Crushed Fines, or Quarry Dust, is a form of fractured gravel chips and fine dust used in the construction of patios and walkways whose topmost layer consists of mortarless (or "dry-laid") pavers. The first layer in the construction of such a surface is called the subgrade-- this is the layer of native material underneath the intended surface. It is usually compacted and stabilized. Next comes the base course (also called the aggregate base course or ABC) composed of crushed rock and gravel varying from 1 inch down to dust-particle size. It too is typically compacted and evened. The next layer will be the crushed fines, composed of course crushed chips and quarry dust. Next the Paver Base Sand typically laid between 1 inch and 2 inches thick, depending on anticipated traffic. The pavers are then laid on top of this, and then a uniform, fine-grained polymeric sand is poured between them.