How much cracking in slab is normal?

If the crack is larger or larger (an “active crack”), or if one side of the crack is higher than the other, you may need a structural engineer to review the work. Concrete cracks may seem scary at first, but they are common in almost every home that has a concrete floor. If someone tells you that your concrete floor shouldn't have any cracks, be careful, you don't know what you're talking about. Cracks that crack 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, cracked cracks are not a structural concern. All questions will be considered for use in “Ask the Inspector”, but cannot be answered individually. If those clues of the actual foundation settlement and foundation movement are absent, you are more likely to see settlement on the concrete slab itself.

We used the three Carson Dunlop Associates sketches shown here to comment on the occurrence, causes, and importance of cracking and movement in the construction of poured concrete slabs. Although there are many reasons for concrete slabs to crack, most do not lead to serious structural or foundation problems; however, there are times when cracks are a warning sign of basic or other problems. If these sublayers are not well compacted, when concrete is poured onto them, the heavy weight of the concrete will cause these areas to sag a little, and then cracks can occur. Since concrete will always move just a hair from warm to cold seasons, those cracks can wreak havoc on tiles, causing joints or even the tiles themselves to crack.

Each type of concrete foundation, wall, basement slab, floor slab, or crack slab is analyzed and described with the photographs below. But the edges of the floor slab rest on an edge integrated into the poured concrete base that also supports the walls of the building. Steel reinforcement for rebar is probably the most common form of reinforcement used in concrete slabs for the past 40 to 50 years. These control joints are designed to weaken concrete in certain areas, so that concrete cracks in a straight line in these spaces.

If you see a pattern of cracks or rust on the garage floor that looks like the cracks are 12 to 24 inches apart and run in one or two directions, it may be an indication that the rebar was placed a little too high and you don't have enough concrete to cover it properly. After heavy rain or snow melt when the ground below is soft and damp, excessive weight on the slab can press the concrete down and cause cracking. One of the most common mistakes people make when looking at their garage floor is confusing a cold joint with concrete that has actually cracked. Crusting cracking generally occurs during the concrete stamping process, which is a way of adding texture or pattern to concrete surfaces.

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