Cracking Concrete: How Quickly Does It Happen?

Cracking in concrete is a common occurrence, and it can begin as soon as 12 hours after the finishing process. Weather conditions can either slow down or speed up the process. Shrinkage cracking is usually planned for and handled with control joints. Control joints are one way to manage cracks in concrete. In about a month, fine cracks should disappear.

While shrinkage cracks can appear on the surface within hours of pouring concrete, it takes a full month for new concrete to fully settle. Crust cracking usually happens during the concrete stamping process, which is a way of adding texture or pattern to concrete surfaces. On sunny or windy days, where the top of the slab dries faster than the bottom, the top of the concrete surface may become crusty. When the seal is embedded, it separates the surface near the stamped joints and causes small cracks around the outer edges of the “stones”.

Although they don't look very good, crusting is not a structural problem that needs to be considered. The most common reason for concrete cracking is shrinkage. When your patio or driveway is poured, it is in liquid form so that it can form properly. As the concrete begins to dry, the water inside will evaporate and, as it does, the concrete will start to shrink. A concrete slab will shrink approximately ¼ inch per 100 square feet of floor space.

When concrete dries and shrinks, cracks can occur hours after pouring. Any 1/8 inch or smaller crack in your yard or driveway is considered standard. Some fine cracks may form and disappear after a month or two. To prevent this from happening, cover the concrete with an insulating plastic sheet or even straw to trap moisture and help the concrete cure at an even rate. Even if concrete cures slowly as described above, a large slab, such as a patio or sidewalk, may crack as a result of concrete shrinkage that occurs as temperatures change and water is depleted in the hydration process.

Cracks in concrete may not appear for years and can be caused by factors such as weather, sedimentation, and placing heavy objects on the concrete. In addition to these traditional curing methods, concrete additives and curing compounds can help concrete cure faster and withstand cold temperatures. It's important for contractors to follow well-established guidelines regarding concrete placement. Pouring a concrete slab of any type that is strong, looks good, and without imperfections doesn't just happen - it takes good preparation and workers qualified to do it right. When you hear that a concrete mix has a strength of 2000, 3000, 4000, or more than 5000 PSI, it refers to the pounds per square inch that would be needed to crush that concrete slab. It may be tempting to add more water to make it easier to work with but this is a mistake and cracks could form and greatly reduce the strength of the concrete. Quikrete offers a range of solutions for all types of cracks including its new line of advanced polymeric sealants which includes self-leveling sealant for use in cracks in horizontal surfaces and anti-sag sealant for fixing cracks in vertical surfaces without sagging or sagging. You can cut them into the slab with a circular saw equipped with a blade on the day after pouring them.

Wetting the concrete and covering it with plastic or a tarp to reduce evaporation works well but you will have to re-wet the slab daily which could damage the surface by peeling off and replacing the cover.