The two-layer system
A proper tarmac driveway is laid in two distinct layers. The binder course (sometimes called the base course) is 65mm of 20mm aggregate hot-mixed with bitumen, the structural body of the driveway. The wearing course is 25mm of 6mm aggregate hot-laid on top, the smooth, fine-textured surface you actually see. Operators who skip the binder course and lay only a thin wearing course are saving themselves a day and you a decade of life.

