Vertical cracks in poured concrete are often associated with shrinkage, but they can still leak or reflect movement. Horizontal cracks can be associated with lateral pressure and wall bowing. Stair-step cracks through block or masonry joints can follow movement in the wall or footing. No direction proves the cause by itself. Look for displacement, widening, bowing, related movement and change over time, and arrange structural evaluation when those warning signs are present.
What to know
- Crack direction is a clue, not a remote diagnosis.
- Horizontal cracks, bowing and displacement deserve timely structural review.
- A stable leaking crack and a moving structural crack need different repair paths.
- Document changes, but do not delay on sudden or severe movement.
Vertical and diagonal cracks
A narrow vertical crack in poured concrete may form as concrete cures and shrinks. It can still become a water path. Diagonal cracks near openings or changes in wall height may reflect stress concentration, shrinkage or movement. Width, endpoints and displacement matter more than a label alone.
Injection or localized exterior repair may be suitable for a stable leaking poured-concrete crack. Before sealing, the inspector should check the full height, exterior water concentration and whether the two sides remain in the same plane.
Horizontal and stair-step cracks
Horizontal cracking across a wall can appear where lateral pressure is affecting block, concrete or masonry. Look for inward bowing, separation at the top, displaced units or repeat cracking after patching. Prompt structural-capable evaluation is appropriate even when the wall is not visibly failing.
Stair-step cracks follow mortar joints in block, brick or stone assemblies. They may reflect settlement, rotation, movement near an opening or local deterioration. Repointing the joints is not a complete repair when movement remains active.
Warning signs beyond the crack
The wall shape and the rest of the building provide context. Sticking doors, uneven floors, separated trim or an addition pulling away may or may not be related, but they should be documented. Water, erosion, failed supports and changes around the property can also inform the evaluation.
Sudden change, falling masonry, severe displacement or an unstable support is a safety concern. Leave the area and seek urgent professional help instead of measuring or attempting a temporary patch.
- Visible bowing or bulging
- One side of the crack offset from the other
- Rapid or measurable widening
- Related floor or framing movement
- Crushed, spalled or falling masonry
- Previous repairs that reopened
What to ask the evaluator
Ask whether the visit is a repair estimate, a structural inspection or an engineering opinion. Request measurements and an explanation connecting observations to the proposed method. If a proprietary brace, anchor or pier is recommended, ask what condition it addresses and whether design or permit documentation is required.
If monitoring is reasonable, agree on measurement locations, interval and the condition that triggers action. Monitoring should be written down; casual photos without scale are difficult to compare.
A field guide to crack direction
Crack direction is a clue, not a verdict. The same pattern can come from more than one cause, so a crack is best read alongside the wall, the floor above it and the drainage outside.
| Crack | Usually points to | How urgent |
|---|---|---|
| Vertical, thin, near the middle of the wall | Shrinkage in the concrete | Usually low; seal if it leaks |
| Diagonal from a corner | Differential settlement | Monitor and evaluate |
| Horizontal | Lateral soil pressure | Get evaluated promptly |
| Stair-step in block | Movement along mortar joints | Evaluate the cause |
Sources and Vermont specifics
Displacement is the tie-breaker
InterNACHI describes shrinkage cracks as showing no vertical displacement, and calls cracking in slabs and foundation walls inevitable and expected. That gives a tie-breaker for crack direction: a crack in which one side has moved relative to the other, by even a fraction of an inch, needs more attention than one whose edges still line up.
Record the crack on a dated photograph with a ruler beside it, and mark the ends with a pencil and the date. Measure again in a season. A crack that is unchanged after a full freeze-thaw and wet-dry cycle is telling you something different from one that has lengthened or widened.
Sources: InterNACHI, Shrinkage Cracks in Concrete. Checked September 26, 2026.
Frequently asked questions
How do I measure whether a crack is moving?
Mark each end with a dated pencil line and measure the width at a marked point with a crack gauge or calipers. Photograph it with a scale in frame. Repeat seasonally. A measured record answers next year's question; a memory of how it looked does not.
How wide is too wide for a foundation crack?
Width is only one factor. A narrow displaced or changing crack may be more important than a wider stable surface crack. Direction, wall shape, foundation type, water and change over time determine the need for structural review.
Can I fill a horizontal crack with hydraulic cement?
A surface fill may hide the line without addressing lateral movement or water pressure. Horizontal cracking should be evaluated before it is concealed so the wall condition and appropriate stabilization can be documented.
General information, not a diagnosis of your property. Editorial policy