Concrete is a durable, attractive and beautiful construction material. But what happens after you pour concrete? It takes almost 28 days for concrete to form from the chemical reaction of cement and water. You want to maintain moisture in concrete during this process, also known as hydration. Water vaporizing too fast from the concrete surface, which can easily happen outdoors or in direct sunlight, will weaken the final product and cause cracking and stresses.
Priority should be given to controlling the temperature and moisture of the concrete during curing. Concrete mix can be strengthened and more resilient to future cracking by being given extra attention after it has been poured. Before you start your next project, make sure to review our list of the worst and best concrete-curing methods.
- DO spray concrete with water.
For the first seven days, a common method for curing concrete is to frequently hose it with water. This can be done five to 10 times per daily or as often as possible. This is known as “moist cure” and allows moisture to evaporate slowly. Concrete that has been moistened and cured can be up to 50% stronger than concrete that is not. Concrete poured in cold weather is not recommended to be sprayed. However, you can see the “Don’t Let Concrete Get too Cold” section below.
- DO COVER NEW CONCRETE.
If you don’t have the time or patience to visit your concrete as often as is necessary to ensure true moist curing, you can use a cover to slow down the evaporation. You can use either a polyethylene sheeting at least 4mm thick, or a concrete curing insulation blanket. Both are available from DIY shops. To cover the concrete, thoroughly wet it. Next, use bricks, rocks or other heavy objects to secure it. Everyday, remove the blanket or sheeting, then wet the concrete once more, then re-cover the concrete. This process can be repeated for seven days. You can also use this technique for concrete columns or walls. Simply wet them and wrap them in plastic sheeting or a curing blanket.
- DO NOT pond cure concrete slabs
Concrete cures can also be done by pond curing. The process involves forming temporary berms around new concrete slabs and then flooding the surrounding area with water. The work of seven days worth of moist curing is completed in three days with pond curing. It doesn’t require daily attention. Just make sure that the water level does not drop below the concrete slab. You’ll need to replenish the water level if it falls. It is not a good choice as it requires a lot of soil to create berms around large concrete slabs. This method may be used by large-scale builders to speed up construction, such as pouring foundation slabs.
- Do not forget to apply a curing agent.
Curing compounds are an alternative to other methods. These are available from ready-mix concrete companies and DIY stores. They contain soluble emulsions which form a protective layer when they are sprayed onto freshly poured concrete slabs. The film acts as a barrier to water evaporation and allows concrete to cure at a constant rate. Some curing compounds will disintegrate in a few weeks. Others should be removed with scrubbing once the curing process has completed. Quikrete Acrylic Concrete Cure & Seal penetrates concrete and acts as a permanent sealer. Concrete will look fresh poured again thanks to this sealer. To ensure you are satisfied with the curing compound, make sure to read all labels.
Concrete slabs should not be left without control joints.
Concrete installation should produce a high quality product that resists cracking. Although curing concrete can help strengthen the project, concrete slabs can still crack despite all precautions. This is due to concrete shrinkage caused by temperature fluctuations and water consumption during hydration. Do-it-yourselfers can create control joints to help guide cracks. The control joints should be cut to a quarter of concrete slab’s depth at the beginning of curing, and within 24 hours. The control joints can easily be cut in the concrete slab using a metal jointing instrument.
The maximum distance between joints (in feet), can be determined by multiplying the concrete thickness (in inches) by 2.5. To get a distance between the joints of a sidewalk with a depth of 4 inches, multiply 4 times 2.5. For crack protection, you can place them closer together. For larger slabs, such as patios, it is a good idea to break the concrete with joints that are perpendicular. These should be done down as well as across. If your slab patio, driveway or sidewalk cracks it will likely be along a precut joint. This allows for almost no notice.
- Don’t let concrete get too cold.
Concrete is best when the temperatures are above 50 degrees for 5 to 7 days. However, plans can be ruined by an unexpected cold front. It is important to keep concrete moist, but not too warm that it stops the chemical hardening process. Concrete’s chemical reaction slows down at 50 degrees Fahrenheit. It stops completely at 45 degrees Fahrenheit. Concrete will go dormant, and its strength won’t increase. Concrete can only be poured and used in a few days. Concrete insulating blankets or, in an emergency, old household blankets should be used to cover new concrete when temperatures drop. For the first 2 to 3 days, or up to a week if it is very cold, protect concrete. After that it should be strong enough for you to handle without any damage.
- Do not paint concrete or stain it within the first month.
Concrete’s chemical composition and residual moisture can cause concrete to harden faster than it is ready for paint. It takes approximately a month for all the water to evaporate during the hydration process. If you apply paint too quickly while moisture is still rising on the surface, it can cause paint to crack or peel off the bond. Paint may not stick as well and stained concrete’s final color or appearance may be affected. For best results, wait 28 days before applying paint or stain. Then, follow these top tips from Quikrete concrete professionals.
- Do not place concrete under excessive weight.