Quick answer
Concrete spalling is the breaking away of chips, flakes or larger pieces from the surface of concrete, which leaves a rough, shallow or deep pit. It happens when something inside or on the surface of the concrete pushes the outer layer off.
Common pushers are freezing water, deicing salts and rusting steel. Spalling is a clue about the cause, and by itself it does not say how sound the structure behind it is.
Quick facts
The key facts about Concrete Spalling, with sources:
- What it is
- Pieces of concrete breaking off a surface or edge 1
- Freeze-thaw role
- Freezing and thawing damage is serious in wet, freezing climates, worse with deicing salts 1
- Steel role
- Corroding steel creates expansive forces that can crack, spall and debond the concrete around it 1
- Thin cover
- Steel with too little concrete over it is more likely to corrode 1
- Related term
- Scaling is local flaking of a finished surface from freezing and thawing 2
- Prevention in new work
- Air-entrained concrete, proper finishing and curing, and limited deicers 2
- Repair rule
- A repair is only as strong as the surface it bonds to, so unsound concrete must come off first 2
Key takeaways
- Spalling is concrete breaking off in pieces. It is a symptom, and several different causes produce it 1.
- Freezing water and deicing salts are one cause. Rusting steel that swells inside the concrete is another 1.
- Scaling is the surface-flaking form that comes from freezing and thawing. Spalling can be deeper and tied to steel or joints 21.
- Steel with too little concrete cover is more likely to corrode 1.
- Spalling alone does not tell you whether a foundation is structurally sound. Depth, exposed steel, water and movement change the picture.
- A repair patch fails if it is bonded to weak concrete, so the cause and the base must be dealt with first 2.
What concrete spalling is
Spalling is the word for pieces coming off. You might see a chip at a corner of a step, a flaked patch on a basement wall, a pit in a slab edge or a crust that peels from a stem wall.
Sometimes the pieces are as thin as a coin. Sometimes they are big enough to show the rebar.
The term is used in repair guidance for roads and buildings alike.
The Federal Highway Administration (FHWA) talks about spalling in concrete pavement joints, and lists freezing and thawing, deicing salts and corroding steel among the causes 1.
A foundation is not a road, but the way concrete behaves under water, frost and rust is the same.
Spalling is different from the shrinkage cracks that form as concrete dries and is held back by the ground or the structure 4. See cracks in slab foundations for those, and reinforced concrete foundation for where the steel sits.
General information, not a diagnosis of your house
General information, not a diagnosis of your house. Spalling is a clue about water, frost, steel or construction. It cannot be graded from a photo or a description.
How spalling happens
Three mechanisms cause most spalling. The first is freezing water. Water gets into pores and cracks, freezes, expands and pushes the surface off. FHWA says freezing and thawing damage is a serious problem where the climate is wet and freezing, and that deicing salts and standing water often make it worse 1.
The second is rust. When steel inside the concrete corrodes, the rust takes up more room than the steel did.
FHWA says the corroding steel creates expansive forces that can crack, spall and debond the concrete around it, and that steel with too little cover is more likely to corrode 1.
Moisture alone can start it, even in climates that do not freeze 1.
The third is stress at joints and edges. FHWA notes that spalls can form when incompressible material gets into a joint and stops it closing as the concrete expands, which concentrates compression along the joint faces 1.
NRMCA likewise warns that joint edges in heavily trafficked floors need special attention to avoid spalling 3. For joints in a house slab, see foundation expansion joints.
- Moisture reaches the steelThrough pores, cracks or thin cover
- Steel corrodesRust forms on the bar
- Rust swellsIt creates expansive force around the bar
- Concrete cracksCracks run along or toward the surface
- A piece breaks offThe cover spalls and the bar is exposed
Source: [1]
Common causes and what they tend to look like
| Cause | How it can spall concrete | Where it shows up |
|---|---|---|
| Freeze-thaw with water | Water in pores freezes and expands; salts make it worse 1 | Surfaces that stay wet and freeze, such as steps and exterior slab edges |
| Deicing chemicals | Excess calcium or sodium chloride on weak or poorly cured concrete causes scaling 2 | Garage floors, porches and walkways near a foundation |
| Corroding steel | Rust expands and cracks the cover 1 | Along lines where bars sit, often with rust stains |
| Thin cover | Steel with too little concrete over it corrodes sooner 1 | Places where bars were set too close to the surface |
| Joint stress | Incompressible material in a joint stops it closing, loading the joint faces 1 | Slab joints and joint edges |
| Fertilizer chemicals | Ammonium sulfate and ammonium nitrate can scale concrete and attack it chemically 2 | Where lawn products spill on slabs and walks |
| Finishing and curing defects | Overworking bleed water or weak curing leaves a weak skin 2 | Newly built flatwork that flakes in its first winters |
Scaling
Deeper spalling
- Pieces break off, sometimes tied to steel corrosion or joint stress 1
- May expose steel and may signal a cause that continues
Example: reading a spalled step the way an inspector might
The spalled-step example is illustrative. It shows the questions asked, not a diagnosis. The step is an imagined concrete entry step at a house in a freezing climate.
| What is seen | What it can point to | What to check next |
|---|---|---|
| Thin flakes across the top face, no rust | Surface scaling from freezing and thawing, perhaps with deicers 2 | Was the concrete air-entrained? Were deicers used in the first winter? |
| A chip at the edge with a rust stain | Steel near the surface may be corroding 1 | How much cover exists? Is steel exposed? |
| A pit at a joint between slab and step | Joint stress or infiltration into the joint 1 | Is the joint filled and free to move? |
| Flaking that keeps growing each winter | An ongoing cause such as water or salt | Where does water sit, and what hits the step? |
The same three questions apply to a foundation wall or slab edge: what is wet, what is rusting and what is pushing. None of these rows says a foundation is unsound.
Where spalling shows up around a house
Spalling is most common on concrete that is wet, exposed and cold: steps, porches, garage aprons, driveway edges, patios and the top few inches of foundation walls above grade.
Inside a basement it can appear where a wall stays damp. Our efflorescence page covers the white salts that often travel with moisture in the same places.
On a foundation wall, spalled concrete can sit along a line of rebar, near grade where splashing water, snow and salt collect, or low on a wall that stays wet. In a slab, it can sit at joints and edges, where FHWA says joint stress can spall concrete 1.
Because each place has a different cause, location is the first clue. A chipped corner tells you less than a stripe of pits over a rebar line.
What spalling can tell you
What it is useful for
What it cannot tell you
- It does not say how deep the damage goes without a closer look; FHWA suggests coring to find the depth of deterioration in pavements 1.
- It does not show whether the structure is moving.
- It does not separate frost damage from corrosion by sight alone.
- A cosmetic patch can hide a continuing cause.
Limits of what you can learn from the surface
Spalling is a surface event. Behind it, concrete may be sound or may be soft for some depth. That depth decides what repair is suitable, and you cannot judge it by eye.
FHWA’s pavement guidance recommends coring representative locations to find the depth of deterioration before choosing a repair, and warns that a shallow, partial-depth repair is not suitable when the deterioration is deeper or tied to certain causes 1.
The same caution applies to a house. A shallow patch will not hold if the cause is still active, such as steel that is still corroding or water that keeps sitting on the surface. NRMCA puts it plainly for scaled surfaces: a repair is only as strong as the surface it bonds to 2.
Spalling also does not mean the same thing as a structural crack. A crack that passes all the way through a wall, a wall that bows, or a floor that moves is a different issue. See signs of structural foundation damage for those.
Spalling is not settlement
Spalling is about the concrete material failing at its surface. Settlement is the soil under a foundation moving. A house can have either, both or neither.
What drives repair cost
We do not print prices. Cost depends on the area and depth of damage, whether steel is exposed or corroded, how much sound concrete must be removed, access, the repair material and whether the cause (water, drainage, joints, cover) must also be fixed.
A small patch and a wall with corroded bars are very different jobs.
Cost also rises when the spalling is a symptom of something bigger, such as a wet wall or movement. Read our cost guide for how quotes are built. The cost calculator lets you test assumptions, and a written scope should say how deep the removal goes and how the base will be prepared.
How a surface repair is usually approached
A general outline of the usual order of work. It is not a do-it-yourself guide, and a structural wall needs an engineer’s direction.
- Find the cause: Water, frost, deicers, corrosion, joint stress or a finishing defect each need a different fix 12.
- Find the depth: Sound the area and, if needed, core to learn how deep the damage goes 1.
- Remove unsound concrete: NRMCA says all weak or unsound material must come off so the repair bonds to sound concrete 2.
- Clean and roughen the base: The surface should be clean, rough and textured before a bonded layer goes on 2.
- Place the repair: NRMCA lists portland cement concrete, latex-modified concrete and polymer-modified repair mortar as thin bonded resurfacing options for scaled surfaces 2.
- Protect it: Fix the drainage or exposure that caused the damage, or the new surface will fail again.
Slowing spalling on concrete you own
Slowing spalling takes safe, surface-level steps. They do not change the structure.
- Keep gutters and downspouts working and discharging away from steps, slabs and walls.
- Do not use deicing salts on concrete in its first year. NRMCA advises clean sand for traction instead and hosing off salt that cars deposit on new driveways 2.
- Never use ammonium sulfate or ammonium nitrate as a deicer. NRMCA says they can induce severe chemical attack on the surface 2.
- Sweep and clear standing water and snow piles off slabs near the house.
- Ask a concrete professional whether a breathable silane or siloxane sealer suits your slab. NRMCA mentions such sealers as a protection option and says to follow the manufacturer’s directions 2.
- Photograph and date spalled areas each season so you can show change to a professional.
Risks and when to call a structural engineer
Loose pieces can fall and injure someone at a step edge or overhead. Exposed steel keeps corroding. Water then has an easier path into the concrete, and the next freeze can take off more.
Spalling is a clue, not a diagnosis. Movement history, displacement, water, construction details and soil all change what it means. No pattern of chips tells you a wall is safe or unsafe.
Call a licensed structural engineer if the spalling is on a load-bearing wall, footing or beam and it is widening or changing; if rebar is exposed and rusting; if walls bow or are displaced; if doors and windows stick along with new cracks; if corners separate; or if you have any safety doubt.
Our engineer guide explains who to call.
Do not chip, grind or dig out spalled foundation concrete
Removing concrete from a load-bearing wall or footing can weaken it, and digging beside a foundation can undermine it. Leave structural work to an engineer-directed process. Wear eye protection near falling pieces and keep children away.
Codes and standards that touch spalling
Residential codes address durability through concrete requirements, not spalling by name. California’s 2025 residential code, in Section R402.2, requires air entrainment for concrete subject to moderate or severe weathering and sets minimum strengths by location 5.
It also says concrete exposed to deicing chemicals must follow limits on fly ash, pozzolans, silica fume, slag and blended cements in ACI 318 5. Other states adopt different editions.
Repair work on a structure often needs a permit and engineer involvement, especially when it touches a load-bearing member. Check with your building department. See foundation design and building codes for how codes get adopted.
Edition and adoption
The California text is cited as a state example as reproduced by a third-party site. Verify with the official code and your local building department.
Spalling compared with nearby terms
| Term | What it is | How it differs from spalling |
|---|---|---|
| Spalling | Pieces breaking off a concrete surface or edge 1 | This page |
| Scaling | Local flaking or peeling of a finished surface from freezing and thawing 2 | Usually shallower and tied to freeze-thaw exposure |
| Efflorescence | Salt deposits left on a surface as moisture dries | See foundation efflorescence; it is a deposit, not a loss of concrete |
| Surface peeling without frost | NRMCA notes concrete can peel or scale without freezing, often from early steel troweling or finishing while bleed water is present 2 | A finishing defect, not weather |
Spalling myths
- Myth Spalling means the foundation is failing.
- Reality Spalling is a surface or cover problem. It can have a minor cause or point to a continuing one. It needs a closer look, not a verdict.
- Myth A skim coat or paint will fix it.
- Reality NRMCA says a repair is only as strong as the surface it bonds to, so weak concrete must be removed first 2.
- Myth Only cold climates get spalling.
- Reality FHWA says moisture can corrode steel and spall concrete even in non-freezing climates 1.
- Myth Salt is harmless on a driveway.
- Reality Deicing salts can scale concrete, especially new or weak concrete 21.
- Myth Stronger concrete never spalls.
- Reality Air entrainment, cover, curing and drainage matter as much as strength. See concrete compressive strength.
Regional factors for spalling
Climate decides which cause dominates. In regions with many freeze-thaw cycles and road or driveway salts, frost damage and scaling are common, and FHWA says wet, freezing climates make the damage worse 1.
Code tables in such regions ask for air-entrained concrete 5. In warm regions with no frost, corrosion of steel from moisture is the main worry 1.
High water tables and poor drainage raise moisture almost anywhere. Ask your building department what weathering class applies and how drainage is expected to work.
What to do with this
Start by recording the spalling: photos with a coin or ruler in frame, dates and a sketch of where it sits. Then ask where the water goes. The water intrusion tool helps you think through moisture sources, and the crack identification tool helps you log cracks nearby.
- If Thin flakes on an outdoor step, no cracks in the house
- Then Photograph, keep water and salt off it, and ask a concrete professional about repair
- If Rust stains or exposed rebar
- Then Ask a licensed professional about the cover and the cause; steel keeps corroding
- If Spalling on a basement wall that stays damp
- Then Look at drainage and moisture first; see the water intrusion tool
- If Spalling with new cracks, bowing or sticking doors
- Then Call a licensed structural engineer
Questions about Concrete Spalling
What causes concrete spalling?
The main causes are freezing water in the concrete, deicing salts, corroding steel that swells inside it and stress at joints and edges. FHWA lists freeze-thaw damage, corrosion of steel and joint-related factors 1. Poor finishing or curing can also leave a weak surface that flakes 2.
Is spalling concrete dangerous?
Loose pieces can fall or trip someone, and exposed steel keeps corroding. Whether the spalling signals a structural problem depends on where it is, how deep it goes and what is behind it. A licensed structural engineer evaluates that. Spalling by itself is a clue, not a diagnosis.
What is the difference between spalling and scaling?
NRMCA defines scaling as local flaking or peeling of a finished surface from freezing and thawing 2. Spalling is the broader term for pieces breaking off, and it can be deeper and linked to rusting steel or joint stress 1. The two can look alike.
Can spalled concrete be repaired?
Often, yes, but the cause must be dealt with first. A repair is only as strong as the base it bonds to, so unsound concrete must be removed and the base cleaned and roughened 2. How deep the damage goes decides which method suits. A structural member needs an engineer’s direction.
Why does spalling expose rebar?
Because the concrete cover over the bar is thin or has broken away. FHWA says steel with too little cover is more likely to corrode and that corroding steel creates expansive forces that can crack and spall the concrete around it 1. Exposed steel keeps rusting until it is dealt with.
Does spalling mean my foundation is failing?
Not by itself. Spalling can be a surface or cover problem. It can also come with moisture or movement that needs attention. No pattern says a foundation is safe or unsafe. See an engineer if the spalling is on a load-bearing member and is widening, or comes with cracks, bowing walls or sticking doors.
Do deicing salts cause spalling?
They can. NRMCA says excess calcium or sodium chloride on concrete with inadequate strength, air entrainment or curing causes scaling, and advises no deicers in the first year after placement 2. FHWA adds that salts make freeze-thaw damage worse in wet climates 1.
Can I seal concrete to stop spalling?
A sealer may help slow water entry, but it is not a cure. NRMCA mentions breathable silane or siloxane sealers for slabs, or a boiled linseed oil and mineral spirits mixture as protection options for slabs, alongside air entrainment and proper curing 2. Follow the manufacturer’s directions and ask a concrete professional.
Should I call a contractor or an engineer for spalling?
For small surface damage on flatwork, a concrete repair professional is usually fine. For spalling on a foundation wall, footing or beam, or with rust, widening or other signs, ask a licensed structural engineer first. The engineer or contractor tool helps you decide.
Sources
- Federal Highway Administration, Concrete Pavement Preservation: Partial-Depth Repairs, “Selection of Candidate Projects” (page updated 2017), retrieved .
- NRMCA, CIP 2 – Scaling Concrete Surfaces (1998), copy hosted by Prairie Material, retrieved .
- NRMCA, CIP 6 – Joints in Concrete Slabs on Grade (1998), copy hosted by Prairie Material, retrieved .
- NRMCA, TIP 17 – Drying Shrinkage of Concrete, retrieved .
- 2025 California Residential Code, Section R402.2 Concrete (Title 24, Part 2.5), as reproduced by GoCodeBook; third-party copy, verify against the official publication, retrieved .
Expert review
Written by the HyreFoundation Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Facts were checked against the FHWA, NRMCA and California code documents listed above, retrieved 2026-10-14. FHWA guidance is written for concrete pavement and is used here for the mechanisms of spalling, not as a house repair method. No structural engineer has reviewed this page.
Suggest a correction. We fix errors and say what changed.