Flaking concrete in Chicago is usually scaling: the surface skin peels off after water freezes in it, and deicing salt makes that worse. It is most common on concrete that lacked air entrainment, was finished wrong, or was salted in its first winter. Light scaling can often be resurfaced. Severe scaling that keeps progressing may not be repairable, and the slab gets replaced.
If the top of your Chicago sidewalk, stoop or driveway is peeling off in thin flakes and leaving a rough, pitted surface, you are looking at scaling. Many people call it spalling. It comes from one chain of events: water soaks the surface, it freezes and thaws over and over, deicing salt makes it worse, and the concrete was not built to take it. This article explains why that happens here, how to read the damage, and how it gets fixed.
What is scaling, and what failed?
The National Ready Mixed Concrete Association (NRMCA) defines scaling as flaking of the surface from freeze-thaw exposure (NRMCA). It comes in degrees. Light scaling does not expose the stone (aggregate) in the mix. Moderate scaling loses roughly 1/8 to 3/8 of an inch of the surface mortar (NRMCA).
It is different from two other things you may see on the same slab:
- Popouts. Small cone-shaped holes, about 1/4 inch to a few inches across, where a piece of absorbent stone near the surface froze while saturated and fractured (NRMCA).
- Cracks. A line through the slab, not a peeling surface. See which concrete cracks to worry about.
Why does it happen in Chicago?
Concrete that freezes while wet gets damaged unless it was made for it. NRMCA says concrete exposed to freeze-thaw cycles while wet should be air-entrained (NRMCA). Exterior concrete that sees freezing, constant moisture and deicing chemicals falls in the toughest durability class, called F3 in ACI 318, with ACI 332 as the residential equivalent (NRMCA).
Deicers make it worse. They raise how saturated the surface stays and add to the number of freeze-thaw cycles it goes through (NRMCA). We are not going to quote a cycle count for Chicago winters, because there is no honest single number. What matters is the pattern: wet, freeze, salt, thaw, repeat.
NRMCA lists the causes of scaling: concrete with no air entrainment or too little, low strength or permeable concrete, the wrong mix, too much deicer (especially on new concrete), bad finishing (working the surface while bleed water is still on it, or steel troweling), and not enough curing (NRMCA). Notice that most of those are decisions made on pour day.
Scaling often shows up on a stoop, walk or driveway that was poured at some point without much attention to finish and curing, then salted hard every winter. It starts on the edges and low spots where water sits, and it can look like the concrete is "wearing out" when the surface was weak from the start.
What are the warning signs?
- A rough, sandy or pitted surface where the smooth finish used to be.
- Thin flakes or scales on the surface, especially after winter.
- Gray grit on steps, in the gutter or at the bottom of a downspout.
- Damage concentrated where water pools or where salt gets shoveled.
- Small cone-shaped popouts appearing in the slab (NRMCA).
- Aggregate showing through the surface. That moves it from light to moderate.
How is scaled concrete fixed?
It depends on how far it has gone. NRMCA says minor scaling is cosmetic and may not need repair. Light to moderate scaling can be resurfaced with a repair mortar (portland cement, latex modified or polymer modified) after the unsound surface is removed. A repair is only as strong as the base it bonds to, and it will not match the original color. Severe, progressing scaling may not be feasible to repair (NRMCA). In that case, the slab comes out and is replaced. See sidewalk repair, replace or wait and concrete steps, repair or replace.
A new pour done right is built to resist this. NRMCA recommends for exterior slabs exposed to freezing and deicers: 4000 psi specified strength, air entrainment of about 6 percent for common stone sizes, no extra water at the site, finishing only after the bleed water is gone, a broom finish instead of steel troweling, proper curing, and a breathable silane or siloxane sealer as an option (NRMCA). Our winter pour article covers what changes in cold weather.
How should you use salt on concrete?
NRMCA's deicer guidance is straightforward (NRMCA):
- Avoid deicers on new concrete in its first winter if you can. Use clean sand for traction.
- After that, use moderate amounts. Sodium chloride and calcium chloride are considered acceptable for concrete.
- Never use ammonium sulfate, ammonium nitrate or magnesium based products.
- Hose off salt tracked in by vehicles when you can, and fix drainage that lets salt solution pool.
Too much deicer is only one item on NRMCA's list of causes. Cutting the salt helps, but it does not fix concrete that was poured wrong.
Scaling does not stop on its own. Each winter the exposed surface soaks, freezes and loses more. Light scaling that could have been resurfaced becomes severe, and NRMCA notes severe, progressing scaling may not be repairable (NRMCA). At that point the choice is replacement. If the slab is a public sidewalk, a rough or broken surface is also a trip hazard. See who pays for a broken sidewalk.
Do you need a permit to fix scaled concrete?
Check with the Department of Buildings before you assume either way. The City exempts installing, altering or removing a concrete sidewalk, patio or walkway on private property that is not in the public way and not more than 30 inches above grade, and exempts in-kind replacement of a concrete driveway or parking surface (City of Chicago). Work done under an exemption must still meet all construction codes (City of Chicago). A public way sidewalk is a different question, so confirm the route with the City.
Is your concrete flaking or pitted? Akats pours and replaces concrete in Chicago and can tell you whether it is resurfacing or replacement. See our concrete service and the Chicago concrete and sidewalk guide.
Common questions
Most likely scaling: the surface skin flakes off after freezing while wet, and deicing salt makes it worse. It is most common on concrete with no air entrainment, a weak mix, poor finishing or too little curing.
Light to moderate scaling can often be resurfaced after the unsound surface is removed. Severe scaling that keeps progressing may not be repairable, and the slab gets replaced. A repair will not match the original color.
Avoid deicers on new concrete in its first winter and use sand. After that, moderate amounts of sodium chloride or calcium chloride are considered acceptable. Never use ammonium sulfate, ammonium nitrate or magnesium based products.
Sources
- National Ready Mixed Concrete Association: Concrete in Practice 27: Cold Weather Concreting (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 2: Scaling Concrete Surfaces (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 40: Aggregate Popouts (PDF)
- National Ready Mixed Concrete Association: Concrete in Practice 44: Durability Requirements for Concrete (PDF)
- City of Chicago: Guide to Building Permits: Mason Contractor License FAQ
- City of Chicago: Guide to Building Permits: What Types of Work Do Not Require a Building Permit?
Facts last checked: October 7, 2026.
This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.