Crack in a Retaining Wall: Causes and Repairs

Are cracks in a retaining wall normal?

Fine cracks are common in concrete and masonry and are not necessarily a problem. Concrete shrinks as it cures, and it often cracks to some degree. But a retaining wall also holds back soil, and water and soil add a great deal of load. So a retaining wall crack deserves more attention than a similar crack in a garden path. The first task is to work out whether the wall is stable and why it cracked, before you patch anything.

What the crack pattern suggests

These are general patterns, not diagnoses.

Hairline vertical cracks. Often from curing shrinkage or temperature movement, and frequently cosmetic. They can still let water in, so sealing them is reasonable if the wall is stable.
Vertical or stair-step cracks. Can point to uneven settlement or erosion under the footing, or to missing movement joints.
Horizontal cracks. Generally more worrying, as they can indicate that soil or water is pushing the wall outward. See also what a horizontal wall crack means.
Widening gaps, a leaning or bowing wall. Signs that the wall may be failing. Gaps wider than about 1/2 inch, or cracking together with tilt, justify prompt professional input.

Common causes

Poor drainage. Water collecting behind the wall builds up pressure (hydrostatic pressure) and adds weight to the soil. This is widely cited as the most common cause.
Missing or blocked drains. Retaining walls are normally designed with drainage such as gravel backfill, perforated pipe or weep holes. If these are absent or clogged, pressure can build. See retaining wall base material for how the base and drainage stone are normally built.
Frost and freeze-thaw. Water in saturated soil that freezes can exert force on the wall.
Tree roots. Growing roots can push on a wall or footing.
Overloading. Driveways, vehicles, structures, or additional soil above the wall that the design did not allow for.
Settlement or footing problems. Soft or eroded soil under the footing.
Construction faults. Inadequate reinforcement, no control joints, or a wall too slender for its height.

Safety first: signs of a failing wall

A retaining wall that fails can come down suddenly and injure people. Keep people and pets away from the wall and the area just below it if you see:

leaning, bulging or bowing,
widening cracks, or sections that have shifted or dropped,
soil washing out from the base or through cracks,
gaps opening between wall sections.

Do not stand or work at the base of a wall that looks unstable. Contact a structural or geotechnical engineer or an experienced retaining wall contractor. Many places require a permit and an engineered design for walls above a certain height, often around 4 feet, though the limit varies by location; check with your local building department.

How to assess the wall

Photograph and measure the crack, and note the date. Mark the ends of the crack in pencil.
Check plumb. Use a level or a string line to see whether the wall leans or bows.
Look at drainage. After rain, check for pooling behind the wall, wet patches, weep holes that are blocked, and downspouts or sprinklers discharging towards it.
Look at the base. Is soil eroding in front of the wall? Is the footing visible or undermined?
Note what is above. Are there new loads, trees or structures close to the top?
Monitor for several weeks or months, especially through wet periods or freeze-thaw changes.

Repairing minor cracks

If the wall is stable and the crack is small (some guidance uses under about 1/8 inch), a DIY repair is reasonable:

Wear eye protection and gloves.
Chip away loose material with a hammer and chisel, and brush the crack clean. Washing out dust and letting the area dry or dampening it as the product directs are typical steps.
Fill with a flexible masonry sealant or a concrete crack filler suited to vertical surfaces. Narrow stable cracks may suit an injectable repair; see how to repair a crack in a concrete wall for material choices and a step-by-step approach.
Smooth the surface and allow it to cure according to the label.

Remember that a patch does not stop whatever caused the crack. If the crack reopens or the wall moves, stop patching and have it assessed.

Cinder block (concrete block) walls

For stable hairline cracks in a block wall, a masonry crack filler or elastomeric sealant labelled for masonry is commonly used. Cracks in the mortar joints of a block wall may be raked out and repointed with suitable masonry mortar. Stair-step cracking along mortar joints, bulges or displaced blocks suggest movement, and the cause should be found. Block walls that are leaning need professional assessment. Block retaining walls normally rely on reinforcement and grouted cores, so structural cracks need an engineer.

Fixing the cause: drainage

Often the most valuable step is to improve drainage, not just to fill the crack:

Keep gutters and downspouts discharging well away from the top and base of the wall.
Clear any weep holes or drain outlets.
Check that the soil behind the wall is not sloping water towards it.
Avoid heavy irrigation next to the wall, and repair any leaking irrigation system that wets the soil behind it.
Where drainage behind the wall is absent, retrofit options exist, but they usually involve excavation and are best planned with a contractor or engineer.

Leaning or failing walls: professional repair

How to fix a falling retaining wall depends on its type, height and condition. Options a professional might consider include excavating and rebuilding with proper drainage and reinforcement, adding anchors or tiebacks, installing a drainage system behind the wall, or replacing it. Stabilising a leaning wall is not a quick DIY job, and the soil behind it can release suddenly during work. Get an engineer’s opinion and, where required, a permit.

Does homeowners insurance cover a falling retaining wall?

Often not fully. Many policies treat retaining walls as other structures, and cover may exclude damage from earth movement, water pressure, wear or poor maintenance, while some specified events may be covered. Details vary a great deal by policy, so check your wording and ask your insurer, and document the damage with dated photographs.

FAQ

How do I fix a falling retaining wall?

Keep clear of it, and get a structural or geotechnical engineer or experienced contractor to assess it. Repairs usually include fixing drainage and may involve rebuilding or adding reinforcement.

What is the best crack filler for cinder block walls?

A masonry crack filler or elastomeric masonry sealant that is labelled for block and suited to the crack width. Mortar repointing suits cracked joints. Follow the label.

Is it normal to have cracks in your walls?

Small cracks are common in concrete and masonry, including retaining walls. Wide, growing or leaning cracks are not something to ignore.

Will homeowners insurance cover a falling retaining wall?

It depends on the policy and the cause, and many exclude earth movement or gradual deterioration. Ask your insurer.