposited onto the upper surface of the front facer. The perforated rear facer is continuously drawn into the laminator and affixed to the two metal rails, creating an enclosed volume in which the expanding foam is located. The apertures in the rear facer allow for the escape of gasses and air during lamination, promoting even flow and uniform density of the foam material. The perforating device has an upper and a lower rotating cylinder, the lower cylinder being equipped with piercing elements and the upper cylinder being equipped with grooves corresponding to the piercing elements.