Dictionary of types of foundation cracks, movement, damage:
Guide to identifying & evaluating different types of concrete or masonry foundation, wall or floor cracks in buildings: this article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.
Foundation cracks and movement are discussed by type and location of foundation cracks, vertical foundation cracks, horizontal cracks, and diagonal foundation cracks, and shrinkage cracking.
To be used properly, this information must be combined with specific on-site observations at the particular building in order to form a reliable opinion about the condition of that building's foundation. Anyone having concern regarding the structural stability, safety, or damage of a building, foundation or other components, should consult a qualified expert.
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Foundation cracks, which are signs of foundation damage, can mean very different things depending on the material from which a foundation is made, the location, size, and shape of the foundation crack, and other site observations.
The size, shape, pattern, location of foundation cracks on a building, along with correlation with other site and construction conditions helps distinguish among probable causes.
To understand the cause, effect, and remedy for all types of building foundation or masonry wall damage or movement we have categorized foundation damage assessment and repair into these broad categories:
This foundation crack diagnosis and repair article series discusses in detail the process of evaluating foundation cracks and signs of foundation damage by examining the crack size, shape, pattern, and location.
By knowing the probable cause and history of foundation cracking or movement one can distinguish between continuing movement (more likely to be a problem) and single events which may, depending on extent of damage, not require repair. This chapter elaborates types and patterns of foundation cracks to assist in that evaluation.
Look at shape, pattern, frequency of occurrence, relationship to wall discontinuities and angles, placement of wall penetrations, correlation with cracks in floors, and location in the wall (corners, center), as well as length, width, continuity, age of wall, relation to site conditions (depth of backfill, blasting, rock).
Shrinkage cracks are usually uniform in width or (less common) vee-shaped, wider at top and diminishing or stopping before reaching the bottom of the foundation wall (where attachment to footing may tend to hold foundation wall materials in place). A wall crack which continues into the floor is likely to involve the building footings and may be a settlement crack of more structural importance.
Concrete shrinks as it cures. In poured concrete, shrinkage cracks may be non-uniform if wall components are held by footings/framing; very often there are minor shrinkage cracks which are hairline, random, intermittent, multiple, and meandering in the concrete, forming discontinuous cracks in the wall.
Shrinkage cracks occur as concrete cures, appearing more frequently and larger if the mix was improper and where control joints were omitted. Omission or pattern of placement of steel reinforcement may also be a factor in crack formation and location.
Poured concrete shrinkage cracks: usually shrinkage cracking is due to conditions at original construction: poor mix, rapid curing, possibly other conditions. Shrinkage cracks are less likely to require structural monitoring and repair in poured concrete as they would be expected to continue after initial curing.
Concrete block foundation walls shrink as they cure. They rarely expand much on exposure to moisture and temperature variations. In concrete block walls shrinkage cracks are likely to be uniform in width and usually occur towards the center of a concrete masonry unit (CMU) wall. The wall is stronger at the building corners.
Brick walls do not normally shrink, but rather, grow indefinitely. Bricks are not often used for below-grade foundations but were often used above-grade supporting the first floor of older buildings, and of course entire buildings may be constructed using structural brick walls (look for the bond courses).
If you see a crack in a brick wall it's more likely due to movement in the structure, a support problem, or due to thermal expansion.
Watch out: Cracks in structural brick walls may be very serious if the bond courses are broken as there is then a risk of sudden catastrophic wall collapse. Cracks and especially bulged cracked brick walls need immediate expert investigation.
Stone foundation walls do not normally crack through individual stones, but the interlaced stone layout of the wall may be bulged and cracked due to damage from frost, loading from driving vehicles near the wall, or by the removal of stones to pass piping or make doorways.
As with other cases of foundation movement, a diagnosis of the cause, amount of movement, and effects on structure are needed to decide what repair may be needed.
In the photos shown here, substantive cracks appeared and continued to increase in size in this poured concrete foundation used to support a modular home which had recently been completed. The cracks and foundation movement were probably due to a combination of: poorly prepared foundation footings, blasting on an adjacent building lot to prepare that site for new construction, and possibly omission of steel reinforcement in the poured wall.
The cracks in this building foundation wall were visible shortly after construction as vertical hairline openings (less than 1/16" wide) in the right hand foundation wall, above grade and inside in the basement. Within a year the owner reported several times that the cracks were becoming noticeably wider.
A careful inspection of the building interior suggested that the front foundation wall and portions of the right foundation wall were settling. There were no corresponding cracks in the finished surfaces of the structure, probably because this was very stiffly-framed modular construction. Notwithstanding the absence of damage upstairs, this was a problem that deserved further evaluation and repairs.
The builder may have repaired the foundation by supporting it from below using one of the methods described at FOUNDATION REPAIR METHODS.
This settlement crack probably occurred during initial footing settlement. Notice that it is wider at the top than the bottom of the crack.
This suggests that the footing to the left or right of the crack has moved downwards, with further downwards movement as we move further from the crack itself.
If this is new construction and the crack does not change in width the site conditions may have stabilized.
Additional photographs of types of foundation cracks and other foundation damage: we have an extensive library of photographs which will be added to this document. Pending completion of that work, contact the author if assistance is required with images.
Note: vertical foundation cracks often appear in multiples multiple cracks in one or more area.
While a vertical foundation crack could be serious depending on its cause and on the type of foundation in which it appears (stone, brick, masonry block, concrete), these are often the least threat to the building. If there is significant vertical dislocation or signs of ongoing movement, further investigation is more urgent. If the cause is shrinkage (concrete, masonry block) it is probably less of a concern than if due to settlement. A vertical crack due to earth loading or frost would be unusual.
Details about the causes & repair methods for vertical cracks in building foundations & walls are at VERTICAL FOUNDATION CRACKS
This settlement crack probably occurred during initial footing settlement. Notice that it is wider at the top than the bottom of the crack. This suggests that the footing to the left or right of the crack has moved downwards, with further downwards movement as we move further from the crack itself. If this is new construction and the crack does not change in width the site conditions may have stabilized.
Clues to help diagnose the probable cause of diagonal foundation cracks in buildings:
Note that often at these foundation failures cracks are visible both outside and inside, but outside they may be covered by backfill.
For detecting evidence of sink holes in an area by visual inspection
see Sink Holes: Can X-Ray Vision [Advanced Building & Building Site Inspection Techniques] Warn of Sink Holes? in Florida or elsewhere
Details about the causes & repair methods for diagonal cracks in building foundations & walls are
at DIAGONAL FOUNDATION CRACKS
These notes presume that you are examining a wall which is entirely or nearly all below-grade level.
Horizontal foundation cracks located in the upper third of a concrete block wall (presuming most of the wall is below grade) are most likely to have been caused by vehicle loading or in freezing climates, by surface and subsurface water combined with frost. In northern climates if we see cracked mortar joints in the top third of a block wall, at about the same depth as the frost line in that area the damage is almost certainly due to frost.
Often outside we'll find corroborating evidence such as drip lines below the building eaves confirming a history of roof spillage against the building, and back inside we may see that the foundation damage is occurring only at the building walls below roof eaves and not at the gable ends of the home.
Masonry block or stone walls which are cracked and/or bulging inwards at mid height on the wall are likely to have been damaged by vehicle traffic or earth loading.
The forces exerted by soils against a foundation wall increase geometrically as we move from surface level of the soil against the wall to the areas near the bottom of the wall. In other words, earth pressure is greatest at the bottom of the wall. This fact helps us distinguish between frost or water-related cracking and simple earth loading in some cases since a wall which has become dislocated laterally only at or near its bottom is likely to have been damaged by earth loading.
Construction methods for attached garages (as opposed to a garage located under a home and adjoining its basement) may create some special opportunities for foundation cracks:
Horizontal foundation cracks are usually visible only from inside a basement or crawl area unless building is all masonry.
Lateral or horizontal movement of a masonry foundation wall inwards from earth pressure will often be seen at the first mortar joint above a basement or crawl space slab. Remember that the slab itself may be holding the very first course of masonry blocks or brick in place. This is a useful detail to keep in mind if you are using a plumb line and measuring tape to document the total amount and location of wall movement.
The bottom course of concrete blocks or bricks, held in place by the floor slab, can usually be taken as a baseline of zero movement, from which other measurements to the plumb line are compared over the height of the wall.
Details about the causes & repair methods for horizontal cracks in building foundations & walls are at
Cracks will occur in masonry structures: Most solid materials may both expand and contract in response to temperature variations. Solid materials may be cracked by pressure from loading. In masonry foundations, bricks actually expand indefinitely, though probably at a decreasing rate. Poured concrete shrinks after pouring. Masonry blocks may shrink and expand. All of these materials respond to changes in moisture and temperature.
A long brick wall exposed to sunlight and cold weather and built without expansion joints will crack and fail. Concrete block walls shrink but don't normally expand (below grade). Poured concrete shrinks during curing but may also expand or contract in response to moisture.
Determining when action is needed: All cracks need to be separated into those which are expected to require no further repair except possibly cosmetic (which can help future monitoring), those which merit ongoing monitoring for change and possibly signs of worsening conditions, and those which are so significant as to require repair.
Setting priority of action: Repair work needs to be identified with respect to urgency, ranging from immediate (risk of collapse or other unsafe conditions) and less urgent.
To the extent that the inspector can see the extent of movement and the potential for damage to a building, and to the extent that the inspector can make a reasonably confident guess about the cause of foundation damage or movement, s/he can estimate the chances of its continuance and thus help set a priority for further evaluation or repair, as well as setting the specifics of outside repairs to reduce further damage such as keeping water or vehicles away from the building.
Details about how we distinguish among cracks caused by foundation or masonry wall shrinkage, expansion, or settlement in building foundations & walls are
at SHRINKAGE vs EXPANSION vs SETTLEMENT - below we continue with examples of each of these movement patterns.
A variety of site conditions can lead to cracks in a concrete or other masonry foundation walls or floor slabs.
Speaking generally, foundations may be damaged and cracks may appear from innocent causes unlikely to affect the structure such as concrete shrinkage cracks, initial settlement, or from potentially more serious causes such as ongoing settlement, unusual pressures or loading, or from improper construction.
Shrinkage cracks in poured concrete are easily recognizable and can be distinguished from other types of cracks that occur later in the life of a foundation wall or floor slab.
Concrete shrinks as a natural process during its curing. You can see the shrinkage of even a perfect concrete floor slab with no visible cracks in its surface if it was poured inside of an existing foundation. Notice the gap between the edges of the slab and the foundation wall? Notice the stains or concrete debris on the wall at the slab level? These indicate that at the time the slab was poured it was touching the wall. A poured concrete wall shrinks as well.
Concrete curing is a chemical reaction, not just "drying" or loss of water. But depending on the concrete mix, amount of water, portland, aggregate type, temperatures, humidity, groundwater, sun exposure, groundwater, and other conditions, the amount of shrinkage that will occur in concrete as it cures varies.
In any case, this concrete shrinkage process causes the concrete to develop internal stresses. To relieve those stresses, unless control joints were included in the wall or floor slab design, the wall or floor is likely to crack in a classic "concrete shrinkage pattern" as the concrete cures.
Cracks in a poured concrete foundation which are diagonal or vertical and which are generally uniform in width, or which taper to an irregular hairline form and stop entirely, which are usually discontinuous in the crack's finest or hairline area (the crack "stops and starts" in the same area), are usually shrinkage cracks and should not be ongoing nor of structural significance, though they may invite water entry through the wall. [See our article on Using Polyurethane Foam for Foundation Repairs]
Shrinkage cracks in concrete range in length from a few inches to the entire height of the concrete wall, extending from wall top to bottom. Concrete shrinkage cracks virtually always extend through the full thickness of the foundation wall, which means they can provide a ready path for water entry into the building.
Common areas for a shrinkage concrete crack to develop are under a basement window, above a doorway in the middle of a long wall or where the foundation "steps down." Shrinkage cracks also often occur near the middle of a large poured concrete wall [or floor] if no control joints were used. [Concrete control joints are very often omitted in residential construction.
Shrinkage cracks and how to recognize and diagnose them are discussed further at SHRINKAGE vs EXPANSION vs SETTLEMENT.
Before repairing a foundation crack by sealing it against water entry, it is important to diagnose the cause of the crack and its effects on the building structure.
When it has been determined that there is an underlying ongoing problem such as one leading to foundation movement or damage to the structure, the underlying problem should be corrected as part of any foundation or slab repair.
Cracks in poured concrete walls that are larger than 1/4", cracks which are increasing in size, or cracks which
are otherwise indicative of foundation movement should be evaluated by a professional.
The diagnosis and evaluation of foundation cracks and structural
foundation damage and repair methods are discussed
at FOUNDATION REPAIR METHODS
Once any concrete cracks it is possible for water to leak into the building through the crack. There are several ways to repair a basement crack leak. An easy, quick, and effective measure to stop basement or crawl space water entry through a foundation crack is to perform an injection of polyurethane foam into the basement crack. [Also be sure to find and fix the sources of water outside.]
Water entry leaks at foundation cracks: Polyurethane foam sealant is used for foundation crack repairs to stop water entry.
(Also find and correct outside water sources). See our article
on Using Polyurethane Foam for Foundation Repairs.
Structural repairs as well as sealing against water entry may be attempted for cracked foundations using masonry epoxy products. These products may be used for repairing cracks in concrete foundations, possibly including structural repairs, following evaluation and advice from a foundation professional. An evaluation of the presence, absence, or condition of reinforcing steel in cracked concrete foundations should be a part of the inspection.
See our discussion of foundation repair methods
at FOUNDATION REPAIR METHODS
Details about how we distinguish among cracks caused by foundation or masonry wall shrinkage, expansion, or settlement in building foundations & walls are
at SHRINKAGE vs EXPANSION vs SETTLEMENT
Non-shrinkage cracks in concrete: The photograph shows a settlement crack in a garage floor concrete slab. This particular crack, occurring near the garage entry, may have been caused by frost since this is a New York home. (It's colder at the garage doors than further inside the building and there may be more water under the slab close to the building perimeter.)
But a very common cause of settlement cracks in slabs (and some walls) is poor site preparation, such as pouring the slab (or footings) on soft fill.
As an example of a concrete crack that occurred later in the life of a structure (thus is not due to initial curing shrinkage) and to understand why such a non-shrinkage crack would look different from a shrinkage crack, imagine Superman breaking a piece of cured, hard, dry, solid concrete slab by bending it.
The crack that would appear in cured concrete would not be intermittent along its length, it would be continuous even if it is not a straight line. Depending on the cause of such a later-in-life concrete crack, it might also be wider at the top than at the bottom (foundation footing settlement) or there might be horizontal dislocation (one side of the crack sticks into the building further than the other, or one side of the floor slab crack sticks up more than the other).
Settlement around a Lally column pier may have produced the cracks visible in the slab around the Lally column in this photograph. A hypothesis is that the pier below the column was functioning properly but the slab was poured on loose fill around the rest of the basement floor.
The slab settled away from the pier but where the pier supported a portion of the slab that was poured over it, the pier prevented settlement of that area. Observing that the high-side of these cracks was the side closer to the Lally column supports this view.
Brick, in particular, whether used in a foundation or as a building wall, expands over time and as moisture, temperature, and other conditions vary. Dave Wickersheimer, P.E. and R.A., who is a masonry failures expert from the SHC, informs us that brick "grows" or expands indefinitely. However if we exclude heating effects of sun exposure (discussed below), most brick expansion from its internal chemistry probably occurs early in its life.
Thermal expansion of brick: Brick walls exposed above-grade are subject to significant heating gains from sunlight and may expand and contract sufficient to cause major damage if proper control joints are not used during construction. If you observe long expanses of brick masonry walls above grade and without expansion joints, look for expansion cracking.
When caused by thermal expansion, brick walls may show most movement at the two ends of the wall most-exposed to sunlight. The author, using a simple plumb line and measuring tape, has measured as much as 4" of expansion found at the top of a brick structure whose wall corners leaned out 4" over the wall bottom from this force. [Note: POK JCC file-DJF].
Brick walls below-grade are of course not exposed to heating and expansion from sunlight, but instead are exposed to earth pressure (look for horizontal cracking), and in freezing climates frost damage (look for horizontal cracks in walls at or near the frost line, and look for stair-stepped cracks at corners of the building.
Brick cracking due to thermal expansion is discussed and illustrated in detail at THERMAL EXPANSION CRACKS in BRICK
Defects in concrete mix (too much water, for example), or defects in placement of steel or iron reinforcement (too close to surface, for example), as well as use of problem materials in concrete such as high levels of cinders, coal ash, or Iron sulfide mineral (pyrrhotite) can cause horizontal, vertical, or varied-pattern or "wandering" cracks in masonry foundations.
See FOUNDATION DAMAGE by MATERIAL or INCLUSIONS for details.
A settlement crack is more likely to be wider at top than its bottom as the foundation "bends" over a single point, allowing differential settlement; it is possible for a settlement crack to appear fairly uniform however if a foundation breaks vertically and then pursues differential settlement.
Settlement cracks need to be separated into initial settlement due to construction or site factors and ongoing settlement due to site factors.
Usually settlement cracks are wider at the top of the crack than at the bottom, are usually continuous, and may be multiple!
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Or see FOUNDATION DAMAGE SEVERITY
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Questions & answers about types of foundation cracks & damage, posted originally in this article are now found at FOUNDATION CRACK DEFINITIONS FAQs
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