Cracks in concrete are a common occurrence, and they develop when the stresses in the concrete exceed its strength. This can be caused by normal shrinkage as the concrete hardens and dries, or by excessive weight placed on the concrete slab. Cracks can appear on floors, entrances, walkways, structural beams and walls. Although cracking cannot be prevented, it can be significantly reduced or controlled by understanding the causes and taking preventive measures.
Most cracks should not be a cause for alarm, as shrinkage cracks are very common in cast-in-place concrete walls. These cracks are thin and shallow, and usually don't run continuously or in a straight line. The strength of concrete is measured in pounds per square inch (PSI). Placing too much weight on a concrete slab can cause cracking.
When you hear that a concrete mix has a strength of 2000, 3000, 4000, or more than 5000 PSI, it refers to the amount of pressure needed to crush that concrete slab. Since concrete cannot shrink around a corner, stress will cause the concrete to crack from the point of that corner. Proper site preparation, quality mixing and good concrete finishing practices can help minimize the occurrence of cracks and produce a more aesthetically pleasing result. Crust cracking generally occurs during the concrete stamping process, which is a way of adding texture or pattern to concrete surfaces.
If cracks appear soon after pouring the concrete base, it may have been mixed poorly or poured too quickly. After the concrete has fully cured, you may consider using a concrete sealing compound to improve appearance and reduce cracking. Concrete poured when the temperature is cold will have fewer shrinkage cracks than when it is hot; and in general, the more water added when mixed for the first time, the more shrinkage cracks there will be. Precast concrete walls are built off-site and then trucked to the construction site for placement. To help prevent cracking during curing, cover the concrete with an insulating plastic sheet or even straw to trap moisture and help it cure at an even rate. A cold joint is where a batch of concrete is poured and it has started to set or has hardened and then another batch of concrete is poured against the previous batch. If your concrete is a little older, a professional can help you fix the cracks.
A more massive vertical crack can occur when construction contractors improperly prepare concrete foundations and when there was poor steel reinforcement when workers poured concrete for the wall. In addition to traditional curing methods, additives and curing compounds can help concrete cure faster and resist cold weather. It takes about a month for new concrete to settle by full. A reputable local professional will know how to keep a concrete slab in good condition for optimal curing.