In general, cracks in the floor are nothing to worry about. The only time you may worry is if the cracks start to change vertically, which suggests that there is some settling. Cracks in the floor of a concrete garage may indicate that there are problems with the foundation or other problems. As buyers or homeowners, we want to know how to know if these cracks are serious or, basically, when to worry.
Cracks caused by drying shrinkage and thermal shrinkage will be active cracks at first, but may eventually stabilize and become latent. A key factor is whether these are new cracks that are increasing in size or stable cracks that have been there for years and are likely to not increase in length or width. Unless the structural tolerance level is exceeded, early cracking formed by early thermal shrinkage is not considered to affect the overall safety of concrete structures. However, a qualified and licensed professional should be consulted to classify the severity of the crack and properly investigate the cause of the crack and determine the most effective method of repair if necessary.
Concrete cracks when subjected to tensile stresses (forces that separate something versus forces that push something). In soils with a clay content, especially a high clay content, the pressures of rising or lifting the soils can crack the foundation. The American Concrete Institute addresses the issue of concrete cracking in its manual from the American Concrete Institute, ACI 302.Cracking in category 3, i.e. cracking between 5 and 15 millimeters, requires evaluation, but is considered useful (minor repair).
Certain concrete cracks can best be repaired by targeted injection of appropriate material adapted to the diagnosis of the individual crack, followed by a suitable protective concrete coating. This expansion process can take 5 to 20 years before cracking eventually leads to the failure of the concrete structure. I guess the structure of the building has been applying pressure to the slab for so many years that it cracked over time. Foundations that are not properly sized and engineered for the type of soil and the loads that the foundations bear will create cracks.
While early cracks may initially be considered as a minor deficiency, it is recommended that building owners and building maintenance managers appoint qualified repair contractors to properly repair these cracks sooner rather than later to help extend the life of the concrete structures. Poor drainage near the foundation of a house is actually one of the most common causes of cracks and foundation damage. When the floor of a garage has a significant number of cracks or are wide cracks or when a crack has one side substantially higher than the other side; it would be wise to examine these cracks more thoroughly and check the house for other signs of possible soil and foundation movement.