How Long Does Concrete Take To Dry?
Concrete hardens in a day or two but keeps curing for weeks so knowing the difference saves a cracked floor.
The short answer
Concrete takes 24 to 48 hours to dry enough to walk on when the mix is made correctly, and it reaches its full strength after around 28 days as it keeps curing. A thick slab or floor takes longer still to dry out right through, so wait before laying moisture-sensitive flooring and keep heavy loads off it for the first few weeks.
Once a concrete floor or base is down, it's tempting to walk across it, load it up or get the next stage of the job started straight away. Giving it time pays off, because concrete that's rushed ends up weaker and more likely to crack, and flooring laid on a damp slab can fail months later.
The photos in this guide come from a floor infill on one of our own DIY projects, and below we go through the difference between drying and curing, what speeds the process up or slows it down, and how to tell when your concrete is ready for the next step.
The Difference Between Concrete Drying And Curing
Drying and curing happen at the same time, but they're two separate processes. Curing is the chemical reaction between cement and water that makes concrete hard and strong. Drying is the spare water that wasn't used in that reaction slowly evaporating out through the surface.
Curing needs moisture, so concrete keeps gaining strength for as long as there's water in the mix to feed the reaction. If the surface dries out too fast in the first few days, through hot sun, wind or too much heat indoors, the top layer stops curing properly and ends up weak, dusty or cracked. That's why you want concrete to dry steadily rather than quickly.
What Affects How Long Concrete Takes To Dry
No two pours dry at exactly the same rate. These are the things that make the biggest difference:
- Water in the mix: A wet, sloppy mix has more spare water to lose, so it takes longer to dry and ends up weaker, with a surface that can flake once it's hard. Too little water makes the concrete hard to compact and finish. Our guide on how to make concrete with the right mix covers getting it right.
- Thickness: A thin path dries much faster than a deep slab or a filled-in floor, because the water in the middle has further to travel.
- Temperature: Warmth speeds drying up and cold slows it right down. Concrete that freezes before it's set can be ruined, so protect it on frosty nights.
- Humidity and airflow: Damp, still air slows evaporation, while moving air or a dehumidifier speeds it up.
- The type of mix: Some ready-mixed and bagged concretes are made to set faster, and you can add an accelerator to a site mix when time is tight.
How Long Does Concrete Take To Fully Dry Out?
In our experience, concrete that's been mixed correctly is dry enough to walk on within 24 to 48 hours. At that stage it's hard on the surface but still curing and drying underneath, so treat it gently and keep heavy loads, vehicles and wheelbarrows of materials off it.
The concrete carries on gaining strength every day after that and reaches its full design strength at around 28 days. Fully drying out is a separate matter. A deep slab or floor infill can hold moisture for well beyond those four weeks, especially indoors in winter, so check it before laying anything that's sensitive to damp.
- Walking on it: 24 to 48 hours
- Next stage of work: A few days, depending on thickness and weather
- Full strength: Around 28 days
- Timber or vinyl flooring: Test with a moisture tester, as thick slabs take longer than 28 days
How To Tell If Concrete Is Dry
You can't judge how dry concrete is all the way through by looking at the surface alone. The only reliable way is a moisture tester or a hygrometer test, which is what flooring fitters use before laying timber, laminate or vinyl over a new slab.
The colour is a useful first sign, though. Wet concrete is dark grey, and as the water evaporates it turns paler and patchier. The photos below are from a floor infill on that project, between new stud walls and the old quarry tiles. The first shows it freshly laid, and the second shows the same floor after 48 hours, when it had lightened noticeably but was still damp lower down.
If any part of the surface still looks dark or feels cold and damp, hold off laying slabs, tiles or flooring. The same goes for a coat of self-levelling compound across the floor, which needs a sound, dry base to bond to.
How To Speed Up Concrete Drying Safely
When you're up against a deadline, you can help concrete along, but the aim is steady drying rather than baking it. Push it too hard and you'll get cracks and a weak, dusty surface.
- Get the mix right from the start, without adding extra water to make it easier to work.
- Use a quick-setting concrete or add an accelerator to the mix if you know time is short.
- Keep the air moving with windows open, and run a dehumidifier to pull moisture out of the room once the surface has hardened.
- Put the central heating on low indoors rather than pointing heaters at the slab.
- Leave the surface uncovered once it has cured for a few days, so the water can escape. Sealers and flooring trap moisture in.
- Use a concrete blanket or insulation boards in cold weather to stop frost damage and keep the curing going.
In hot, sunny or windy weather, the opposite applies for the first few days. Covering fresh concrete with polythene or misting it with water slows the surface drying so it cures properly, and you can let it dry out once it's hard.
Planning Around Concrete Drying Times
Build the drying time into your plans from the start. For a garden base or path, that means mixing and laying concrete when the forecast is mild and dry for a couple of days. For fence posts, the concrete needs to firm up before the panels go on, and our comparison of concrete or wooden fence posts looks at that job in more detail.
Indoors, allow the extra weeks a thick floor needs before fitting flooring or installing underfloor heating over it. Concrete that's given time to cure and dry is stronger, flatter and far less likely to cause problems later.
More Questions Answered
Can you walk on concrete after 24 hours?
Yes, you can walk carefully on concrete after 24 hours in most conditions, as long as it was mixed properly and the weather hasn't been cold. Stick to light foot traffic and avoid twisting, dragging tools or putting down heavy loads. In cold or damp weather, wait closer to 48 hours, and keep cars off a driveway for at least a week.
What happens if it rains on fresh concrete?
Rain on concrete that's only just been laid can wash out the cement on top and leave a pitted, weak surface. Once the concrete has started to set, after a few hours in mild weather, light rain does little harm. Cover fresh concrete with polythene if rain is forecast, keeping the sheet off the surface with timber so it doesn't mark the finish.
How long does concrete take to dry in cold weather?
Concrete takes noticeably longer to set and dry in cold weather, because low temperatures slow the curing reaction. It can take several days before it's firm enough to walk on in winter. Frost is the bigger risk, as water freezing in fresh concrete damages it, so avoid pouring when frost is forecast and protect new concrete with a blanket or insulation boards.
Should you water new concrete?
Watering new concrete helps it cure properly in hot, dry or windy weather, because it stops the surface drying out before the cement has fully reacted. Lightly mist the surface once it has hardened enough not to mark, or cover it with polythene to hold the moisture in. In cool, damp UK weather, it isn't needed.
How do I know when a concrete floor is dry enough for flooring?
Check it with a moisture tester or a hygrometer test before any timber, laminate or vinyl goes down, as a slab can look dry on top while it's still damp lower down. Flooring fitters test a new slab the same way. A paler, patchier colour tells you drying has started, but thick slabs take longer than 28 days to dry right through.
Is it a problem if I make the concrete mix too wet?
Yes. Every drop of spare water has to evaporate before the concrete is dry, so a sloppy mix takes longer, ends up weaker and can leave a surface that flakes once it's hard. Topping up the water to make the mix easier to work is the mistake to avoid. Go too dry, though, and it won't compact or finish well, so aim for the right mix.
Can I point a heater at concrete to dry it faster?
No. Concrete wants steady drying rather than baking, and blasting it with heat leaves you with cracks and a weak, dusty surface. Indoors, keep the central heating on low, open the windows to get air moving and run a dehumidifier once the surface has hardened.
What's the difference between concrete drying and curing?
Curing is the chemical reaction between cement and water that hardens concrete and gives it strength. Drying is the leftover water evaporating out through the surface. The two happen side by side, and the concrete only keeps gaining strength while there's water to feed the reaction, which is why a surface that dries too fast in the first few days ends up weak, dusty or cracked.
Dave, or Demolition Dave as the team calls him, worked as a builder for over 10 years before joining DIY Works. He now concentrates on his own properties and writes most of our construction content, along with tools, carpentry and plenty more.