How long does concrete take to set?
Concrete doesn’t actually ever set entirely, although it does harden enough to allow you to walk on, or build on it.
Instead concrete goes through a chemical process known as curing. This is where the water reacts with the cement to harden the mixture, and make it the strong, load bearing material that is used in construction around the world. This curing process is continuous, so technically the concrete you lay will continue to gain strength for years to come.
However, after a few days you will be able to walk on your concrete, and after a few weeks it will be strong enough to build on.
Curing times for Concrete
Concrete mixes are categorised by their cured strength, such as C20 or C30. This means that after the initial curing period it will reach a strength of 20 or 30 Newtons, and so on. The strength is judged after 28 days, and regardless of how much it continues to cure or strengthen after this point, this 28-day period will provide the practical strength of the concrete.
Find out more about different concrete types and strengths here.
After 7 days curing the concrete will have reached 75% of the full strength it will reach after the 28 day period. Whilst this may provide enough compressive strength for some domestic and lightweight applications, it is still important to wait until the 28 day period is complete before commencing further heavy duty industrial builds, or driving heavy plant or equipment on it.
For lower strength domestic mixes, such as concrete that has been poured for driveways or garden projects, the concrete should be set enough to walk on after 24 to 48 hours. However, to ensure you don’t damage the concrete or effect the final finish, you should still wait 28 days to drive your car onto it.
Does curing take longer in summer?
Whilst some people may think concrete needs to ‘dry’, the chemical process known as curing is actually dependent on the water in the mix.This means that for the curing to complete properly, the concrete should not be allowed to dry out, or your concrete may crack. So, if you’re laying concrete in the middle of a heatwave, you may want to consider building a shade or structure over the top of the concrete to keep the moisture from evaporating.
As a result, if you’re laying concrete in very hot weather it is important that you keep your concrete hydrated to ensure the curing process doesn’t stop.
Can I lay Concrete in Winter?
It’s unlikely to get hot enough to affect your concrete very often in the UK, the bigger problem for us is that the concrete may get too wet! If there’s too much moisture, the concrete may become weak and brittle, leading to cracks.
Freezing temperatures can also affect the curing process as the water in the mix may freeze before the concrete has reached its full strength. In this case, you should consider insulating the concrete with blankets or polythene, and leaving the form work in place for as long as possible to provide an extra layer of protection.
Reach our tips for pumping concrete in cold weather to find out more.
It’s always best to get your concrete from a reputable supplier who can offer you professional advice for laying your concrete in any conditions. Simply contact the team at All Mix Concrete discuss your project with an expert.