How long before you can drive on new concrete?

Concrete cures, it does not dry

Concrete gets hard through a chemical reaction between cement and water, so it's not just drying out. That reaction goes on for weeks, and it needs moisture and warmth. If a slab dries too fast, the top never reaches full strength, and it can dust or scale for the rest of its life. That's why a surface can look done and still be far from ready.

Concrete reaches about 70 percent of its design strength in 7 days, and reaches its design strength at about 28 days. It keeps on gaining slowly after that. The 7-day mark for cars comes from that first number. It's enough for ordinary use, as long as you avoid turning your wheels while you're parked, which grinds the fresh surface.

The first week, day by day

Here's what normally happens after a driveway is poured in decent weather.

• Pour day: keep people, pets and leaves off the surface
• Within about a day: saw cuts go in before random cracks can form
• Days 1 to 2: light foot traffic is fine, and forms start coming off
• Days 2 to 3: backfill along the edges, once the concrete is strong enough
• Days 1 to 7: keep it curing with a curing compound, a cover or a light mist
• Day 7: cars may use it, and try to avoid sharp turns on the slab
• Day 28: open it to heavy loads, and think about sealing it

Can you pour a driveway in winter?

You can, but it takes more care and more money. The main rule is that fresh concrete must not freeze. If it freezes in the first day or so, it can lose a big share of its strength for good. Below about 40 degrees, the work counts as cold-weather concreting. The crew may use warm mix water, an accelerator and insulated blankets, and it needs to keep the slab above 50 degrees for the first few days.

The ground must not be frozen either, since frozen ground can settle when it thaws and it chills the slab from below. In a normal Pittsburgh year, you can often pour from April through early November, with more risk at both ends. If you can wait until spring, you'll usually pay less and get a slab with a better first winter ahead of it, because new concrete shouldn't be salted in its first season.

What about rain or heat?

Light rain after the surface has been finished usually does no harm. Rain during finishing is another matter. Water worked into the top weakens it, which can lead to dusting and scaling later on, so crews cover the slab or wait. A heavy storm on a fresh slab can pit the surface. We watch the forecast and move the pour when we need to.

Hot, dry and windy days are their own problem. The top can dry and crack before the crew is finished. Starting early, dampening the base and using a curing compound right after finishing all help. A driveway poured in the shade of a house may also set at a different rate from one in full sun, so the crew has to keep an eye on that.

Caring for a new driveway

The first year has an outsized effect on how a slab ages. A few simple habits make a real difference.

• Keep cars off for at least 7 days, and heavy trucks for 28
• Don't use deicing salts in the first winter
• Use sand for traction instead
• Clear snow with a plastic shovel where you can
• Clean up oil, gas and fertilizer soon after a spill
• Don't let cars sit with hot tires on fresh concrete

What crews do to help a slab cure

Good curing is mostly about keeping moisture in. Most crews spray a curing compound right after finishing, which forms a thin film that slows drying. Others cover the slab with plastic or wet burlap. On a cool day, insulated blankets hold in the heat the concrete makes as it hardens. If your quote doesn't say how the slab will be cured, ask, since it's cheap to do and costly to skip.

After the cure

Once the slab has cured for a month and the weather is right, a penetrating sealer is your next step. See concrete driveway sealing for when and what to use. If you're planning a pour and want a price, the concrete driveway cost estimator gives you a planning range for your size and finish.

Common questions

More driveway services

• concrete driveway installation
• concrete driveway replacement
• concrete driveway repair
• concrete driveway resurfacing
• stamped concrete driveway
• exposed aggregate concrete driveway
• driveway trench drain
• driveway drainage
• driveway apron
• concrete driveway sealing
• driveway crack repair
• sunken driveway repair
• driveway extension

Areas we serve

• Lawrenceville
• Shadyside
• Squirrel Hill
• Bloomfield
• Wexford
• Sewickley
• Fox Chapel
• Allegheny County