Concrete · Service

Concrete repair, and reading what the crack is telling you

A tight shrinkage crack and a crack with one side sitting lower than the other are two entirely different problems. One is sealing work. The other means the ground moved.

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In short

What is concrete repair?

Concrete repair covers sealing and filling cracks, patching spalled or broken edges, and resurfacing a slab whose top layer has failed. Whether any of it is worth doing depends on one question: is the concrete cracked, or is the concrete fine and the ground beneath it the thing that has moved? Sealing work fixes the first. Only lifting or rebuilding addresses the second.

Triggers

Signs you need concrete repair

Cracks are wide enough to hold water, grit or weeds, or wide enough to catch a shoe
The surface is flaking, scaling or shedding sand — most visible after winters with de-icing salt
Edges have crumbled away, particularly along a driveway apron or a step nosing
One side of a crack sits lower than the other, so the slab has moved as well as split
Reinforcing steel is visible and rusting where the concrete around it has broken away
Joints have opened up and the sealant in them has perished or disappeared
A step or stoop has a broken corner or a chipped nosing that is now a trip hazard

Seeing something not on this list? Browse concrete problems by symptom →

The job

How concrete repair actually works

Reading the crack

The assessment starts with whether the two sides of the crack are still in the same plane. Level across, tight and stable means shrinkage or thermal movement. A vertical step across the crack, or a crack that keeps widening, means the support underneath has changed.

Watch for: A repair quoted straight from a photo. Whether one side has dropped is something you establish by putting a straightedge across it, and it changes the entire recommendation.
Finding the water

Almost all concrete deterioration is water-driven — water entering cracks and freezing, water washing base material out from under a slab, water pooling because the fall is wrong. The repair scope should include where the water is coming from.

Watch for: A downspout discharging at the edge of the slab being repaired. It is astonishingly common, it is cheap to extend, and leaving it means repeating the repair.
Preparing the crack or defect

Cracks are cleaned out and often widened into a consistent profile so a sealant or repair mortar has something to grip. Spalled areas are cut back to sound concrete with square edges rather than feathered to nothing.

Watch for: Patch material applied over a feathered edge or a dusty surface. Feathered edges break away, and a bond onto dust is no bond at all. Square-cut edges are the visible sign of a repair meant to last.
Filling and sealing

Moving joints get a flexible sealant that can accommodate the movement. Static cracks get a rigid repair mortar or a resin. Choosing a rigid product for a moving joint is the classic mistake.

Watch for: A rigid patch used across a control joint. The joint exists to move. Filling it rigidly simply relocates the crack a few inches away, into concrete that was previously fine.
Resurfacing, where the surface has failed but the slab has not

A thin overlay can restore a spalled or scaled surface, provided the slab underneath is structurally sound, properly prepared and the overlay is bonded to it.

Watch for: Resurfacing used to hide structural cracking. The overlay is thin and it will crack directly above any crack it is covering, usually within the first season — and it will have cost real money to get there.
Sealing joints and protecting the result

Open joints are resealed and, in freeze-thaw climates, the slab is often sealed to slow water and salt penetration into the surface.

Watch for: Sealing applied over a still-damp repair or too soon after a cementitious patch. It traps moisture in the material you just installed.

Money

What does concrete repair cost?

Crack sealing and small patching are among the least expensive concrete services and are usually a single visit. Resurfacing costs considerably more, and once a repair estimate approaches roughly half the price of replacing the slab, replacement is usually the better purchase. See the Cost Guide.

See the full concrete repair cost guide — by material, size and region →

Straight answer

When concrete repair is the wrong call

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

One side of the crack has dropped. That is a settlement problem, not a crack problem. Filling it produces a filled crack with a step still in it. Lifting the slab, or rebuilding the base, is the actual repair.
The slab is cracked in a network across most of its area. Widespread map cracking generally means the concrete itself or the base is failing broadly. Chasing individual cracks across a failed slab costs more over a few years than replacement would have.
The surface is deteriorating and you want resurfacing to make it permanent. An overlay restores appearance and some protection, but it does not repair concrete underneath it. On a slab that is scaling because the mix or the finishing was wrong, the overlay is a delay, not a cure.
You are repairing to sell and expecting it to look new. Repairs to concrete are visible. Colour, texture and age will not match, and a patchwork driveway can read worse to a buyer than an honest, evenly weathered one.
Reinforcement is corroding through much of the slab. Steel expands as it rusts and pushes the concrete apart from the inside. Patching over it puts a cover on a process that continues underneath.
The slab was under-specified for what you are doing on it. A patio slab used as a parking pad will keep failing. Repairing it repeatedly costs more than pouring the right slab once.

Your options

Types of concrete repair

Repair vs replace

The comparison this page keeps running into, worked through with the numbers.

Diagnose by symptom

Cracked driveways, spalling, scaling and failed patio slabs.

Sealers and joint materials

What sealers do, what control joints are for, and which materials suit which movement.

Compare concrete options side by side →

Straight answer

Can I do this myself?

Reasonable to DIY

Sealing tight, stable cracks with a purpose-made flexible crack sealant
Re-sealing open control joints, which is genuinely one of the highest-value maintenance jobs a homeowner can do
Applying a concrete sealer to a sound, cured slab
Extending a downspout so it stops discharging beside the slab — often the actual fix
Small cosmetic patches to a step edge, accepting that the colour will not match

Call a licensed pro

Any crack where one side sits lower than the other
Resurfacing, which needs proper surface preparation and a very short working time once mixed
Anything with exposed, corroding reinforcement
Repairs to steps, stoops or anything carrying load
Any repair involving cutting or grinding concrete, because of silica dust exposure

Before you sign

What to check when hiring for concrete repair

Is either side of this crack lower than the other, and did you check with a straightedge?

The question that decides whether you need sealing or lifting. It takes ten seconds and it changes everything.
What is letting water in, and is fixing that in the scope?

Drainage is the cause of most of this damage and the cheapest part of most of these repairs.
Are you cutting back to sound concrete with square edges?

Feathered patch edges break away. Square cuts are the visible marker of a repair that is meant to hold.
Is this repair rigid or flexible, and does that match how this joint moves?

Rigid material in a moving joint just moves the crack next door.
Will this match the existing concrete, honestly?

It will not, entirely. You want a realistic answer so you can decide whether appearance changes the repair-or-replace call.
At what point would you tell me to replace instead?

A repair contractor with a threshold in mind is giving you advice. One without is giving you a quote.

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Local pros

Concrete Repair near you

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Related work

Often done at the same time

Concrete Leveling

When the slab has dropped rather than cracked

Concrete Installation

When repair stops being worthwhile

Driveway Installation

The most commonly repaired slab of all

Concrete Demolition

Removing what cannot be saved

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FAQ

Concrete Repair — questions people ask

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Which concrete cracks actually matter?

The ones with a height difference across them, the ones that keep getting wider, and the ones deep and open enough to take water into the base in a freezing climate. Hairline shrinkage cracks that are level across and stable are cosmetic, and sealing them is maintenance rather than repair. A crack that has moved is telling you about the ground, not the concrete.

Does concrete resurfacing work?

On a structurally sound slab with a failed surface, yes — a properly prepared and bonded overlay restores appearance and adds protection. On a slab with structural cracks or a failing base, no. The overlay is thin, it reflects whatever is under it, and a crack beneath will reappear through the new surface within a season or two.

Why is my concrete flaking and peeling?

Usually a weak surface layer combined with freeze-thaw cycling and de-icing salts. That weak layer typically originates on pour day — too much water in the mix, or finishing worked while bleed water was still standing. It can be resurfaced, but it cannot be repaired back into strong concrete, because the weakness is the top layer itself.

Should control joints be filled?

With a flexible joint sealant, yes — it keeps water and grit out while still letting the joint do its job. With rigid patching material, no. The joint exists specifically so that movement concentrates there. Lock it and the movement finds somewhere else to go, which is a new crack in previously sound concrete.

When is it cheaper to replace than repair?

A useful rule of thumb is that once repair costs approach roughly half of replacement, replacement is usually the better purchase — you get a full service life instead of an extension. Widespread cracking, a failing base, or corroding reinforcement all push the calculation toward replacement regardless of the raw numbers.

Will a repair match the rest of the slab?

Not closely. New concrete and repair mortars cure to a different colour than aged concrete, texture is difficult to reproduce, and the patch will weather differently from here on. It generally becomes less obvious over years but never disappears. Where appearance is the point of the job, that fact should be part of the repair-or-replace decision rather than a surprise afterwards.