Construction

Common Materials Common driveway and walkway materials include concrete, asphalt (blacktop), soil, gravel, flagstone, and pavers made from masonry units (bricks) or concrete. Common patio materials include concrete, flagstone, and pavers. Concrete patios are sometimes covered with tile or other finish materials such as outdoor carpet. Concrete can be stamped and colored to provide the appearance of flagstone and pavers. Carpet is sometimes used to conceal cracked concrete.

Walkways are occasionally made using pressure treated wood or railroad ties. These materials are common when a walkway consists of different levels on a steep lot where the walkway forms a long stairway. Pressure treated wood smaller than 4×4 inches may not be rated for ground contact. Walkways made from wood can deteriorate in wet climates and may reach the end of their service life rapidly.

Construction Techniques Driveways, walkways, and patios rely on the soil and the base materials underneath to provide support and to resist settlement, uplift, and cracking. Preparation of this subbase is important for avoiding problems, and lack of proper subbase preparation is a common reason for problems. Driveways, walkways, and patios should be placed on compacted, dry soil which has had the top soil and vegetation removed.

Concrete driveways, walkways, and patios should be at least 3½ inches thick. Crack control joints should be installed in these structures at about 10 foot intervals and at depth of about ¼ of the slab thickness. Crack control joints are grooves installed soon after the concrete is poured. They allow the concrete to crack at the joint instead of cracking randomly in the slab. Cracks in control joints are normal and are not usually a deficiency unless the cracks are very wide or there is vertical displacement. Isolation joints should be installed where the driveway and walkway meet and where the driveway or where the walkway meets other structures such as the house or a column. Isolation joints are often made from asphalt impregnated fiberboard. Isolation joints reduce cracking by allowing the concrete and adjacent materials to move at a different rate.

Many concrete defects can be traced to improper placing, finishing, and curing. Concrete should not be placed when the temperature will fall below 32° F. within 24 hours. Spalling (popping of the surface layer) is a common result of concrete that freezes before it cures. Improper finishing techniques can cause problems such as dusting (powdery material on the concrete’s surface). Crazing (numerous small surface cracks) can be caused by concrete that dries too quickly (in hot weather) and by concrete that has too much water in the mix.

Asphalt (blacktop) driveways and walkways should be between at least 2 and 4 inches compacted (installed) thickness. Crack control and isolation joints are not necessary for asphalt driveways and walkways.

Many asphalt defects can be traced to improper use and maintenance. Asphalt softens when the temperature rises, so heavy vehicles and even cars can leave tire tracks. Turning wheels while the vehicle is stationary can be especially damaging. Asphalt cracks are inevitable and can be made worse in areas with freeze/thaw cycles. Regular sealing of asphalt is a necessary maintenance procedure to help reduce expansion of common cracks. Gasoline and especially diesel fuel can disintegrate asphalt.

Proper subbase preparation is essential for the long-term performance of driveways, walkways, and patios made from flagstone and pavers. Improperly installed flagstone and pavers are likely to shift and settle creating a trip hazard and places where water can accumulate. A subbase consisting of compacted gravel (a crusher run) and compacted sand is usually specified by manufacturers. Special polymeric sand may be used to fill the spaces between the flagstone and pavers in a manner similar to grout between ceramic tiles.

Driveways, walkways, and patios should slope away from the house and should not impede water flow. They should not be placed above the foundation level at or above the framing level. Hard surfaces such as these should slope away from the house at least ¼ inch per foot. It is common to install walkways several feet from the house, in which case a foundation planting area is often created between the house and the walkway. The walkway should be installed so that water flows over the walkway and is not trapped behind it. An alternative to water flowing over the walkway is installing a catch basin and a pipe running under the walkway.