# How to repair a cracked foundation

> A step-by-step guide to measuring foundation cracks, sealing the cosmetic ones, and recognising when a crack needs structural repair.

Canonical: https://foundationrepairlab.com/how-to-repair-a-cracked-foundation/

Last updated: 2026-11-09

How to repair a cracked foundation starts with a measurement, not a tube of sealant. Cracks at 1/16 inch or narrower are usually cosmetic, cracks at 1/8 inch need monitoring, and cracks that are wider, displaced, or leaking need injection or structural work. The repair method follows the number on the gauge.

## Measure the crack before you buy anything

Use a crack gauge or a set of feeler gauges and measure at three points: the widest part, and both ends. Write the width and the date next to each crack with a pencil, or photograph the crack with a ruler held against it. Then measure again in 30 days and again after the wet season.

Three measurements tell you what the crack is doing. A crack that stays at 1/16 inch through a wet winter and a dry summer is stable. A crack that opens from 1/16 inch to 1/8 inch in one season is moving, and movement is the signal that matters more than absolute width.

Also check for displacement. Run a straight edge across the crack. If one side stands proud of the other by more than a credit card thickness, the two sides have moved relative to each other, which points to settlement rather than shrinkage.

## Match the repair to the crack

| Crack type | Typical width | Likely cause | Repair |
|------------|---------------|--------------|--------|
| Hairline shrinkage | 1/16 inch or less | Concrete curing | Flexible sealant |
| Vertical mid-wall | 1/16 to 1/8 inch | Shrinkage or minor settlement | Monitor, seal if leaking |
| Diagonal stair-step | 1/8 inch or more | Differential settlement | Engineer review |
| Horizontal in basement wall | Any width | Lateral soil pressure | Wall anchors or straps |
| Crack with displacement | Any width | Settlement or heave | Piers or slab lifting |

Diagonal cracks that follow mortar joints in a brick wall are the classic settlement signature. They usually run from a corner of a window or door toward the corner of the building, and they widen toward the side that has dropped.

Horizontal cracks in a basement wall are a different failure. They usually sit near the middle third of the wall and come with inward bowing. Sealing that crack hides the symptom while the wall keeps moving.

## Sealing a cosmetic crack yourself

A stable crack at 1/16 inch or less can be sealed by a homeowner. The goal is to keep water and air out, not to restore structural continuity.

1. Clean the crack with a stiff brush and remove loose material with a vacuum.
2. Widen the surface slightly with a cold chisel or a crack chaser so the sealant has a keyway to sit in.
3. Fill with a polyurethane or silicone sealant rated for concrete, pressing it into the crack with a putty knife.
4. Tool the surface flush and wipe the edges before the sealant skins over.
5. Let it cure per the label, then check after the next rain for moisture.

Do not use a rigid patch on a crack that may still be moving. A brittle repair will crack again in the same place and tell you nothing new. A flexible sealant at least accommodates seasonal movement.

## When the crack is structural

Four conditions move a crack out of the DIY category.

The crack is at 1/8 inch or wider and growing. The wall has moved more than 2 inches out of plumb. The crack is accompanied by a sticking door, a sloping floor, or a gap at the wall and ceiling joint. Water is entering through the crack and the wall is damp.

Any one of those is enough to book an inspection. A structural engineer inspection typically costs $400 to $1,500 and produces a written opinion with a repair scope. That report is also what an insurer will ask for if you file a claim.

Injection is the middle path. Epoxy injection restores stiffness across a crack in a poured wall; polyurethane injection seals an active leak and stays flexible. Both are drilled and ported, then injected under pressure, and both need the crack to be stable enough that the repair is not chasing movement.

## What structural repair costs

If the diagnosis is settlement, the repair is priced by the unit.

| Repair | Unit | Typical range |
|--------|------|---------------|
| Push pier | each | $1,000 - $3,000 |
| Helical pier | each | $700 - $2,500 |
| Slab lifting | square foot | $3 - $12 |
| Wall anchor | each | $500 - $1,500 |
| Carbon fibre strap | each | $400 - $1,200 |

Six push piers at $2,000 each is 6 x $2,000 = $12,000, plus the $400 to $1,500 inspection. A wall with 4 anchors at $1,000 each is 4 x $1,000 = $4,000 for the lateral fix. The average foundation repair runs $4,000 to $15,000, and major work runs $20,000 to $40,000.

If repair costs approach one-third of replacement, replacement deserves a serious look. Replacement runs $40,000 to $150,000, so one-third of a $90,000 replacement is $29,700, which is the point where a repair quote needs justification.

## Stop the water that caused it

Most recurrent cracks have a water story. Check three things before or after the repair.

Grade. Soil should slope away from the wall at roughly 6 inches over the first 10 feet. A bed planted right against the wall holds water at the footing.

Downspouts. Discharge should land at least 4 to 6 feet from the wall, not at the corner where the crack is.

Drainage. A French drain or surface channel that moves water away from the perimeter is often cheaper than the structural repair it prevents.

## Bottom line

Repair a cracked foundation by measuring first. Seal the hairline cracks, monitor the 1/8 inch ones, and call an engineer when the crack is wide, displaced, or paired with a sloping floor. For pricing by crack type, see [foundation crack repair cost](https://foundationrepairlab.com/foundation-crack-repair-cost/) and [crack injection cost](https://foundationrepairlab.com/crack-injection-cost/). If the crack steps diagonally across brick, read [stair-step cracks repair](https://foundationrepairlab.com/stair-step-cracks-repair/) before you book anything.