Modified stone plays a number of essential roles in construction. The closest most homeowners come to describing modified stone is the general term "gravel." In fact, gravel is what modified stone is not. A critical component of drainage beds to support buildings, barns and sheds, modified stone also provides the foundation and finish layers of unpaved roads, driveways and landing pads.
Modified Stone is Not Gravel
Real gravel occurs in nature and is composed of small stones, often burnished round by the action of water. Stones are commercially sorted and can be purchased in several sizes, from the small pea gravel in the bottom of your fish tank to the more substantial stones added to cement and sand to form concrete.
Modified stone, on the other hand, begins as big rocks and boulders. Rocks are mechanically crushed and marketed in a number of sizes, numbered from small to large. Pieces range in size from quarter-sized to nearly coarse sand, called "fines." The size most in demand for residential use is 2, often 2A.
Crushed rocks are not rounded or smoothed. Their sharp edges help them cling to each other and the area in which they are placed. Mechanical compression can be applied to increase the stone's adherence. Modified stone is usually sold in tons; a ton constitutes approximately 1 cubic yard of stone.
Aggregate rock, river rock and shale are among several modified stone products available for residential use. Some suppliers offer reddish-toned, bluish or dark-toned mixtures as well. Most stone is medium gray in appearance. Crushed white quartz and marble are marketed in small quantities as flower-bed edging.
Builders use modified stone to create a level surface and drainage bed for barns, sheds and other utility buildings erected without foundations. Stone also provides a firm foundation for patios paved with brick or cement blocks. For parking areas, landing pads, walkways and driveways, number 2A stone predominates. So-called "gravel roads" employ a broader range of sized modified stones, with fines used as a finishing coat.