Brushed Concrete Driveway 101: All the Basics You Need to Know

There are important specifications that your contractor should follow during installation to ensure that your concrete driveway will look good for many years to come. The quality of workmanship and materials used in the construction of your driveway will have a large impact on how well it looks and performs in the long run. Use the following list of information about proper driveway construction to help ensure a problem-free driveway.

CONCRETE DRIVEWAY THICKNESS & CONSTRUCTION BASICS

• Placing concrete at the proper thickness

Thickness is the most important factor in determining a driveway’s structural capacity (even more than concrete strength). Pour concrete to a thickness of at least 4 inches. According to the Tennessee Concrete Association, increasing the thickness of your concrete from 4 inches to 5 inches will add approximately 20% to the cost of your concrete but will increase the load-carrying capacity of your driveway by nearly 50%.

Consider thickening the driveway edges by 1 or 2 inches to provide additional structural support in areas that are likely to be subjected to heavy loading. The thickened sections should extend 4 to 8 inches from the slab edge.

Local soil conditions and weather patterns may necessitate a thicker driveway slab as well. For an expert recommendation, contact a local driveway contractor.

• Rebar & wire mesh reinforcement

Steel reinforcement will add structural capacity to your driveway, which is especially important if the slab will be subjected to heavy traffic. Reinforcement will not prevent cracks, but it will assist in keeping them together if they do occur.

Wire mesh or 12-inch (#4) steel rebar can be used for reinforcement. For driveways, 4 to 5 inches thick, use wire mesh, and for driveways 5 inches or thicker, use rebar. Place rebar in a grid pattern with approximately 12-inch spacing between bars. Blocks should be used under the reinforcement, in either case, to keep it centered within the concrete.

Synthetic fibers have also been shown to be useful in reducing shrinkage cracks in driveways. Fibers, on the other hand, will not provide structural reinforcement.

• A properly prepared subgrade

The key to a good subgrade is uniformity in both soil composition and compaction—one that will provide adequate support, ensure an even slab thickness, and prevent slab settlement and structural cracking. Soft spots should be filled with good material, such as gravel or crushed rock. Soils are abundant in many western states. Depending on the degree of expansiveness, 2 to 8 inches of crushed rock should be used as subgrade material in these conditions. Consult a soils engineer if you are unsure about the soil characteristics in your area.

Don’t allow the concrete to be placed on a bone-dry subgrade. Spraying the subgrade first to dampen it will prevent it from wicking water from the fresh concrete.

• The correct concrete mix

A concrete driveway’s performance and longevity are influenced by the mix design. Learn more about concrete driveway mix design to determine exactly what to request.

• Correctly placed joints

Control joints should be spaced at a maximum of 10 feet apart for a 4-inch-thick driveway slab to help prevent random cracking. While random cracks are not a structural issue and will not shorten the life of the driveway, they can be an eyesore. Avoid joint patterns that result in rectangular or triangular sections as well. The depth of the control joints is also important. Hand tool or saw cut them to a depth equal to one-fourth the slab thickness by your concrete installer (or 1 inch for a 4-inch slab).

Aside from control joints, an isolation joint should be installed where the driveway meets a sidewalk, garage floor slab, or other existing pavements. Request that your contractor include a jointing plan in his written proposal.

• Proper finishing

Overworking the surface and performing finishing operations while bleed water is present are the two most common mistakes made when finishing concrete driveways.

Finishing is usually done in three steps. Your contractor must:

• Level or strike off the concrete with a screed to achieve a uniform surface.
• Float the concrete with a wood or magnesium bull float before bleed water accumulates.
• Apply a simple broom finish to improve traction-unless plans call for stamping the driveway or applying another type of decorative textured finish 

Final finishing with a steel trowel is unnecessary and can actually cause more harm than good by prematurely sealing the concrete surface and preventing bleed water evaporation.