# Foundation Cracks: Which Ones Are Normal and Which Need Repair
> Many small foundation cracks come from concrete shrinking as it cures. Learn which cracks are normal, which point to movement, and how each is repaired.
_Brian Dalinghaus ยท 2026-10-31_
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Foundation cracks are common, and many of them are a normal part of how concrete behaves. Thin cracks that appear as a slab or stem wall dries and shrinks usually stay small and stable. Cracks that widen over time, cracks where one edge has dropped below the other, and cracks that show up with sticking doors or uneven floors can point to a foundation that is moving. This guide explains how to tell the two apart on the slab and raised foundations most homes in Southern California, Arizona and Nevada sit on, how to track a crack, and how [[silo:foundation-repair|foundation repair is matched]] to the cause.
## Why Do Foundations Crack at All?
Concrete shrinks as it dries, and that shrinking pulls on the slab or wall until it cracks somewhere. Cracking is a normal part of concrete construction. Builders cut control joints into slabs to help decide where those cracks form, but control joints manage cracking. They do not stop it.
The soil under a home also moves. Clay soil acts like a sponge beneath your home. It expands when wet and contracts when dry, which can cause the foundation above it to move. When one part of a foundation moves more than another, the concrete can crack where the stress builds up.
So a crack can come from two very different things: the concrete itself shrinking, or the ground under it shifting. The first is usually cosmetic. The second is the kind that may need repair, and the clues below help you tell which one you are looking at.
## Which Foundation Cracks Are Normal?
Small cracks that form as new concrete dries and shrinks are common, and most of them do not affect the strength of the slab, according to the [National Ready Mixed Concrete Association](https://www.nrmca.org/wp-content/uploads/2021/01/04pr.pdf). These are the cracks most homeowners find first, and they are usually not a reason for concern on their own.
### Hairline Shrinkage Cracks
Hairline cracks are thin, often irregular lines in a slab, a garage floor or a stem wall. They tend to show up in the first few years after the concrete is poured. You may spot them when you pull up old carpet, move a cabinet in the garage, or look closely at the exposed concrete along the base of the house.
A hairline crack is usually cosmetic when both sides sit level with each other, it stays the same size from season to season, and nothing else in the house has changed. However, it is still worth taking a dated photo so you have something to compare against later.
### Small Vertical Cracks in a Stem Wall
On a raised foundation, the stem wall is the short concrete wall that runs around the edge of the house and holds up the framing. A thin vertical crack in a stem wall, running straight up and down, often comes from shrinkage. It can be harmless when it stays narrow and even, with no step or offset from one side to the other.
### Cracks Along Control Joints
A crack that runs along a control joint, the straight groove cut into a slab or driveway, is often the slab doing what the joint was designed for. Cracks that wander away from the joints are common too. What matters more than where a crack starts is whether it changes.
## Which Foundation Cracks Need a Closer Look?
A crack is worth having evaluated when it shows signs of movement: one side higher than the other, growth over time, a crack that returns after patching, or a pattern that suggests the ground below has shifted. A crack's direction can hint at a cause, but direction alone does not decide whether a repair is needed.
### Cracks With One Side Higher Than the Other
When you can feel a lip as you run your hand or shoe across a crack, one side of the concrete has moved up or down relative to the other. That offset can point to settlement under one part of the slab or to soil pushing up under another part. It is one of the clearest differences between a shrinkage crack and a movement crack.
### Cracks That Keep Growing or Come Back After Patching
A crack that gets longer, wider or starts branching into new cracks is telling you something is still moving. The same goes for a crack that reopens after it was filled or painted over. Patching closes the gap at the surface, but it does not change whatever is pulling the concrete apart.
### Horizontal Cracks Along the Foundation Line
On many homes in the areas we serve, the foundation is mostly hidden behind stucco. A crack that runs sideways through the stucco near the bottom of the wall, close to where the house meets the foundation, can be a sign that the foundation below has shifted. Home inspectors sometimes flag these exterior cracks and recommend a foundation evaluation before a sale closes.
### Diagonal and Stair Step Cracks
[[sign:foundation-repair/diagonal-cracks|Diagonal cracks]] that run at an angle, often wider at one end than the other, can come from one part of the foundation settling more than the part next to it. In block walls and textured stucco, the same kind of movement can leave [[sign:foundation-repair/stair-step-cracks|stair step cracks]] that zigzag across the surface. These patterns are worth an evaluation, especially when they show up near doors and windows.
### Wide or Branching Cracks Across a Slab Floor
Inside a slab home, the foundation is the floor. Wide cracks that cross a room, split into several branches, or line up with tile that keeps cracking in the same place can point to slab movement. These often go unnoticed until flooring comes up during a remodel. If you find [[sign:foundation-repair/floor-cracks|cracks in a concrete floor]] like these, photograph them before new flooring goes down.
## Where Do Foundation Cracks Show Up on Slab and Raised Foundation Homes?
Most homes in Southern California and Arizona are built on a concrete slab or a raised foundation with a crawl space, and in both cases the foundation itself is hard to see. Cracks often show up first in the materials resting on it.
- **Stucco.** [[sign:foundation-repair/stucco-cracking|Stucco cracking]] along the base of the wall or spreading from window and door corners can reflect movement below.
- **Drywall.** [[sign:foundation-repair/drywall-cracks|Drywall cracks that angle up]] from the corners of doors and windows, or run where the wall meets the ceiling, can follow the same movement.
- **The slab under flooring.** Cracked tile, grout lines that keep opening, and a lip under vinyl or laminate can trace a crack in the slab below.
- **The garage floor.** Garage slabs are often the one place where you can see the bare concrete, which makes them a good spot to watch.
- **The stem wall.** On raised foundation homes, the exposed concrete along the base of the house is where foundation cracks are easiest to see from outside.
## What Other Signs Point to Foundation Movement?
A single crack is hard to judge on its own. A crack that appears along with changes elsewhere in the house is a stronger sign that the foundation may be moving. These signs can point to movement:
- Doors and windows that start sticking, rubbing or no longer latching.
- [[sign:foundation-repair/gaps-around-windows-doors|Gaps around windows]] and doors that are wider at one end of the frame than the other.
- Floors that slope, feel uneven underfoot, or let a marble roll toward one side of the room.
- Baseboards or cabinets pulling away from the wall.
- Cracks in drywall that start at the corners of door frames and run toward the ceiling.
None of these proves a foundation problem by itself. Sticking doors can come from humidity, and drywall can crack at a seam for reasons that have nothing to do with the foundation. What helps is noticing when several signs appear around the same time or in the same part of the house.
## How Can You Tell if a Foundation Crack Is Getting Worse?
The most useful thing a homeowner can do is track the crack over time, because a stable crack and a growing crack can look the same on the first day. A simple record makes a later evaluation more accurate too.
1. Mark each end of the crack with a short pencil line and write the date beside it.
2. Measure the width at its widest point with a ruler or a crack gauge, and write that down with the date.
3. Take a photo with a coin or tape measure in the frame so the scale is easy to compare later.
4. Check the crack again every few months and after heavy rain or a long dry spell, when soil moisture changes the most.
5. Note any new symptoms, such as a door that has started to stick, in the same record.
If the crack grows past your pencil marks, gets wider, develops a lip, or new cracks appear nearby, that is the point to have it looked at. A record of how the crack changed gives whoever evaluates it a clearer picture than a single visit can.
## What Causes Foundation Cracks in California, Arizona and Nevada?
Foundation cracks usually trace back to the concrete itself or to changes in the soil beneath it. In the areas Dalinghaus Foundation Repair serves, several causes come up often.
- **Concrete shrinkage.** Concrete shrinks as it cures, and the small cracks that result are common in new slabs and stem walls.
- **Expansive clay soil.** Clay soils swell when they get wet and shrink as they dry, so slabs and foundations on clay can move up and down with the seasons. Learn more about [[sign:foundation-repair/expansive-soil|how expansive soil affects a home]].
- **Water near the foundation.** Downspouts that empty against the house, irrigation that soaks one side, and yards that slope toward the home can keep the soil wetter on one side than the other.
- **Fill that was not compacted well.** Fill placed under a slab during construction may not have been compacted in even layers, and it can keep compressing under load for years, taking the slab with it.
- **Old utility trenches.** Soil placed back into utility trenches often settles more than the soil around it, so a low line across a floor can sometimes follow an old trench.
Some of these causes stop on their own, such as shrinkage in a new slab. Others, such as uneven soil moisture or soft fill, can keep working until the cause is dealt with. That is why the cause matters as much as the crack.
## Can You Fix a Foundation Crack Yourself?
You can often seal a small, dry, stable crack in a garage slab or walkway yourself with a concrete crack filler, mainly to improve its look and keep out dirt and moisture. Sealing a crack does not stop the movement that caused it. If the crack was formed by soil shifting under the slab, it may reopen next to the patch or somewhere nearby.
Before you fill any crack, take a dated photo and a measurement first. Filling it erases the evidence of whether it was growing. For cracks with a lip, cracks that keep returning, or cracks that come with other signs of movement, an evaluation is the better first step.
## How Are Foundation Cracks Repaired?
Foundation cracks are repaired by first finding what caused the crack and then choosing a repair for that cause. At Dalinghaus Foundation Repair, our approach to [[service:foundation-repair/foundation-crack-repair|foundation crack repair]] is to look for what caused the crack first, then seal stable cracks with structural epoxy injection. When the foundation is still moving, the repair usually starts below the crack.
### Sealing Stable Cracks With Epoxy Injection
When a crack is stable and the foundation is not moving, [[solution:foundation-repair/epoxy-crack-injection|epoxy crack injection]] fills the crack and bonds the concrete on both sides. On a slab, the crack is usually cleaned out and marked first, then filled along its length.
### Stabilizing a Settling Foundation With Piers
When part of a foundation is settling, sealing the crack alone would only treat the symptom. [[solution:foundation-repair/push-piers|Steel push piers]] or [[solution:foundation-repair/helical-piers|helical piers can be installed]] under the foundation to support it on deeper soil and help stabilize it against further settlement. Piers support the foundation from below. They do not always close the cracks that are already there, so some cracks may still need sealing or cosmetic repair after the foundation is stable.
### Filling Voids Under a Slab
When a slab has cracked because the soil under it has washed out or compressed, polyurethane foam can be injected through small holes drilled in the slab to fill the empty space and help support and lift the concrete. Slab movement is watched during the injection. For more on how a slab is assessed and repaired as a whole, see our page on [[service:foundation-repair/slab-foundation|slab foundation repair]].
### Why Does a GPR Scan Come Before Interior Slab Work?
Before any interior work on a slab, Dalinghaus Foundation Repair requires a ground penetrating radar (GPR) floor scan, and it is always required on a post tension slab. A post tension slab has steel cables running through it under high tension, and the scan shows where they are before anyone drills. This is a common question from homeowners with post tension homes who have found light cracking in their slab. The scan is a separate step from the crack repair itself.
## What Happens During a Foundation Evaluation?
A foundation evaluation looks at the crack together with everything around it, so the recommendation fits the cause. During a [[service:foundation-repair/foundation-inspection|free foundation evaluation]], a Dalinghaus specialist usually looks at the cracks you have found, checks how level the floors are, and looks for related signs inside and outside the home.
Bring your notes and dated photos if you have been tracking a crack. They show how the crack has changed, which is hard to judge from one visit. Some cracks need nothing more than monitoring. Others call for crack sealing, and some point to movement that needs to be stabilized first. The goal is the appropriate repair for your home, which is not always the largest one.
## Should You Worry About Foundation Cracks When Buying a Home?
Cracks in a home you are buying are worth understanding before escrow closes, but many of them turn out to be normal shrinkage. Home inspectors often note exterior or slab cracks and recommend a foundation evaluation so the buyer knows what the cracks mean.
A [[service:foundation-repair/real-estate-inspection|foundation inspection during escrow]] can help you learn whether a crack is cosmetic or tied to movement, and what a repair would involve if one is needed. That gives you clearer information for your decision and any conversation with the seller.
## Frequently Asked Questions About Foundation Cracks
### Are hairline cracks in a foundation normal?
Small cracks that form as new concrete dries and shrinks are common, and most of them do not affect the strength of the slab. A hairline crack is usually cosmetic when both sides sit level with each other, it stays the same size from season to season, and nothing else in the house has changed.
### How can you tell if a foundation crack is structural?
A crack is worth having evaluated when it shows signs of movement: one side higher than the other, growth over time, a crack that returns after patching, or a pattern that suggests the ground below has shifted. A crack's direction can hint at a cause, but direction alone does not decide whether a repair is needed.
### Can you fix a foundation crack yourself?
You can often seal a small, dry, stable crack in a garage slab or walkway yourself with a concrete crack filler, mainly to improve its look and keep out dirt and moisture. Sealing a crack does not stop the movement that caused it.
### Do foundation piers close existing cracks?
Piers support the foundation from below. They do not always close the cracks that are already there, so some cracks may still need sealing or cosmetic repair after the foundation is stable.
If you have found a crack and are not sure what it means, schedule a free evaluation with Dalinghaus Foundation Repair. We will look at the crack, the signs around it and the likely cause, and explain what we would recommend and why.