Basics

The First Thirty Days of a New Slab

The pour is one morning. What happens over the weeks afterwards decides how strong the concrete actually ends up, and most of it is invisible, free, and easy to get wrong.

Updated October 2026 · Burlington Concrete

Almost everything written for homeowners about new concrete is a list of confident intervals. Wait this long to walk on it, that long to park on it, this long before sealing. We are not going to give you those numbers, and the reason is the point of this page. It applies to a drive, a patio and a garage or shed concrete slab alike.

Why there are no times on this page

Concrete gains strength through a chemical reaction, and the speed of that reaction depends on the mix that was ordered, the temperature on the day, the temperature every night since, the humidity, the wind, and how the slab was protected. Change any of those and the honest answer changes with it.

We hold ourselves to a simple rule here: no figure goes on the page without somewhere to point for it, and no such source exists for a universal interval. So the useful version is this: the crew who placed your concrete know the mix, saw the weather and protected the slab, and they can tell you. Ask them, and ask specifically about vehicles rather than accepting one answer covering both feet and cars.

It is not drying. It is reacting.

The single most useful idea here, and the one that makes the rest obvious.

Concrete does not harden by drying out. It hardens because cement and water react, and that reaction continues for a long time as long as there is water present to sustain it. Strength arrives gradually over that period rather than at a moment.

Which means letting a slab dry fast is not speeding anything up. It is stopping the reaction in the part that dried, and the part that dries first is the top surface: the bit you walk on, park on and salt. Lose that moisture early and the slab finishes with a skin measurably weaker than the body of concrete below it, which is precisely where flaking begins a few winters later.

What curing looks like when it is being done

This is worth knowing so you can recognise the difference between a crew finishing properly and a crew leaving.

Curing means keeping moisture in the slab. That can be a curing compound sprayed on, sheeting laid over, or keeping the surface damp, and any of them is fine. What is not fine is nothing at all on a bright breezy day.

It should also start promptly rather than the following morning, because the surface is most vulnerable in the first hours. Evenness matters too: cover one half of a slab and leave the other exposed and you have printed the difference into the concrete, where it will sit for months before weather softens it.

If nobody has mentioned curing to you, it is a fair question to ask before the crew packs up.

The things to keep off it

• Vehicles, longer than you think. Loading is a different threshold from walking, and turning a wheel while stationary concentrates force on one spot.
• Anything with a point. Ladder feet, a trailer jack, furniture legs, a bike stand. Young concrete marks.
• Sharp cleaning. No pressure washer, no acid, no aggressive scrubbing in the early weeks.
• Sealer, for now. Sealing a slab that is still giving up moisture traps that moisture underneath, which causes the problem you were sealing to prevent. It is a decision for later.
• Deicing chemicals, all of the first winter. The whole season, without exception.

The first winter, which is the real test

If your slab goes down in autumn, the first freezing season arrives while the concrete is still young, and that is the point at which most avoidable damage happens.

The rule is that nothing chemical goes on it. Rock salt is the obvious one. The trap is the advice that usually follows it. The chloride products sold as kinder to concrete sit on the industry's own list of what must never be applied to it, and in comparative testing the magnesium one finished last of all for loss of strength. A great deal of national guidance gets this exactly inverted.

Sand does nothing to the concrete and gives grip. A shovel does better than either, provided it is a plastic blade rather than a steel one being dragged across a young surface.

Rain, which worries people more than it should

A shower a day or two after a pour is generally harmless and occasionally helpful, since the slab wants moisture anyway. What causes damage is heavy rain landing on concrete that is still soft enough to be marked by it, which is a matter of hours rather than days, and a competent crew watches the forecast for exactly that window and covers the work if it has to.

The situation worth a call is standing water sitting on a new slab and not going anywhere. That is not usually a curing problem; it is early evidence that the falls are not doing what they should, and it is far easier to raise in week one than in year three when the same puddle has become a stain and a patch of scaling.

What is normal and not worth worrying about

A white powdery bloom after a few weeks is efflorescence, salts left behind as water leaves the slab, and it generally weathers away over the first season. Patchy colour that shifts around over a fortnight is moisture, not a defect. Fine lines appearing at the joints are the joints doing their job, and the page on jointing explains why that counts as good news.

What is worth a call is anything that has changed height: a corner that has dropped, an edge that has settled, or two sides of a joint no longer level. Those are ground problems rather than concrete ones, and what water does to a base sets out how they begin.

New work of any kind is on concrete slab, concrete patio and concrete driveway.