Cracks in concrete are very common and occur for various reasons. Rest assured that even with the best floor design and proper construction, cracks in concrete are very common and, in some situations, unavoidable. Fortunately, they can usually be repaired. Fine cracks are commonly observed in newly laid concrete and their appearance is due to the phenomenon of plastic shrinkage.
As the name implies, these cracks are very small, about 0.003 inches (0.08 mm) wide and can be very shallow. Cracked cracks are very fine surface cracks that resemble cobwebs or broken glass. When the top of a concrete slab loses moisture too quickly, cracks are likely to appear. While unsightly, cracking cracks are not a structural problem.
Cracks in concrete are extremely common, but they are often misunderstood. When a homeowner sees a crack in his slab or wall, especially if the concrete is relatively new, he automatically assumes something is wrong. It's not always like that. Some types of cracks are inevitable.
The best thing a contractor can do is try to control cracking. This is done by properly preparing the subbase, making sure that the concrete is not too wet, using reinforcement where necessary, and correctly placing and spacing the crack control joints and expansion joints. However, cracks sometimes occur despite the precautions taken. Fine cracks usually develop within the first month and most foundation cracks appear within the first year.
In order to be able to pour and work it, almost all concrete contains more water than is needed for the hydration of the cement. If you see cracks or curls, it is possible that the concrete will dry out faster than it should during pouring. Diagonal cracks emanating from a corner of a window and other openings are known as re-entrant cracks and are usually the result of stress buildup in the corner. Fine cracks do not cause problems with the stability of this base, but they do cause leakage problems.
Such cracks can appear up to a year after the basement floor is poured, depending on how quickly the slab dries and the humidity of the basement. If you see several cracks, cracks wider than the hairline, or cracks are widespread throughout the house, this may indicate that your base is settling. This category covers the performance of concrete whose shape can no longer be altered without damage. It includes cracks caused by drying shrinkage, as well as those resulting from temperature movements that occur in all materials exposed to the elements.
Concrete contractors often use control joints to control where cracks will occur when they cannot avoid them. When the seal is embedded, it separates the surface near the stamped joints and causes small cracks around the outer edges of the “stones”. Other cracks that occur after hardening can be caused by the lack of proper reinforcement in the corners, insufficient depth of concrete over the bends in the reinforcement, the nesting of reinforcing steel in concrete, the lack of expansion and contraction joints. In most cases when cracks appear in concrete, the crack can be identified and the cause of cracking established.
Whenever there is a settling problem with the foot on one side of the wall, this settlement can also cause a diagonal crack. Cracking cracks after hardening can result from excessive flotation that tends to attract water and cement to the surface, which then comprises weak concrete subject to high shrinkage stresses. Such cracks occur when the concrete near the surface takes a partial setting, while the rest of the concrete can still settle. Along with these traditional curing methods, concrete additives and curing compounds can help concrete cure faster and resist the weather.