Why concrete needs time
Concrete doesn't harden by drying out. It hardens through a chemical reaction between cement and water called hydration, which keeps going for weeks as long as there's moisture in the slab. That's why the grade on your quote, N20, N25 or N32, is the strength in megapascals the concrete must reach at 28 days, not on the day it's poured.
Most of the strength comes early. In mild weather a typical residential mix reaches roughly two thirds of its 28-day strength in the first week, which is plenty for a family car and not enough for a loaded truck.
A timeline for the first month
| Time after the pour | What's OK |
|---|---|
| First 24 hours | Nothing. Keep people, pets and hoses off. Sawn joints usually go in during this window. |
| 1 to 3 days | Careful foot traffic. Formwork usually comes off. The slab should still be curing under a compound or cover. |
| 7 days | Cars and small utes, driving in and out in a straight line. |
| 28 days | Heavier vehicles: delivery trucks, removalists, caravans, boats and skip bins. Many film-forming sealers go on around now. |
Curing matters as much as waiting
Waiting only helps if the concrete keeps its moisture. If the surface dries out in the first few days, the top few millimetres never reach full strength, and the driveway wears, dusts and scales sooner. CCAA recommends curing residential driveways and paths for at least 3 days, and 7 days within a kilometre of the coast or where traffic is heavier.
Curing means a sprayed curing compound, plastic sheeting, or keeping the slab continuously wet. Hosing it once in the morning and once in the afternoon doesn't count: CCAA notes that wetting at intervals doesn't keep concrete continuously moist and can harm the surface in hot weather. Coloured concrete is normally cured with a compatible compound or sealer, because plastic and wet hessian can leave blotchy patches.
Weather changes the timeline
Cement reacts faster in warmth and slower in cold. A slab poured in a Sydney summer gains strength quickly but also loses moisture quickly, so curing is the bigger risk. A winter pour in Penrith or Campbelltown, where mornings can get close to freezing, hardens more slowly, so it's sensible to wait an extra couple of days before the first car. More on this in pouring concrete in heat and rain.
What damages new concrete in the first month
- Heavy point loads: car jacks, trailer jockey wheels, skip bin feet and ladders on unprotected edges.
- Turning a stationary car's steering wheel, which grinds the young surface.
- Driving over the slab edges before the ground beside them has been backfilled and compacted.
- Fuel, oil or fertiliser spills, which stain fresh concrete deeply.
- Pressure washing at close range before the surface has properly hardened.
Planning the week after your pour
Most people underestimate how inconvenient a week without the driveway is. Before pour day:
- Work out where you'll park. Street parking is tight in many inner suburbs, so talk to neighbours early.
- Get bins, bikes and anything you'll need out of the garage.
- Rebook deliveries and ask couriers not to drive in. Put tape or a barrier across the entry.
- Push back anything that needs a truck on the driveway, such as a skip bin, a landscaping delivery or a removalist, until four weeks after the pour.
- Ask how the slab will be cured and whether you need to do anything, like keeping covers in place.
Our pour day guide covers getting the property ready for the concrete truck.
Planning a concrete job?
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Common questions
Can I walk on concrete after 12 hours?
Usually, for a few careful steps, if the weather has been mild. The surface is still soft enough to mark and the edges can chip, so wait the full 24 hours unless you have to cross it.
What if it rains the day after the pour?
Rain on concrete that has already set is generally fine and even helps it cure. The damage happens when heavy rain hits the surface in the first few hours, before it has been finished and stiffened.
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Sources
Prices in this guide come from our concrete price calculator and update when its rates are reviewed. They are estimates, not fixed quotes: the final price is confirmed at a free site inspection. Council rules were checked against each council's published policy and can change, so confirm with your council before you build.
