Types of Cracks in Concrete

Tremendous forces can build up inside the wall due to any causes of cracks. When the forces exceed the strength of the concrete, cracks will develop. Each of these causes leaves a "signature" typically in the type of crack it creates. The majority of these cracks are of little concern by themselves.

Shrinkage crack in concrete wall

Shrinkage

Shrinkage cracks in a poured concrete foundation can be diagonal or vertical and are usually uniform in width. Sometimes these cracks have a V-shape (less frequent), with the top of the crack looking larger and the crack getting smaller as it travels towards to floor and diminishing or stopping before reaching the bottom of the foundation wall. If the crack reaches the bottom, the crack might damage the building's footings, and the crack might have a significant impact on the foundation structure.

Shrinkage cracks should not be ongoing nor of structural significance, though they may invite water entry through the wall. In poured concrete foundations, shrinkage cracks are usually due to conditions at original construction: poor concrete mix, rapid curing or possibly other states. In any case, concrete shrinkage causes the concrete to develop internal stresses. Unless control joints were included in the wall or floor slab design, these stresses would cause the wall or floor is likely to crack in a classic "concrete shrinkage pattern" as the concrete cures.

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Hairline crack in concrete wall

Hairline

Hairline cracks may develop in concrete foundations as the concrete cures. Hairline cracks do not cause problems with the stability of the foundation but do cause leakage problems. If the cracks appear shortly after pouring the concrete foundation, concrete may have been mixed poorly or poured too quickly. In poured concrete foundations, hairline crack frequently appear in the center of the walls because the wall corners have greater stability.

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Settlement crack in concrete wall

Settlement

Settlement cracks may appear when the underlying ground has not been compacted or appropriately prepared or if the subsoil was not of the proper consistency. A settlement crack may also appear as a random crack above areas where the soil of the subgrade was uneven after the concrete was poured. Settlement cracks are usually more extensive at the top of the crack than the bottom as the foundation "bends" over a single point, allowing differential settlement. This type of crack is usually continuous and may occur multiple times in a wall.

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Temperature crack in concrete wall

Temperature and Shrinkage

Horizontal cracks found in the center of the wall are most likely caused by an applied load such as backfill around foundation compacted improperly or too soon, earth compacting as it settles, hydrostatic pressure against foundation due to high water table and poor drainage against the foundation wall, or heavy equipment operated too soon or too close to the foundation wall. Horizontal cracks found high up on the wall are most likely caused by frost damage. Sometimes these fine cracks are not noticed for years. In a case like this, a structural engineer should be consulted.

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Vertical crack in concrete wall

Vertical

Vertical cracks often appear in multiples (multiple cracks in one or more area). Vertical foundation cracks in poured concrete foundations that tend to appear nearly straight or wandering, generally even in width, intermittent, or more often straight is caused by shrinkage/thermal and are usually low risk. If there is significant vertical dislocation or signs of ongoing movement, you should consult a structural engineer. If the cause is shrinkage, it is probably less of a concern than if due to settlement.

A vertical foundation crack due to earth loading or frost would be unusual. A more massive vertical crack can occur when the construction contractors incorrectly prepare the concrete footings and when the wall had poor steel reinforcement as the workers poured the concrete for the wall. Cracks can also occur during the footing settlement.

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Diagonal crack in concrete wall

Diagonal

Settlement usually causes diagonal cracks that are almost the full height of the foundation wall. When there's a settlement problem with footing on one side of the wall, this settlement can also cause a diagonal crack. In a case like this, a structural engineer should be consulted. If the diagonal crack is wider at the top than at the bottom, then it may be caused by expansion clay soil or frost damage. If the crack is wider at the bottom than the top, there is likely a problem with the settlement beneath.

Some uniform diagonal cracks are merely caused by shrinkage and will only cause water leakage problems. Diagonal cracks that emanate from a corner of a window and other openings are called reentrant cracks and are usually the result of stress built-up at the corner.

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Horizontal crack in concrete wall

Horizontal

Horizontal cracks found in the center of the wall are most likely caused by an applied load such as backfill around foundation compacted improperly or too soon, earth compacting as it settles, hydrostatic pressure against foundation due to high water table and poor drainage against the foundation wall, or heavy equipment operated too soon or too close to the foundation wall. Horizontal cracks found high up on the wall are most likely caused by frost damage. Sometimes these fine cracks are not noticed for years. In a case like this, a structural engineer should be consulted.

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Structural crack in concrete wall

Structural

Structural cracks in residential foundations usually result from horizontal loading or settlement. Most (but not all) structural cracks resulting from an applied load (hydrostatic pressure or heavy equipment around foundation wall) are nearly horizontal and appear 16" to 48" from the top of the wall. They are more common in block foundation walls.

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Floor crack in concrete

Floor

Floor cracks in concrete slabs are relatively common and usually not worrisome on a structural level. They should be repaired to prevent common issues like moisture, insects, and damage from seeping through. When floor cracks leak, it is usually caused by hydrostatic pressure or a high water table. Therefore, sealing the crack will redirect those issues elsewhere, so fixing the source of those problems beforehand is recommended.

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