Concrete is used in all types of construction for many decades. Yet we always keep asking the same question: how long does it take for concrete to dry and completely cure?
Owners and clients are desperate to continue using their amenities at full potential and cannot wait unit poured mixture becomes hard enough to walk or drive on.
Good quality concrete takes up to 48 hours to dry for people to easily walk on it without damaging the structure or leaving foot prints. To completely cure and set into hardest substance concrete needs 28 full days. Weather conditions and quality of mix may affect this time.
Just because it takes concrete almost a month to cure it does not mean you cannot use it. Construction or use can carry on, but it will reach its strongest point after 28 days.
Time-lapse of Concrete Cure
It is a fact that concrete mixture continues to cure with time and gets harder every day. Stop guessing and know all details about drying and using freshly poured concrete into forms.
How does curing process actually work and what can you continue doing after certain period of time?
|Time||Full Strength||Construction and Performance|
|2 Days||30%||Walk on / Take off Forms|
|7 Days||65%||Drive on / Frame on Top|
|14 Days||90%||Average Size Foundation Walls|
|28 Days||99%||Most Complicated Construction|
We have to add that each project with concrete is specifically designed by structurally engineer. Thickness, rebar, ties and structural components are calculated before installation. This table is just to show relevant time of use.
Day 2 – It takes only that long for mix to get sold hard. Trades can remove forms on small or medium projects and you can easily walk on it without leaving foot prints.
Interior non-structural concrete works can be covered up and forms taken out for non-commercial use. Typically footings, sidewalks, home driveways are stripped but continue to cure.
Day 7 – You can drive on concrete and continue building small or medium structures. Concrete has reached more than half of its planned strength and if you slowly continue adding pressure to it nothing will happen.
7 days curing process is enough for small residential building foundation walls, basement and house garage slabs, stairs or porches.
Day 14 – Most of work is carried on after this time period. Construction companies are fine with 90% strength of product and place forms, rebar, additional structural loads on top.
Who usually waits 14 days for concrete structure to cure? Condo/apartment building after completion bottom levels, tunnels, large buildings and facilities.
Day 28 – At this point concrete is 99% cured and slowly continues to get stronger. Basically it doesn’t get better than this and any construction use can be carried on.
Full period of 28 days may be required by engineers for development of complicated bridges, constructions on height, mountain projects or under water facilitates.
Difference between Concrete Drying and Curing
Very often people don’t fully understand chemical reaction of concrete and mix up curing process with drying. Also process of drying in concrete is different from what we usually think of.
Curing is factor of straightening and getting harder in time, while drying of concrete means evaporation of water.
Concrete Curing – Process of hardening with adequate temperature, level of moisture and application techniques. Concrete cures within 28 day to its 99% strength.
Concrete Drying – Mix looses base water and turning into rock solid state. Full vaporization of water can be several month and calculated to be 1 inch thickness for 30 days.
Just because concrete driveway or sidewalk is hard enough to walk on does not mean it is fully dry. Technically speaking drying process is even longer than curing and each inch of concrete in thickness fully loses water within 30 days.
How Can You Help Concrete To Dry Faster?
Every year we learn something new about construction industry and materials that have been in use for centuries. With technology progress we can control chemical process better.
- Initial Amount of Water in Mix
- Air Circulation Inside the Building
- Reduce Amount of Water in Air
- Less Smoothening The Surface
Be very careful with every method of making the concrete dry sooner. Potentially fast evaporation can create tracks and other ways of damaging structure. We always recommend letting it dry under normal conditions and avoiding interference when possible.
Initial Amount of Water in Mix – if rate of water added is higher than normal, it would exponentially increase the time of vaporizing. Both curing and drying time would be affected.
Know what quality and rate of concrete to get for your job and how it will change dry time of cement. On average 15% – 20% of water is used in good mix.
Air Circulation Inside the Building – Good practice to keep exchanging fresh air is to have windows and doors open. If weather is too cold or too humid for concrete to dry, close everything and turn on furnace/AC.
For obvious reasons there is no need to do anything outside. Without intervention nature with winds will do everything for us.
Reduce Amount of Water in Air – it would make perfect sense to remove water from air if we are trying to dry up concrete.
Inside its better to use dehumidifiers, while outside concrete can be covered with certain materials. Some recommend covering it with hey or wool base tarps that trap moisture inside.
Less Smoothening the Surface – Although it’s not ethical in concrete world to in some projects leave surface alone, it works best for drying up.
Over troweling keeps water under secured layer of finished concrete and later on it will have harder time escaping.
Using this logic, rough concrete works like footings, pads or deck posts dry up fast; while finished concrete surface such as stairs will take longer to dry.
How to Accelerate Concrete Curing?
Although we have stated base of how long it takes concrete to cure, there are ways to accelerate the process and builders all over the world are doing it.
Remodel On Point have 4 ways in mind to speed up the process and they are not complicated.
- Using Worm Water in Mix
- Controlling Temperature
- Avoiding Weather Factors
- Adding Chemicals
First three ways to speed up concrete setting also help preventing from cracks. Last method is rarely used in industry, only when very specific project requires immediate curing of certain parts.
Using Worm Water in Mix – not many of us know, but simple temperature change in original concrete mix makes a big difference.
Worm water helps it cure faster. It won’t affect time by more than several percent, but every bit helps.
Controlling Temperature – Cold weather slows down curing and indoor heaters are recommended to get the process going.
Overheating freshly poured concrete can create problems too. Outdoor during hot summer cover it up and create shade.
Avoiding Weather Factors – Whenever working outside it would be beneficial for the mix to create a barrier from nature.
It could be something simple like covering with tarp and protection from light rain to complicated wood structures that literally enclose project area.
Adding Chemicals – Chemistry and understanding bounds has brought us long way. Now we can add specific chemicals just before pouring to help set much faster.
As we previously explained the best agent for accelerating concrete setting is calcium chloride.
Exceptions of Concrete and Mixes that Dry Fast
How come we hear advertising that hardware stores sell concrete products with curing time under 1 hour? Is it really true and how than why it is not used all over construction industry?
Yes there are products on market that can set as they claim within 20-40 minutes. They sell in small bags of 40-50 pounds on shelves and are not used in large construction projects.
In these mixes different accelerators and ingredients are added to speed up drying process. Calcium chloride is one of the popular accelerators for fast setting concrete.
Unfortunately we cannot use something like this in commercial or large projects. Setting and drying process is too quick. Sometimes it takes hours to deliver ready mix on jobsite, an hour to pour and same time to properly distribute or level concrete.