We all have seen concrete floors and walls with smooth, flawless surfaces. Yet cracks are not uncommon. When a crack shows itself in especially impressive structures, laymen tend to say something derogatory about the builder. The fact is, some cracking is acceptable. It really is. The American Society of Concrete Contractors even issued a position paper on the subject in 2010.
This is the opening passage: “Some concrete professionals believe that reinforced concrete structures should not crack. With that firm belief, when cracking does occur, they often claim that the concrete contractor caused the cracks and should pay for repair. Cracks in reinforced concrete, however, are not a defect but are specifically included as part of the design process.”
The paper goes on to say that “when high-strength reinforcing steels are used at high service load stresses, visible cracks should be expected.” It then talks about “reasonable crack width.” Presumably, anything too wide is a defect. The American Concrete Institute specifically says that a deep crack that is wider than a credit card “could be a sign of more serious problems.” It might indicate a foundation is settling.
The ACI, is more accepting, however, of non-structural cracks — the cosmetic hairlines that sometimes mar a surface. If a hairline crack isn’t widening, isn’t apt to develop into a crack that will cause someone to trip, and doesn’t collect dirt and other unsanitary materials, the institute’s general suggestion is just to live with it. Or if a crack is too ugly to ignore or otherwise is distracting, covering it with a slurry mix is recommended.
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