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You may rightly consider concrete to be one of the most durable and attractive construction materials around, but did you know that everything you do after pouring has just as much impact on its strength as the mixing process? In fact, the chemical reaction between cement and water that binds sand and gravel together to make concrete takes nearly 28 days to fully complete. During this process, which is known as hydration, you want to keep moisture in the concrete. Otherwise, water evaporating too quickly from the surface—which can happen easily outdoors and in direct sun—will weaken the finished product with stresses and cracking.
Controlling the moisture content and the temperature of the new concrete for the first several days through curing take top priority. By giving concrete mix extra attention during this period rather than walking away as soon as it’s poured, you can increase the structural integrity of the concrete and make it more resistant to future cracking. For the best results, check out our list of best (and worst) concrete-curing practices before you tackle your next project.
DO spray new concrete with water.
One of the most common methods for curing concrete is to hose it down frequently with water—five to 10 times per day, or as often as you can—for the first seven days. Known as “moist curing,” this allows the moisture in the concrete to evaporate slowly. Moist-cured concrete can be up to 50 percent stronger than concrete that was cured without being dampened! Spraying is not recommended for concrete poured during cold weather, however; for pours in chilly weather, see “Don’t Let Concrete Get Too Cold,” below.
DO cover new concrete.
When you don’t have time to revisit your concrete with a hose as many times as necessary for true moist curing, another option is to use a cover that can trap and slow the evaporation of the moisture in the mix. Either polyethylene sheeting that’s at least 4mm thick or a concrete curing insulating blanket—both available from DIY stores—are good for this task. Wet the concrete thoroughly, and then cover it with the sheeting of your choice, using bricks, rocks, or other heavy items to hold it in place. Remove the sheeting or blanket daily, wet the concrete again, re-cover it, and repeat for seven days. This technique can also be used for upright concrete columns and walls by wetting them down and wrapping them with a curing blanket or plastic sheeting.
DO pond cure concrete slabs.
Pond curing is another great way to cure concrete, and the process is just as it sounds: You form temporary berms around a new concrete slab, and then flood the area inside them with one foot of water. Three days of pond curing does the work of sevendays of moist curing, and without daily attention—just be sure the water level remains above the concrete slab.If it drops, you’ll need to refill a little. This technique isn’t for everyone,though, because it takes quite a bit of soil to form berms around a big concrete slab. Large-scale builders may use this method to speed up the construction process when pouring foundation slabs, for example, in order to get on to framing the structure.
DO make the process easier by applying a curing compound.
If other methods are not feasible, there’s a simpler solution yet: curing compounds. Available from DIY stores and ready-mix concrete companies, these contain soluble emulsions that form a protective film when sprayed directly onto the surface of newly poured concrete slabs or walls. Ultimately, the film provides a barrier or film to prevent water from evaporating, allowing it to cure at a consistent rate. Some curing compounds are designed to disintegrate completely after a couple of weeks, while others should be removed by scrubbing after the curing process is complete. Still others, such asQuikrete Acrylic Concrete Cure &Seal,penetrate the surface of the concrete, becoming a permanent sealer that waterproofs the concrete to keep it looking freshly poured. Read the manufacturer’s labels carefully before choosing a curing compound to ensure that it meets your specific needs.
DON’Tskip control joints in concrete slabs.
The goal of all concrete installation is to produce a high-quality product that resists cracking. While curing concrete will go a long way toward strengthening the finished project, many concrete slabs will crack anyway—despite all precautions—due to concrete shrinkage as water is used up in the hydration process as well as temperature fluctuations. To preserve the beauty of the slab in the face of these challenges, do-it-yourselfers can place control joints at predetermined locations to guide the inevitable cracks. These joints should be cut in a quarter of the depth of the concrete slab during the very beginning of the curing process, within 24 hours of the initial pour. Usinga metal jointing tool, the control joints can be easily and smoothly cutinto the concrete surface as the appropriate distances in the slab.
Determine the maximum spacing between joints (in feet) by multiplying the planned concrete thickness (in inches) by 2.5. For example, if you’re creating a sidewalk that is 4 inches deep, you’d multiply 4 by 2.5 to get a distance of 10 feet between joints. Feel free to place them closer together for added crack protection. On a larger square slab, like a patio, you’ll want to consider breaking the concrete with joints that are perpendicular, too—down as well as across. Then, if your slab patio, driveway, or sidewalk cracks, it will most likely do so along a precut joint and can, therefore, go virtually unnoticed.
Photo: doitbest.com
DON’Tlet new concrete get too cold.
The best time to pour concrete is when temperatures are expected to remain above 50 degrees for five to seven days, but plans can go awry with the arrival of an unexpected cold front. When that happens, the importance shifts from keeping the concrete damp to keeping it warm enough that the chemical hardening process is not interrupted. Concrete’s chemical reaction slows at 50 degrees Fahrenheit and completely stops at 45 degrees Fahrenheit, meaning that it’ll go dormant and it won’t gain strength. If you expect to pour concrete and use it in a couple days, you can’t. When the temperatures drop, new concrete should be covered with concrete insulating blankets (or, in a pinch, old household blankets!). Protect new concrete from the cold for the first two to three days—up to a week, if it’s very cold—after which it should be strong enough to handle it without risk of damage.
DON’T paint or stain concretein the first month.
Any paint or stain applied to young concrete while it’s still hardening can be negatively affected by residual moisture or the changing chemical content in the concrete. It takes about a month for all of the water to get used up in the hydration process. Brush on paint too soon while moisture is still rising to the surface, and it can put pressure underneath the hard barrier of paint, causing it to peel away or break the bond. For this reason, paint may not adhere as well, and the final color and appearance of stained concrete may also be affected. To achieve the best results, wait until the 28-day period is over to apply paint or stain, and then follow the top tips outlined in this video from the concrete pros at Quikrete.
DON’T subject new concrete to excessive weight.
Although concrete will harden soon after pouring, it’s still susceptible to damage from weight during the first four weeks. Wait at least 24 hours before allowing foot traffic, including pets, on a newly poured sidewalk or slab, and don’t drive a vehicle on a new driveway for at least 10 days. After that, you can drive regular passenger cars on the concrete; heavy pickups or RVs can roll onto the driveway once the concrete reaches its full strength, at around 28 days.
This content has been brought to you by Quikrete. Its facts and opinions are those of BobVila.com.
FAQs
Can you over water curing concrete? ›
Keeping concrete moist is essential to the concrete curing process, but too much water and the concrete may not form in the way it needs to. If it loses too much moisture through evaporation, it will not cure properly and will become prone to cracks.
Should concrete be covered when curing? ›Covering the curing concrete with plastic keeps it cleaner, but there is a more important purpose behind this practice. Water is mixed into concrete to activate the cement binding agent and as the mix dries, it hardens. The drying, or "curing," should be gradual, otherwise cracking may occur.
Should I spray water on fresh concrete? ›Properly curing your concrete improves strength, durability, water tightness, and resistance for many years. The first 7 days after installation you should spray the slab with water 5-10 times per day, or as often as possible. Once the concrete is poured the curing process begins immediately.
How often should you water cure concrete? ›Moist curing is a common method of concrete curing. It involves wetting the concrete slab often with water (5-7 times per day) for the first 7 days. This method ensures your concrete slab will be extremely strong and durable, because it allows the moisture to evaporate slowly, preventing cracks and shrinks.
How long does it take for 4 inch concrete to cure? ›Concrete typically takes 24 to 48 hours to dry enough for you to walk or drive on it. However, concrete drying is a continuous and fluid event, and usually reaches its full effective strength after about 28 days.
What might happen if heavy rain falls 5 hours after concrete is poured? ›Even if it starts raining after a concrete pour, the potential for damage may not be that serious. If you had time to complete the finishing process and the concrete has stiffened (typically 4 to 8 hours after mixing), rainwater may cause little if any damage.
What happens if you don't water concrete? ›Water facilitates the curing and hardening processes. Without it, the chemical reactions needed to form the hard crystals that give the concrete its strength can't take place. Too little water leads to structurally weak concrete, and too much will disrupt effective curing and cause flaking, shrinking, divots or cracks.
What days are the most critical when curing concrete? ›After concrete is placed, the concrete increases in strength very quickly for a period of 3-7 days. Concrete which is moist cured for 7 days is about 50% stronger than uncured concrete.
How long should concrete cure before putting weight on it? ›Curing time of concrete is typically 24-48 hours, at which point it's safe for normal foot traffic. After one week, concrete is typically cured enough to handle continued construction including heavy machinery. Concrete is recognized to have reached full strength 28 days after placement.
Will rain ruin fresh concrete? ›Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish.
How strong is concrete after 3 days? ›
Viewing the table, you can discover that concrete gains 16 percent strength in one day, 40 percent in 3 days, 65 percent in 7 days, 90 percent in 14 days and 99 percent strength in 28 days. Therefore, concrete gains strength rapidly in the first two weeks after casting (90% in just 14 days).
Why does new concrete crack? ›As the slab loses moisture while curing it gets a bit smaller. As the concrete shrinks, the slab could crack in order to relieve tension. Shrinkage cracks are common and can occur as early as a few hours after the slab has been poured and finished. Usually they are not a threat to the structure.
Does thicker concrete take longer to cure? ›Thickness of the concrete slab - Thicker slabs will take longer to dry obviously. However, this is not linear; a 4 inch thick slab will not cure 4 times slower than a 1 inch thick slab, although that is the current rule of thumb.
How long should concrete cure before removing forms? ›After pouring and finishing the slab, you should wait 24-48 hours before removing concrete forms. You can remove the formwork once the concrete has enough strength to keep it from cracking. Concrete naturally contracts as it cures, so it should pull away from the forms and make them easier to remove.
Which is the best method of curing? ›Water curing, if properly carried out, can be the most efficient - and the most appropriate for some types of work, e.g. floors, and include ponding, sprinkling, and wet coverings. On flat surfaces such as pavements, footpaths, and floors, concrete can be cured by ponding.
How can I make my concrete cure faster? ›- Weather is a factor. If your concrete is exposed to the elements, you won't be surprised to learn that the concrete will dry faster in warmer, sunnier conditions. ...
- Using a heater. ...
- Using warm water. ...
- Reducing the amount of water. ...
- Avoid hard trowelling.
Does concrete take 100 years to cure? No, this is a bit of a myth with the concrete industry. While concrete does continue to harden indefinitely, pore moisture has to drop below a certain level at some point and this isn't typically 100 years.
Can you walk on concrete after 12 hours? ›After 24 hours, you can safely walk on your new concrete.
If there has been a lot of rain or you've done decorative stamping in the concrete, you should wait longer. Normal foot traffic should be fine on standard concrete at this point, but you should still be cautious about damaging the surface of the new paths.
Yes, you can pour fresh concrete over existing concrete. As long as your concrete is in mint condition, this task is doable. If you decide to pour a new mixture over an old slab, be sure it is at least 2 inches thick.
How much weight can a 4 inch concrete driveway hold? ›Concrete driveways are typically poured four inches thick, giving the concrete driveway enough strength to withstand loads of regular vehicles (up to approximately 8,000lbs).
Is it OK if it rains 24 hours after pouring concrete? ›
Concrete typically needs 24 to 48 hours to dry.
If the rain comes before the 24-hour mark, you may risk your concrete getting damaged. The time it takes to dry depends on the thickness and size of the concrete project you are attempting to take on.
When concrete is not cured properly, its durability, strength and abrasive resistance are affected. Due to inadequate curing, concrete develops plastic shrinkage cracks, thermal cracks, along with a considerable loss in the strength of the surface layer.
What causes concrete not to cure? ›Moisture plays a critical role in curing time for concrete. If there is not sufficient water in the mix, the concrete will cure too fast, resulting in weaker overall strength. Too much moisture, often used in the finishing step will weaken the top layer and cause flaking.
What are the failures caused by improper curing? ›Improper curing leads to reduced compressive strength development and increased drying shrinkage. Sorptivity and permeability values were increased. This is due to reduced levels of cement hydration, as water evaporates from the concrete surface.
Does concrete cure better in hot weather? ›In colder temps, the concrete takes longer to set allowing the crystals formed within the concrete more time to strengthen. Conversely, warmer temps mean that crystals form more quickly, allowing for less time to strengthen. For example, at 100 degrees Fahrenheit, concrete could set in as little as two hours.
Does concrete cure better in hot or cold? ›Concrete sets and forms best between 50 and 60 degrees Fahrenheit. Concrete will cure at 30 degrees, and if the air temperature is between 30 and 40 degrees, you'll want to make sure your mixed concrete maintains a temperature of between 55 and 60 degrees.
Can you walk on curing concrete? ›Although concrete will harden soon after pouring, it's still susceptible to damage from weight during the first four weeks. Wait at least 24 hours before allowing foot traffic, including pets, on a newly poured sidewalk or slab, and don't drive a vehicle on a new driveway for at least 10 days.
What happens when you finish concrete too soon? ›More often, premature finishing or improper first (bull floating) or second floating results in trapping rising bleed water and air below the top surface of the concrete (Image 2). When this occurs, the resulting weak or soft zone below the surface causes the top surface of the concrete to flake or scale off.
Can I drive on concrete after 3 days? ›After 48 hours: Concrete is okay to walk on, but it's still curing and gaining strength. Keep all wheeled traffic, including cars, bicycles and skateboards, off the surface. After 7 to 10 days: At this point the concrete has gained enough strength to support a car.
What might happen if heavy rain falls 10 hours after concrete is poured? ›Will rain damage concrete after 12 hours? Rain falling on top of freshly laid concrete can damage the surface and compromise a level and floated finish. Even worse, if too much extra water works its way into the concrete mix, this can result in weak concrete overall.
What happens if you pour concrete and then it rains? ›
If too much rain falls into the concrete mix – or if it is laid onto wet surfaces or trenches – this will affect the mix, resulting in weak concrete. Rain falling on freshly-poured concrete can cause damage to the surface, making it bumpy and uneven.
Is it OK to pour concrete on wet ground? ›Damp ground will not be a problem unless is can not support the weight of the concrete. Cement/concrete does not "dry" , it cures , a chemical reaction. It absorbs water to cure, as noted , some concrete applications are sprayed with water to aid the cure. Actually, concrete does “dry” in the curing process.
Can you drive on concrete after 4 days? ›Do not drive on the concrete for the first 7 days. Leave the warning tape in place to let delivery vehicles and others know that they need to stay off your concrete. After One Week – After 7 days, it's OK to drive on your new concrete with normal passenger vehicles.
How soon after pouring concrete can you build on it? ›Some companies say that you should wait a full 48-60 days to be safe. However, that may vary depending on many of the factors in this guide. You can start framing on a poured concrete slab about seven days after it's poured when it's close to 75% cured.
Should you fix hairline cracks in concrete? ›Hairline cracks that are only seen from inside the home or on the surface of patios and sidewalks are generally safe and can be filled to prevent water from entering the area, causing further deterioration.
Does rebar prevent cracking concrete? ›Rebar, or reinforcing bar, is a common feature of many concrete applications. Its primary purpose is to increase the tensile strength of the concrete, helping it resist cracking and breaking. With greater tensile strength, concrete is better able to resist breaking under tension.
How do you determine when concrete is dry? ›Evaporation rate 15 g/m2/24 hours
But because the rate of evaporation falls as concrete dries, the test method ASTM F1869-04 can work to measure this rate of evaporation. If the evaporation rate is found to be below 15 g/m2/24 hours, it is usually taken as indicating that the concrete moisture content is below 5.5%.
Upon pouring and throughout curing, the concrete must be kept at 40 degrees if more than 72 inches thick, 45 degrees if 36 to 72 inches thick, 50 degrees if 12 to 36 inches thick, or 55 degrees if less than 12 inches.
Can you finish concrete after it dries? ›Finish by fine-tuning with light sandpaper, until the surface is perfectly smooth. We recommend using a hand planer to smooth and compact the surface. If the concrete dries a lot then we recommend that you add water to the surface, this will help you give it a good finish.
How long do you wait to float concrete? ›Darbying or bull floating should be done immediately after "screeding", or after the concrete has been tamped if tamping was done. This process should be finished before excess moisture or bleedwater appear on the surface.
Should I spray water on new concrete? ›
Properly curing your concrete improves strength, durability, water tightness, and resistance for many years. The first 7 days after installation you should spray the slab with water 5-10 times per day, or as often as possible. Once the concrete is poured the curing process begins immediately.
How long does 4 inches of concrete take to cure? ›The general rule of thumb is that concrete takes about 28 days to dry for every inch of slab thickness.
What are four methods for properly curing concrete? ›Conventional methods for curing concrete
Water curing by ponding, sprinkling or immersion. Covering with wet burlap, plastic film or reinforced paper.
After concrete is placed, the concrete increases in strength very quickly for a period of 3-7 days. Concrete which is moist cured for 7 days is about 50% stronger than uncured concrete. Water curing can be done after the slab pour by building dams with soil around the house and flooding the slab.
How long before concrete can be rained on? ›As long as the concrete is given 4 to 8 hours after mixing and finishing to set up, rainwater won't affect it nearly as badly as it could. Some concrete mixes will actually benefit from rainwater on the surface because it's beneficial in aiding the hydration and curing process.
What happens if you don't water new concrete? ›Concrete that is not moist-cured at all dries too rapidly, and reaches less than half its potential design strength. It will also have a greater number of shrinkage cracks.
When should I start watering my concrete slab? ›In short, the curing should start after minimum six hours (Final setting time of cement) and not less than 24 hours.
What is the best weather to pour concrete? ›Elements like volume changes, cracking, humidity, wind speed, and temperature all should be accounted for when pouring concrete. Experts agree that the best temperature for pouring concrete is between 40 °F and 60 °F.