How long before I can walk or drive on new concrete?
Set, cured and fully strong are three different things at three different times — and what each one lets you do without damaging the slab.
- Difficulty
- beginner
- Time
- 8 min
- Read
- 3 min
Short answer
Foot traffic is usually fine after a day or two in normal weather, once the surface will not mark. Vehicles and heavy loads need considerably longer, and concrete is conventionally assessed at 28 days, by which time it has most of its strength. It keeps gaining strength slowly for months. Cold weather stretches all of these substantially.
The question is really three questions. When will it stop taking a footprint? When is it strong enough to be used? And when has it finished gaining strength? Those have different answers, and the reason no honest guide gives you exact hours is that temperature changes them enormously — the same mix that is walkable in a day in June may not be in December.
Step by step
- Distinguish setting from curing.Setting is the concrete going from plastic to solid, in hours. Curing is the long chemical reaction that develops strength, over days and weeks. A slab that is set is not a slab that is strong.
- Keep off entirely while it is finishing.Until the surface has been floated and has stiffened, anything on it leaves a permanent mark. Rope it off and keep children, cats, foxes and delivery drivers away — animal prints in a new drive are a rite of passage nobody enjoys.
- Wait for foot traffic until it will not mark.In normal mild weather this is commonly a day or two. Test at the edge with a thumb rather than walking out into the middle to find out.
- Give it far longer before anything heavy.Vehicles, skips, scaffolding, a loaded barrow or stacked materials impose loads a young slab cannot take. The concrete is nowhere near full strength in the first week, and loading it early causes cracking that appears later.
- Use 28 days as the reference point.Concrete strength is specified and tested at 28 days, and by then it has the great majority of the strength it will ever have. It is the conventional point at which a slab is treated as being at its design strength.
- Add substantially for cold weather.The reaction slows dramatically as temperature falls, and near freezing it very nearly stops. A slab poured in a cold snap can take several times as long to reach the same strength, and the delay applies to every stage.
- Keep curing it during the wait.The first week matters most. Keep it damp and covered rather than letting it dry — this is the period where curing makes the difference between the strength you specified and something considerably less.
- Leave the formwork on as long as you can.It protects the arrises and retains moisture. Strip when the edges will not break away, and take the fixings out rather than levering the boards off.
- Delay anything you build on it.Bolting down a shed, building a wall or fixing anything into the slab needs the concrete to be able to take a fixing without blowing out. Give it well beyond the walking-on point.
Tips
- Water is not the enemy while it cures — the opposite. Rain on a set slab is fine and mildly helpful. It is rain on a fresh, unset surface that causes damage.
- Frost within the first days is the one genuinely destructive event. Insulate rather than just cover if a frost is coming.
- If you need to work on a fresh slab, spread the load with boards rather than walking on it directly.
Questions people ask
Can I drive on a new drive after a week?
It is very early. The slab is well short of its design strength, and early loading causes cracks that show up months later. Ask the supplier or specifier what they recommend for the mix used — several weeks is not an unusual answer for vehicle loading.
Why 28 days?
It is the standard age at which concrete strength is specified and tested. It is not the point at which curing stops — concrete keeps gaining strength for months and years — but it is the reference figure everything is quoted against.
Does covering it make it take longer?
No. Covering keeps it damp, which is what makes it gain strength faster and further. A slab left to dry out early is both weaker and no quicker.
It rained the day after I poured. Is it ruined?
If the surface had already stiffened and been finished, almost certainly not, and the damp does no harm. If rain fell on a fresh, unfinished surface it will have washed cement out and left a weakened, pitted top layer.