Shrinkage cracks are a common occurrence in cast-in-place concrete walls, and they are usually nothing to worry about. These thin, shallow cracks are usually only on the surface and should disappear within a month. Although they are mostly cosmetic, it is important to understand the causes of these cracks and how to prevent them. When analyzing the causes of cracking within a concrete masonry wall, it is important to understand all of the mechanisms associated with cracking of concrete masonry.
Shrinkage in concrete masonry varies, but there are shrinkage coefficients published in ACI 530-11 (American Concrete Institute). Poor preparation of concrete foundations and inadequate steel reinforcement when pouring the concrete can lead to more significant vertical cracks. A typical concrete block has a compressive strength of approximately 2000 psi, as do most common mortars. Fine cracking within concrete block walls as a result of concrete masonry shrinkage is an expected fact.
If your concrete is a little older, a concrete repair professional can help you fix the cracks. ACI 116R-90, Cement and Concrete Terminology, defines fine cracks as cracks in an exposed concrete surface that have widths so small that they can barely be perceived. When pouring a new concrete base, it is important to mix the concrete properly and pour it slowly. To ensure even curing, cover the concrete with an insulating plastic sheet or even straw to trap moisture.
Concrete additives and curing compounds can also help the concrete cure faster and resist cold temperatures. After the concrete has fully cured, you can also consider using a concrete sealing compound to improve appearance and reduce cracking.