Poured concrete foundation
Cast concrete can develop cracks from drying shrinkage, thermal movement, restraint, settlement, loading and other causes. Cracks may pass directly through the concrete rather than following a joint pattern.
Foundation Crack Guide
Concrete and Block Foundation Cracks: What Different Crack Patterns Can Mean
Foundation cracks are common enough that the presence of a crack alone does not tell you whether a foundation is failing. The more useful clues are the crack pattern, whether one side has moved relative to the other, whether the wall is bowing or leaning, where the crack is located and whether the condition is changing.
Poured concrete and concrete block walls also crack differently. A vertical crack through a concrete wall is not interpreted the same way as a stair-step crack following mortar joints in block masonry, and a horizontal crack through a below-grade block wall deserves different attention again.
Movement matters more than a universal crack-width number. A fine crack with no displacement can be very different from a wall where courses are shifting, bowing inward or moving out of plane.
A crack pattern can suggest where to investigate. It does not, by itself, prove the cause.When Is It More Concerning?
First Distinction
Is the wall poured concrete or concrete block?
The material changes how cracks tend to form and how movement becomes visible.
Concrete block foundation
Concrete masonry has regular bed and head joints, so movement often becomes visible along the mortar joints. Stair-step, horizontal and vertical joint cracking can each point toward different movement patterns.
Mixed or altered foundation
Older homes may contain additions, repaired sections, block built against concrete, reinforced patches or new openings. Cracks near those transitions can reflect the way different materials and support conditions move relative to one another.
Crack Patterns
What can different foundation crack patterns suggest?
Pattern recognition helps narrow the investigation, but displacement and building context still matter.
Vertical crack in poured concrete
Vertical or near-vertical cracks are commonly associated with concrete shrinkage or restrained movement, especially when they are relatively straight and show little displacement. Settlement or loading can also create vertical or diagonal cracks, so orientation alone is not enough to diagnose the cause.
Horizontal crack in block
A horizontal crack in a below-grade concrete block wall can indicate that the wall is bending inward under lateral pressure. The concern increases if the wall is also bowed, displaced or losing alignment.
Stair-step crack in block
Stair-step cracks follow the mortar joints and can occur where part of the wall or footing moves differently from the rest. The Concrete Masonry & Hardscapes Association specifically identifies differential settlement as a typical cause of stair-step cracking in concrete masonry.
Diagonal crack
Diagonal cracking can form where stresses concentrate, including near corners, openings or areas of differential movement. It should be interpreted with the surrounding wall, footing and framing conditions.
Crack with offset
If one side of a crack projects inward, outward or vertically relative to the other, the wall has moved in more than just a cosmetic way. Displacement is often more important than the crack width itself.
Several crack patterns together
Horizontal cracking, stair-step cracking, bowing and movement around openings occurring together can indicate a broader foundation or support problem rather than one isolated mortar or shrinkage crack.
Vertical Cracks
When is a vertical crack more likely to be shrinkage, and when does it deserve a closer look?
Concrete loses moisture as it cures and dries, and shrinkage is one reason cracks can develop in cast walls. The American Concrete Institute notes that cracking is possible in concrete foundation walls and that visible cracks can be influenced by shrinkage and other time-dependent effects.
A relatively straight vertical crack with little or no displacement can therefore be very different from a vertical or diagonal crack accompanied by settlement, rotation, movement at the sill, doors that change position or a footing problem.
This is why one fixed crack-width rule is not a reliable homeowner diagnostic tool. The same visible width can occur in two walls with very different causes, reinforcement, loading and movement histories.
More Useful Questions
Look beyond the width.
✓Is one side of the crack offset from the other?
✓Has the crack changed over time?
✓Does it continue into the footing, floor or wall above?
✓Are nearby openings or framing also moving?
✓Is water entering through it?
Water and structure are separate questions. A wall can leak without being structurally unstable, and a structurally significant crack can exist without obvious water entry.
Horizontal Cracks & Bowing
Why is a horizontal crack in a below-grade block wall taken more seriously?
Below grade, the soil outside the foundation pushes laterally against the wall. The National Research Council's Illustrated User's Guide explains that foundation walls resist earth pressure and that top support, wall height, backfill and surcharge loads all influence the forces on the wall.
If a block foundation begins bending inward, a horizontal crack can develop along a bed joint near the area of greatest movement. The wall may also bow, with the centre moving farther inward than the top or bottom.
Repointing that joint does not restore the wall's structural capacity or remove the pressure causing the movement. Where a horizontal crack is accompanied by bowing, displacement or progressive movement, structural assessment should come before cosmetic repair.
Stair-Step Cracks
Why do cracks step through the mortar joints in a block foundation?
Differential settlement
If one portion of the footing or supporting soil moves more than another, the block wall may crack diagonally through the weaker mortar joints. CMHA identifies differential settlement as a typical cause of stair-step cracking in concrete masonry.
Movement near openings
Windows, doors and beam pockets interrupt the wall and can concentrate stress. Cracking that starts from an opening should be considered together with support, lintels, framing and footing conditions.
Foundation or soil change
Additions, disturbed soil, drainage changes, frost effects or different footing conditions can create movement where one part of a building responds differently from another.
More Concerning Conditions
What makes a foundation crack more than a routine repair question?
Wall bowing or leaning
A wall that is visibly out of plane has moved as an assembly. That deserves more attention than a fine isolated crack with no displacement.
Increasing displacement
A crack or wall that is clearly changing over time suggests active movement and is more important than an old stable crack whose position has remained unchanged.
Loss of support
Voids beneath a footing, undermining, major soil movement or deteriorated bearing conditions can affect the foundation's ability to support the building.
Several symptoms together
Foundation cracking accompanied by floor movement, framing changes, sticking doors, shifted openings or exterior wall movement may point toward a broader structural issue.
Crushed or displaced block
Broken units, opened bed joints and blocks that have shifted substantially from alignment are signs that more than surface mortar repair is required.
Unsafe conditions
If a wall appears unstable, heavily displaced or at risk of collapse, keep people away from the area and arrange prompt professional assessment rather than attempting a cosmetic repair.
Water Through Cracks
A crack can be a drainage problem even when it is not a major structural problem.
Water follows openings. A relatively limited crack can leak during heavy rain or spring melt if exterior drainage, grading or groundwater conditions are directing water toward the foundation.
Conversely, sealing the interior face of a leaking crack does not necessarily correct the exterior water load. Downspouts, surface grade, drains, window wells, exterior waterproofing and the condition of the foundation surface should be considered.
The structural significance of the crack and the moisture problem should therefore be evaluated separately. Sometimes both need repair. Sometimes drainage is the dominant issue.
Is a wet basement a foundation problem or a drainage problem? →
Water Clues
Look outside as well as inside.
✓Downspouts discharging beside the wall
✓Grade sloping toward the foundation
✓Poorly drained window wells
✓Damaged exterior parging or waterproofing
✓Water appearing after specific storms or snowmelt
Some foundation problems require reconstruction, not crack filling. When support or wall stability has been lost, the repair may involve reinforced concrete, masonry rebuilding, temporary support and engineering rather than a surface patch.
Repair Depends on Cause
Why crack filling is not the same thing as foundation repair.
A stable non-structural concrete crack may be repaired primarily to control water entry or protect the wall. A deteriorated mortar joint in otherwise stable concrete block may require masonry repair or repointing. Those are very different conditions from a bowed wall or a foundation undergoing settlement.
Structural repairs can include reinforcement, wall rebuilding, new support, underpinning, engineered stabilization or changes to drainage and soil loading. The correct scope depends on why the wall moved.
The American Concrete Institute notes that cracks are relevant to durability because they provide routes for water and aggressive agents, while cracks in load-carrying repairs can also affect structural performance. In other words, even a repair strategy has to reflect what the wall is expected to do.
Atlantic Canada Context
Why drainage, frost and seasonal moisture matter around foundations.
Atlantic Canadian foundations can see prolonged wet soil, spring snowmelt, freeze-thaw cycling, frost movement and concentrated roof runoff. These conditions do not explain every crack, but they can influence soil movement, moisture loading and deterioration of concrete block and mortar.
Where soil beside a foundation becomes saturated, water pressure and poor drainage can add to the demands on below-grade walls. Good grading and roof-water management therefore matter even when the visible symptom is a crack rather than a puddle.
Do Not Diagnose from Weather Alone
Climate can contribute to the conditions, but the wall still needs its own explanation.
Settlement, soil pressure, footing support, drainage, construction details and building loads can overlap. The crack pattern helps direct the investigation, not replace it.
Frequently Asked Questions
Common homeowner questions about concrete and block foundation cracks
What does a vertical crack in poured concrete mean?
Shrinkage is one common possibility, but settlement, restraint and loading can also create vertical or diagonal cracking. Displacement, location and whether the crack changes over time matter.
What does a horizontal crack in block mean?
In a below-grade wall, it can be associated with inward bending under soil or water pressure, particularly when the wall is also bowed or displaced.
What does a stair-step crack mean?
Stair-step cracking follows block mortar joints and can occur when part of the wall or footing moves differently from another part, including differential settlement.
Does every crack mean structural failure?
No. Many foundation cracks are not evidence of imminent failure. Bowing, leaning, offset, rapid change or loss of support are more concerning than a crack by itself.
Can a non-structural crack still leak?
Yes. Water can use a crack as a pathway even when structural movement is limited, so exterior drainage and waterproofing conditions still matter.
Do I need a mason or engineer?
A mason can assess masonry condition and repair feasibility. Significant movement, bowing, displacement, support concerns or uncertainty about structural behaviour are reasons to involve a structural engineer.
Related Knowledge Centre Guides
Use the crack pattern to connect the foundation problem to movement, water and repair.
Technical References
Further reading on concrete and masonry foundation cracking
Concrete Masonry & Hardscapes Association
CMU-TEC-009, Crack Control Strategies for Concrete Masonry Construction, discusses shrinkage, structural overload and differential settlement, including the characteristic stair-step cracking that can accompany settlement.
CMHA crack-control guidance →American Concrete Institute
ACI's technical guidance notes that cracking can occur in reinforced concrete foundation walls and that crack width and pattern are influenced by shrinkage and other time-dependent effects.
ACI foundation cracking FAQ →National Research Council Canada
The Illustrated User's Guide to the National Building Code explains how foundation walls resist lateral earth pressure and how wall support, backfill and surcharge loads affect their behaviour.
NRC foundation-wall guidance →Foundation Crack or Wall Movement?
Photograph the whole wall before focusing on the crack.
Include the full interior wall, close-ups of the crack, a side angle showing any bowing or offset, the floor and sill above, exterior grade and drainage, and any matching cracks on the outside.
About This Guide
Prepared from masonry field experience and structural reference material.
Prepared by Dean MacArthur, DinoMac Masonry Ltd., a third-generation mason with more than 20 years of hands-on masonry experience.
This guide is intended to help homeowners describe what they are seeing. Crack patterns can suggest possible mechanisms, but significant movement or structural uncertainty should be assessed on the actual building.
Reviewed August 26, 2026.
Not sure whether the wall needs a mason or engineer?
Use the mason-versus-engineer guide when the problem involves bowing, support, movement or structural design.
Mason or Structural Engineer?