The timeline
| Time after the pour | What is safe |
|---|---|
| 24 to 48 hours | Walking on it. Keep pets, bikes and anything with a kickstand off the surface. |
| 7 days | Cars and light pickups. Drive straight on and off, and avoid turning the wheels while stopped. |
| 28 days | Heavy vehicles: loaded trucks, trailers, RVs, a dumpster or a moving van. This is when concrete reaches its design strength. |
These are typical figures for mild weather. In cool spring or fall weather concrete gains strength more slowly, so follow what your contractor tells you for your pour.
Curing: the first week
Concrete gets stronger for as long as it holds moisture, and a slab that dries out too fast ends up with a weak, dusty surface. Most contractors spray on a curing compound as soon as the finishing is done, and it does the job by itself. If yours asks you to keep the slab damp with a sprinkler for a few days, do it. Keep the edges supported, too: do not drive off the side of new concrete or dig along it.
Sealing
A penetrating sealer soaks into the surface and keeps water and salt from getting in. For a Michigan driveway it is cheap insurance.
- When: after the concrete has cured, usually about 28 days, and before the first winter. Some curing compounds also act as a first-season sealer, so ask what was used.
- What kind: a penetrating sealer (silane or siloxane) for driveways and walks. It does not change the look or make the surface slippery.
- How often: every few years. If water stops beading on the surface, it is time.
The first winter
New concrete still holds extra water in its first winter, which is exactly when salt does the most damage.
- No deicing salt in the first winter. Use plain sand for traction.
- Never use fertilizer as a deicer. Products containing ammonium nitrate or ammonium sulfate attack concrete chemically, at any age.
- Mind what the car brings home. Road slush packed in the wheel wells is full of salt, and it melts onto the garage apron. Knock it off at the street when you can, and rinse the apron on days above freezing.
- Shovel early and use a plastic blade. Clearing snow before it packs down means you never need a deicer, and plastic will not chip the surface.
After the first winter, a sealed, air-entrained driveway can cope with ordinary rock salt used sparingly. Sand is still kinder.
What is normal and what is not
- Normal: hairline cracks, especially along the control joints. Blotchy color for the first few months. A white powdery film that washes away.
- Call the contractor: the surface flaking or peeling in sheets, cracks you could fit a coin into, a crack with one side higher than the other, or water pooling against the house.
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