Ask your Licensed Concrete Contractor

Find out how thick your driveway should be, what the proper rebar spacing is and more.

Updated February23,2023

South Pacific Concrete in Kailua Kona, HI

To ensure that your concrete driveway will look good for many years to come, there are important specifications your contractor should follow during installation. How well your driveway looks and performs long-term is largely related to the quality of workmanship and materials that go into it. To help ensure a problem-free driveway, use the following list for information about proper concrete construction.

Placing concrete to proper thickness

Thickness is the major factor (even more than the strength of the concrete) in determining a driveway’s structural capacity. Place concrete at a minimum thickness of 4 1/2 to 5 inches. At a the thickness of 4 1/2 to 5 inches the stress of daily traffic, deliveries or use of service trucks will not damage your driveway.

Also consider thickening the edges of the driveway by 1 or 2 inches to provide additional structural support in the area most likely to be subject to heavy loading. The thickened sections should extend in from the slab edge 4 to 8 inches.

Your local soil conditions and weather patterns may also require a thicker driveway slab. Contact a local driveway contractor for an expert recommendation.

Rebar & wire mesh reinforcement

Using steel reinforcement will provide additional structural capacity for your driveway and is especially important if the slab will be exposed to heavy traffic. Reinforcement won’t prevent cracks, but it will help hold them together if they do occur.

Concrete reinforcement can be either 6×6 wire mesh or 3/8-inch to #4 steel rebar. Use wire mesh for driveways that are 4 to 5 inches thick, and rebar for those that are 5 inches or more. Place rebar in a grid pattern with a spacing between bars of approximately 18 inches. In either case, blocks should be used under the reinforcement to lift the reinforcement and keep it centered within the concrete.

Synthetic fibers have also proven to be beneficial in driveways as a way to reduce shrinkage cracks. Fibers will not provide structural reinforcement, however. Adding fibers to concrete helps to reduce stress cracking in the concrete, but the fibers are no replacement for steel-reinforcement as they do not aid in flexural strength, or the ability for concrete to bend without breaking. Also if cracked the Fibers will Not hold the concrete from separating as Rebars or Mesh would.

Soil composition and compaction

Uniformity, in both soil composition and compaction, is the key to a good sub-grade, one that will provide adequate support, ensure an even slab thickness, and prevent slab settlement and structural cracking. Soft spots should be removed and replaced with good material, such as gravel or crushed rock. Many western states have expansive soils. In these conditions, 2 to 8 inches of crushed rock should be used as sub-grade material, depending on the degree of expansiveness. If you are unsure about the soil characteristics in your area, consult a soils engineer.

Don’t allow the concrete to be placed on bone dry sub-grade, spraying the sub-grade first to dampen it will prevent it from wicking water from the fresh concrete and producing spider cracking due to quick loss of moisture.

Vibratory plate compactors and rollers are the most common machines used for sub-grade compaction of residential driveways. Click here to read more about concrete slabs.

Readymix Concrete

Mix design from the ready-mix vendor will also impact the performance and longevity of a concrete driveway. Ask your Licensed Concrete Contractor more about concrete driveway mix design to find out exactly what to ask for and the Mix design being used for your home or Business Project.

Placing Control Joints and Decorative Cuts

To help random cracking, control joints should be placed at a minimum spacing of 10 feet for a concrete driveway. Concrete will crack as it drys so Control Joints are placed to help the concrete to crack at predetermined areas in to be structurally sound and decoratively appealing. The depth of control joints is also critical. Your concrete installer should hand tool or saw-cut them to a depth equaling one-fourth the slab thickness (or 1 inch for a 4-inch slab). Driveway control joints can be incorporated into a decorative pattern, with a crack chaser to open up the cut adding to the decor.

In addition to control joints, a construction joint should be installed where the driveway meets a sidewalk, garage floor slab, and other existing pavements. Ask your contractor to provide a jointing plan as part of his written proposal.

Proper finishing

Finishing is generally a four-step process:

• Placing and Striking Off the concrete with a screed to achieve a uniform surface.
• Floating the concrete with a wood or magnesium bull-float before bleed-water accumulates to help consolidate and knock large aggregate down so the concrete paste will be available for finishing at the top of the slab or driveway.
• Sealing with steel trowels and fresnos if to be hard trowel finished or to achieve a finer finish with other decorative dextures being placed.
• Applying a simple broom finish to improve traction, stamping the driveway or applying another type of decorative textured finishes (see Making Concrete Slip Resistant).

Proper drainage

To eliminate standing water on your driveway, it should be sloped toward the street and away from existing structures (such as your house and garage) a minimum of 1/8 inch per foot, recommends the Portland Cement Association. If proper drainage cannot be achieved because the concrete slab is between two structures, you may need to install an area drain that will collect the water at a low point in the concrete and divert it away to existing drain facilities or a lower area on your property.

Concrete curing techniques

Allowing the concrete to cure undisturbed after is completed is key in caring for your newly place slab or driveway. Curing of the concrete is the final step of the process, and one of the most important. Unfortunately, it’s also one of the most neglected. In extreme cases, failure to allow the concrete to cure completely can result in strength reductions of up to 50% by reducing the concrete’s resistance to the effects of weather and increasing the possibility of surface defects and ruining a decorative finish.

Depending on the type of weather in your location, curing may include covering the concrete with plastic sheets or wet curing blankets, continuous spraying, moistening, or an application of a liquid membrane-forming curing compound. For slabs that are to be acid stained, wet curing is the best approach, since a curing compound would have to be completely removed to allow the acid stain to penetrate. The most common way to cure plain or integrally colored concrete, though, is to use a liquid curing compound.

Tip: Let your concrete cure for at least three days before driving on it. Learn more in How Long Before You Can Drive on New concrete?