Pieces are coming off your concrete, and every article you open calls it something different: flaking, chipping, scaling, spalling. The words overlap in everyday speech, but concrete engineers use some of them for specific kinds of damage, and the right fix depends on which kind you have. This guide sorts them by depth and timing, then matches each one to a repair.
I read the NRMCA Concrete in Practice sheets on scaling (CIP 2), delamination (CIP 20) and dusting (CIP 1), the ACI repair bulletin on spalls in horizontal slabs (RAP-7), and a 2023 brief on surface distress from the Iowa State University concrete pavement center. I did not test any concrete. Where a source covers pavements or buildings rather than a home driveway, I say so.
The short answer
Look at how deep the loss is and how old the concrete is. A thin skin peeling off in patches, usually after winter, is scaling. Thin sheets that sound hollow in a slab less than a few years old are usually a finishing problem called delamination. Chunks that break away, especially with rust stains or exposed steel, are spalling, and that is a repair job rather than a touch-up. Cone-shaped holes with a broken stone at the bottom are popouts, which nothing can prevent once the stone is in the slab.
Which one do you have?
| What you see | Usual name | Depth the sources give | Usual cause |
|---|---|---|---|
| Skin peels in patches, stones start to show, mostly after winter | Scaling | Light scaling leaves the coarse stone covered. Moderate scaling exposes it and can remove up to 1/8 to 3/8 inch (3 to 10 mm) of surface mortar (NRMCA CIP 2) | Freeze-thaw cycles in wet concrete, made worse by deicing salts |
| Thin sheets lift off, the area sounds hollow when tapped, slab is young | Delamination | Usually 1/8 to 1/4 inch (3 to 6 mm) (NRMCA CIP 20) | Surface finished too early or too hard, trapping bleed water and air underneath |
| Thin flakes come off with a hammer tap, sound concrete underneath | Flaking | Surface only (Iowa State brief) | Finishing while bleed water was on the surface, or smooth aggregate that never bonded well |
| Cone-shaped holes with a broken stone at the bottom | Popouts | The depth of one stone | Porous stone such as chert that soaks up water and expands when it freezes |
| Chunks break away, rust stains, bars showing | Spalling from corrosion | Down to or past the steel (ACI RAP-7) | Rust expands and pushes the concrete cover off |
| Fine powder comes off under traffic, a nail scratches it | Dusting | A weak top layer (NRMCA CIP 1) | Bleed water worked into the surface, poor curing |
The terms are used loosely. NRMCA reserves “scaling” for freeze-thaw damage and notes that concrete can also peel without freezing when it was finished too early or too hard. The Iowa State brief uses “flaking” for that early finishing damage. If an article calls everything spalling, treat that as a loose label and use the depth and the timing to decide what it is.
Three quick checks
- Tap it. A hollow sound over a thin layer points to delamination. NRMCA describes tapping with a hammer or dragging a heavy chain over the slab to find it. Thin flakes that pop off the surface with sound concrete below point to flaking.
- Look for rust. Brown stains, cracks following a straight line, or visible steel mean corrosion, which puts the problem in the spalling and repair-job column.
- Note when it started and where. Damage in the first year, spread evenly, suggests how the slab was finished. Damage that appears after winters, concentrated at edges, near drains or where cars park and drip salty slush, suggests freeze-thaw and salt.
Why is my new concrete flaking?
When a young slab flakes or scales, the usual suspect is how it was placed and finished. NRMCA lists the common causes: finishing while bleed water was still on the surface, overworking the surface, steel troweling an exterior slab, adding extra water at the job site, and poor curing. Bleed water worked into the top layer raises its water content and weakens it, and overworking removes the tiny air bubbles that protect against freezing. The Iowa State brief adds that hand-placed concrete tends to show more of this than machine-placed concrete.
The same NRMCA sheet advises against deicing salts in the first winter. New concrete is more porous and weaker, so salt on it is the fast route to scaling. If you can, spread clean sand for traction instead.
What to do about it depends on how bad it is. NRMCA says minor scaling is cosmetic and may not need repair. If it is widespread and came right after a pour, photograph it, tell the contractor promptly in writing, and keep the dates. That last step is my suggestion, not something from the sheets.
Why is my older concrete scaling or chipping?
NRMCA explains the mechanism: concrete saturated with water expands as the water freezes, and each freeze-thaw cycle adds stress. Deicing chemicals make it worse by keeping the surface wetter and adding freeze-thaw cycles. Entrained air, the tiny bubbles in good exterior concrete, gives the ice room to expand. Concrete with too little air, or a weak, porous surface, scales.
The salt you choose matters. The Iowa State brief says calcium chloride and magnesium chloride are the more aggressive deicers for concrete. NRMCA says calcium chloride and sodium chloride (rock salt) are acceptable in moderate amounts, but never to use ammonium sulfate, ammonium nitrate or magnesium-based salts, which attack concrete. It also says to hose salt residue off driveways and garage slabs when conditions allow, and that poor drainage leaving salty water standing on the slab speeds up damage.
When it is spalling
Spalling that follows corrosion is a different problem. When steel inside the slab rusts, the rust takes up more space than the steel and pushes the concrete cover off. ACI’s repair bulletin lists corrosion of embedded steel, freeze-thaw and chemical attack as the common causes of spalls in horizontal surfaces, and says an engineer should evaluate the damage and set out a repair plan first.
For reference, the ACI field guide describes a professional procedure along these lines:
- Sound the slab to find delaminated areas, mark simple shapes, and saw-cut the edge no deeper than the cover over the steel.
- Remove the unsound concrete. If a bar is corroded, remove the concrete around it until a hand can pass under it, with about 3/4 inch (20 mm) clearance.
- If a corroded bar has lost cross-section, bring in a structural engineer.
- Clean the steel and concrete with high-pressure water at 3,000 psi or more, or by abrasive blasting, then bring the concrete to a damp surface with no standing water before placing the repair.
- For ready-mixed repair concrete, ACI says a water-to-cement ratio of no more than 0.40 and a strength above the original and at least 4,000 psi, cured under wet burlap and plastic for at least 7 days, or sealed with a curing compound.
That is an engineered repair. A small spall on a driveway or garage slab with no steel showing is a lighter job, but the principles carry over: cut or chip back to sound concrete, clean thoroughly, and match the repair to the depth.
How to fix scaled or flaking concrete
NRMCA says light to moderately scaled surfaces can be repaired, but the repair is only as strong as the concrete underneath. Prepare the surface to remove everything unsound: hammer and chisel, sandblasting, a high-pressure washer or a jackhammer. The surface must be sound and free of dirt, oil and paint. The prepared surface can then take a thin bonded overlay, such as a Portland cement resurfacing, a latex-modified resurfacing or a polymer-modified cementitious repair mortar. NRMCA also warns that repair material will not match the color or character of the old concrete, and that heavily scaled slabs with progressing damage may not be worth repairing.
The Iowa State brief gives the options short and plain: do nothing and monitor if the damage is not progressing, grind off a thin layer, or apply a penetrating sealer that has to be reapplied periodically. For a thin overlay on a worn but sound slab, see our concrete resurfacer guide, which lists the layer limits and cure times from the makers’ sheets.
For a localized, flat spall with no steel showing, a pourable patch is one option. Rust-Oleum Pourable Concrete Patch is a self-leveling patch you mix with water and pour. It can be applied up to 4 inches deep in one pass, takes foot traffic in about an hour and vehicle traffic in as little as 3 hours, and sets in temperatures as low as 40 degrees Fahrenheit. Mix it at 4 ounces of cold water per pound of powder and use it within about 10 minutes. Those figures come from the Rust-Oleum data sheet I read for our resurfacer guide. Because it self-levels, it suits flat horizontal surfaces only, and it is not a substitute for the structural repair ACI describes if rusted steel is involved. I have not re-checked its Amazon listing today, so confirm stock yourself. Check price on Amazon: Rust-Oleum Pourable Concrete Patch. This is an affiliate link (see our disclosure for details).
Will concrete sealer stop spalling?
A sealer can slow some of it, but it cannot fix a weak surface or reverse rust that has started. NRMCA recommends a breathable silane or siloxane sealer or water repellent made for concrete slabs, applied when the concrete is reasonably dry, and suggests late summer after a few dry days. The Iowa State brief says sealants slow damage where water entry is the problem and need to be reapplied. For popouts, it says there is no way to mitigate them, although surface sealants may slow the rate of water penetration.
One product with a data sheet I have read is Foundation Armor SX5000, a solvent-based silane-siloxane water repellent. Its sheet lists 100 to 200 square feet per gallon on concrete, depending on porosity and texture, with two coats, and says it does not keep water out of cracks. Our driveway sealer guide has the full application limits. I have not re-checked its listing today. Check price on Amazon: Foundation Armor SX5000. This is an affiliate link (see our disclosure for details).
If you are replacing the slab
NRMCA’s guidance for new exterior slabs that will see freezing and deicers: order air-entrained concrete with a specified strength of 4,000 psi, about 6 percent total air for 3/4 or 1 inch stone, a slump of 3 to 5 inches with no water added at the site, finish only after the bleed water has gone, avoid steel troweling, cure it properly, and keep deicers off it in the first winter. A broom finish is enough for most exterior surfaces.
When to call a pro
Call someone if you see rusted steel, deep spalls, damage on steps or balconies where a failure could injure someone, or large areas that sound hollow. If a corroded bar has lost steel, ACI says to involve a structural engineer. For driveways, patios and garage floors you can find a local concrete contractor through Angi. This is an affiliate link (see our disclosure for details). For foundation walls, Angi’s foundation pros are one way to find one. This is an affiliate link (see our disclosure for details).
If the cause is cracks letting water in rather than surface damage, start with our concrete crack filler guide.
Sources: National Ready Mixed Concrete Association, Concrete in Practice CIP 1 (Dusting), CIP 2 (Scaling) and CIP 20 (Delamination of Troweled Concrete Surfaces); American Concrete Institute, RAP Bulletin 7, Spall Repair of Horizontal Concrete Surfaces (reapproved 2010); National Concrete Pavement Technology Center, Iowa State University, MAP Brief Summer 2023, Revisiting Concrete Scaling; Rust-Oleum Pourable Concrete Patch and Foundation Armor SX5000 data sheets as read for our earlier guides. The NRMCA and ACI documents were read on 13 November 2026. The Iowa State brief is about concrete pavements, so I applied its descriptions to home slabs with that in mind. The advice to document new-slab damage for the contractor is my own suggestion. I did not test any concrete.
Etienne Basson maintains and repairs his own home, and writes practical guides on choosing the right materials and products for repair and finishing jobs: fillers, sealants, adhesives, and similar. He focuses on what actually works for a specific job, not just a spec sheet.