A driveway starts with the base
Most driveway failures start below the concrete. A slab poured on soft, poorly compacted or saturated soil will crack and settle no matter how good the concrete is. A durable driveway begins with:
- Excavation to remove topsoil, roots and organic material.
- A compacted subgrade that's firm and evenly supported.
- A compacted aggregate base, typically crushed rock, which provides a stable, well-draining layer.
- Grading so the finished driveway drains water away from the house and doesn't send it onto neighbors' property.
Ask the contractor how deep they'll excavate, what base material they'll use, how thick it will be, and how they'll compact it.
Thickness and reinforcement
Residential driveways are thicker than walkways because they carry vehicles. Areas that will carry heavier loads, such as RVs, boats or delivery trucks, need more thickness. Reinforcement, such as steel rebar or welded wire mesh placed correctly within the slab, or fiber reinforcement in the mix, helps control cracking and hold cracked sections together. Reinforcement only helps if it's positioned in the slab, not lying on the ground beneath it. Ask what thickness and reinforcement the contractor recommends for how you'll use the driveway.
Joints
Concrete shrinks as it cures and moves with temperature, so it cracks. Control joints, which are cut or tooled grooves, give the cracks a planned, straight place to form. Joint spacing depends on slab thickness. Isolation joints separate the driveway from the garage slab, the house, the sidewalk and other fixed objects so they can move independently. Ask to see the joint layout.
The concrete mix
A contractor should order a mix suited to driveways and to the local climate. In cold climates with freeze-thaw cycles, air-entrained concrete, which contains tiny air bubbles that give water room to expand when it freezes, is important for durability. The water content matters too: adding extra water at the site to make concrete easier to work weakens it.
Finishing and curing
A broom finish provides traction. After finishing, concrete needs to cure: it must keep enough moisture and stay within a reasonable temperature range for days while it gains strength. Curing compounds, wet curing or covers help. Pouring in extreme heat or cold requires extra precautions. Ask how the contractor will cure the slab and how long before you can walk and drive on it.
Repair or replace?
Small cracks can be sealed to keep water out. Sunken sections can sometimes be lifted by slab jacking or foam injection. Widespread cracking, crumbling surfaces, large settled areas or a driveway that drains toward the house usually call for replacement.
The approach and permits
The section of driveway between the street and the sidewalk or property line, often called the approach or apron, is frequently in the public right-of-way. Replacing it typically requires a permit from the city or county, and it may have to meet specific standards. Ask the contractor who handles the permit.
Questions to ask
- How deep will you excavate, and what base will you install?
- What thickness and reinforcement will you use?
- Where will the joints go?
- What concrete mix will you order, and will it be air-entrained?
- How will you cure the slab, and when can I drive on it?
- Is a permit required for the approach, and is it included?
Edges and borders
Driveway edges crack and crumble when soil washes out from under them. Backfill and grade along the edges after the forms come off, so the slab is supported to its edge.