A driveway expansion joint, also known as an isolation joint, is a space put between adjoining sections of concrete to help control cracking. An expansion joint may also be placed between a driveway and adjacent concrete slabs, such as the foundation of a house or garage. These planned spaces allow each section of concrete to move independently of the others. Concrete expands in hot weather and contracts in cold and, without expansion joints to provide room for this movement, large cracks could occur. Poured concrete driveways are the only driveways that need expansion joints.
The number of expansion joints necessary in a driveway depends on its length. Shorter driveways, such as those frequently seen in newer housing developments, may have only two joints. Typically, there is one between the driveway and the slab of the garage or carport, and another between the driveway and the sidewalk or street it abuts. A driveway expansion joint should be placed every 30 feet to 60 feet (9.1 m to 18.3 m) on a longer drive.
A driveway expansion joint, as a rule, is from 1/2-inch to 3/4-inch (12.7 mm to 19 mm) wide and as deep as the concrete slab is thick. Preformed materials, such as asphalt fiberboard, rubber, and plastic or cork composition planks, are common joint fillers. Any material used as filler for a driveway expansion joint must be extremely resilient and not subject to becoming soft in hot weather or brittle in cold. After being installed in the expansion spaces, these materials themselves are referred to as the joints.
Expansion joints in the driveways of older homes are often filled with weeds as the result of a wooden driveway expansion joint used by building contractors in years past. When the wood rots, all that remains is a crack as wide as the board that originally filled it. The space quickly fills with dirt, rocks and weeds and becomes an eyesore. The problem can be solved by cleaning out the joints and installing proper material in them. If gaps are wider than the purchased filler, expandable, weatherproof caulk can be used to fill in the excess space.
When building a driveway, it is prudent to consider other types of joints that may help prevent cracks. Driveways need transverse control joints every 12 feet to 20 feet (3.65 m to 6 m) of their length. Longitudinal control joints are necessary for every 12 feet (3.65 m) of width, which results in the attractive grid pattern seen on wide driveways and those with turning aprons or parking courts. A control joint differs from a driveway expansion joint in that it extends to only 1/4th the depth of the slab and is usually only 1/4-inch to 1/2-inch (6.35 mm to 12.7 mm) wide. An architect or experienced contractor can provide expert information on the various types of concrete joints and advice on when and how to use them.