Concrete floor crack repair: crack types, repair methods and costs

Concrete floor crack repair starts with diagnosing the crack. Hairline cracks under about 0.2 mm can often be left, dormant cracks up to about 3 mm are filled or injected with epoxy or PU resin, wider cracks and broken edges are cut out and filled with EN 1504-3 repair mortar, and settlement or structural cracks need their cause fixed first.

The overview table below links each crack type to its repair. Costs run from a few tens to a few hundred euros per linear metre of injected crack to an indicative €50 to €500 per m² for mortar repairs (2026, Dutch price level). Lasting concrete repair also means that the repair material itself must not shrink and crack, which is where fibres come in.

Which repair for which crack? Overview by crack type and width

Use the table to match what you see to a repair; widths are indicative and the diagnosis sections below explain each type.

Cracks in a concrete floor: which type are you looking at?

Anyone who fills a crack straight away without knowing the cause often ends up repairing twice. Cracked concrete, in everyday speech often called cracked cement, tells you a good deal about its cause if you read it properly. A floor crack that has a step between its edges points in a very different direction from a fine network that appeared in the first week. Look at five things before choosing a repair:

• Pattern and direction: short diagonal or irregular cracks, a fine map-like network, straight cracks across the middle of a bay, or cracks running from corners, columns and pits.

• Width: measure it with a crack width gauge or comparator card, or with a feeler gauge for wider cracks, and note where along the crack you measured.

• A step between the edges: any height difference means the slab has moved, which points to settlement or overloading.

• Age of the floor: cracks in the first day are plastic shrinkage; cracks that appear over the following weeks and months are usually drying shrinkage.

• Rust staining: brown streaks, or cracks that follow the line of the reinforcement, point to corrosion rather than shrinkage.

Also check whether the crack follows a sawn joint. Contraction joints are planned cracks: the saw cut makes the slab crack in a straight line where the designer wants it, so a crack below a saw cut is the joint doing its job, not a defect. Beyond that, cracks in a concrete floor fall broadly into four categories, each with its own cause and its own repair approach.

Shrinkage cracks

By far the most common damage. Plastic shrinkage cracks form in the first 24 hours after pouring, when the surface dries out faster than the bleed water can replenish it; they are 0.1 mm to a few millimetres wide and often run diagonally or in an irregular pattern. Drying shrinkage follows in the weeks to months after that (hardening concrete typically shrinks 0.4 to 0.6 mm per metre) and concentrates at weak spots or oversized joint bays. Crazing, a fine network of surface cracks caused by rapid surface drying or over-trowelling, is a cosmetic variant that stays in the surface layer. How these mechanisms work and how to prevent them is covered in preventing shrinkage cracks in concrete.

The key point for the repairer: once the slab has dried out, shrinkage cracks are dormant. They no longer move under load and can therefore be filled or injected successfully. Shrinkage crack repair is covered under method 1 below.

Settlement cracks

If the subgrade settles unevenly, the floor follows and cracks. Typical causes are poorly compacted or organic fill, a pipe trench, a leaking drain washing out the sub-base, and shrinkable clay drying out, often near trees whose roots draw moisture from the ground. Settlement cracks are often wider at one end, run through the full floor thickness and are regularly accompanied by a height difference between the crack edges, known as lipping. As long as the settlement continues, the crack is live. Stabilise the subgrade first (for example by injection beneath the slab) and only then repair the crack; otherwise the repair will simply crack open again right next to it. The full sequence is set out in the section on concrete floor settlement repairs below.

Structural cracks

Cracks caused by overloading (a heavier forklift or racking than the floor was designed for, a point load in an unexpected place) can be recognised by their location: at the load point, often in a regular pattern or perpendicular to the span direction. Here, crack repair alone is not enough: a structural engineer must first assess whether the floor can carry the load at all. Neither fibres nor mortar replace that calculation.

Structural concrete crack repair means restoring the bond or load path across the crack, by injection, stitching or strengthening. It is only carried out once the engineer has confirmed that the cause has been removed. Methods 2 and 5 below describe how it is done.

Concrete spalling: a different story

If you see rust-brown stains, cracks running parallel to the reinforcement or delaminating slabs, the cause is not shrinkage or settlement but corrosion of the reinforcing steel: rust occupies up to six times the volume of the original steel and bursts the cover apart. That damage pattern requires a fundamentally different approach (removing deteriorated concrete to behind the reinforcement, de-rusting the steel, reinstating to EN 1504), which we cover separately in concrete spalling: causes, recognising and repairing it.

Live or dormant? How to monitor a crack

This is the key repair decision. A dormant crack no longer moves, so it can be filled with a rigid material such as epoxy resin or repair mortar. A live crack opens and closes with temperature or load, or keeps growing. A rigid repair in a live crack will simply crack again, so either the cause is removed first or the repair has to be flexible. Checking which you have takes patience rather than equipment:

• Mark both ends of the crack with a pencil line and the date.

• Measure the width at a few fixed, marked points with a crack width gauge and write the readings down.

• For a more precise record, fix a tell-tale (a small two-part gauge with a scale) across the crack.

• Read the marks over several months, ideally across a change of season, because temperature swings open and close live cracks. Practice guides often cite around six months; treat that as indicative rather than a rule.

A crack that grows in length, gets wider or develops a new step is live. A crack that stays the same throughout that period is dormant and can be repaired rigidly.

Are cracks in a concrete floor normal, or serious?

Fine hairline shrinkage cracks are normal in a new concrete floor, and indoors they are usually cosmetic. They become serious when moisture, chlorides, liquid-tightness requirements or traffic on the edges come into play, or when the crack grows or shows a step. The rule of thumb per situation:

• Fine shrinkage crack (up to about 0.2 mm) in a dry indoor floor: usually harmless and mainly aesthetic. Monitoring is sufficient.

• Crack in a floor exposed to moisture, chloride or frost: harmful, because the crack gives water and de-icing salts a direct route to the reinforcement, with corrosion of the reinforcing steel as the result. Repair.

• Crack in a liquid-tight floor (agricultural, wash bay, environmental permit): every through crack counts as a leak. Repair it, and be able to show the floor is liquid-tight again.

• Crack along edges under forklift traffic: the edges crumble at an accelerated rate under wheel loading, and small damage grows. Repair before the break-up begins.

• Live crack (settlement, overloading) or a height difference between the edges: always have the cause assessed first.

For a more precise assessment, crack width is the criterion the standard also uses. EN 1992-1-1 (Eurocode 2; BS EN 1992-1-1 in the UK) recommends a maximum design crack width of 0.3 to 0.4 mm for reinforced concrete, depending on the exposure class (0.2 mm for prestressed members): the more aggressive the environment (moisture, chlorides), the stricter the requirement. If you measure more than about 0.3 mm with a crack width gauge or loupe, or the crack is demonstrably growing, assessment and repair are advisable.

How to repair a crack in a concrete floor: step by step

Whichever method suits the crack, the work follows the same eight steps. Skipping the first two is the most common reason why repaired cracks come back.

• 1. Find the cause and confirm the crack is dormant. A repair only lasts once the cause has gone; if in doubt, monitor the crack first.

• 2. Measure and record. Note the width and length and any step between the edges, and photograph the crack with a ruler or gauge alongside.

• 3. Prepare the crack. Remove loose material. Do not widen cracks you are going to gravity-fill or inject. For a mortar repair, cut out with a diamond blade to a groove with square edges; for routing and sealing, cut a sealant groove along the crack.

• 4. Clean, then dry or pre-wet. Vacuum out all dust. Resins need a dry, dust-free crack; cement-based mortars need a pre-wetted, saturated surface-dry substrate or the primer the manufacturer specifies.

• 5. Fill with the material that matches the width: a low-viscosity resin, an injection resin, a repair mortar or a flexible sealant (see the six methods below).

• 6. Finish flush. Overfill slightly and scrape or grind level after curing. If a coating follows, broadcast dry sand onto the fresh resin for grip.

• 7. Cure and protect according to the product data sheet before allowing foot traffic, vehicles or a coating.

• 8. Check again after a few months. A filled crack that reopens is live and needs a flexible repair or a structural assessment.

Fine, dormant cracks in a non-structural floor are DIY work. Pressure injection, crack stitching, settlement and structural cracks are specialist work. A cracked screed is repaired in much the same way, but it is a different layer with causes of its own; see cracks in a sand cement screed.

Concrete floor crack repair: six methods compared

Once the cause is known and removed, the damage pattern determines the method. ACI PRC-224.1-07 (Causes, Evaluation, and Repair of Cracks in Concrete Structures) lists these among its principal repair techniques; for floors, six matter in practice. They are described below from least to most invasive.

1. Shrinkage crack repair: gravity filling fine cracks

For hairline and fine dormant cracks in a horizontal slab (indicatively up to about 1 to 2 mm wide), gravity filling is the simplest repair. A very low-viscosity resin (epoxy, methacrylate or polyurethane) is poured or brushed over the crack and runs in by gravity and capillary action. The excess is then scraped off, and dry sand is broadcast onto the fresh resin if a coating is to follow.

It is the cheapest and least invasive method, and a typical step before coating a floor or in floors exposed to moisture, where sealing the crack keeps water out. Its limits: it does not restore strength in wider cracks, it is not suitable for live cracks, and the repair line stays visible.

2. Crack injection with epoxy or PU resin

For fine, dormant cracks (indicatively 0.1 to 3 mm), injection is the standard, and structural concrete crack repair usually starts with epoxy injection too. Packers (injection ports) are drilled in or bonded on along the crack at intervals, and the crack surface between them is sealed so that the resin cannot escape. The resin is then injected at low pressure, starting at the lowest packer (on a level floor, at one end of the crack) and moving on to the next packer as soon as resin appears there, until the crack is completely filled. After curing, the packers are removed.

The choice of resin follows the situation. Epoxy resin bonds the crack faces with structural strength restoration, so the floor becomes one whole again; it suits dry, stable cracks. PU resin remains elastic and foams up on contact with water, so it also seals leaking or slightly damp cracks; it does not restore strength. Injection is minimally invasive: no demolition work, and the floor largely stays in use. The drawback: the repaired crack remains visible as a dark line, which is a nuisance in a power-floated exposed floor.

3. Routing and sealing live cracks and joints

For cracks that keep moving and for failed joints, a rigid filler is pointless: it cracks again beside or through the repair. Instead, the crack is opened up with a saw or router into a sealant groove (indicatively at least about 6 mm wide, following ACI guidance), cleaned, fitted with a bond breaker at the bottom and filled with a flexible sealant such as polyurethane, polysulphide or MS polymer. In effect, the crack is turned into a joint.

In industrial floors with hard-wheeled forklift traffic, a semi-rigid filler takes the place of the flexible sealant, so that the joint edges stay supported and do not break away under the wheels. Routing and sealing does not restore any strength, and the seal needs maintenance over time. For the design side, see our article on joints and cracks in industrial floors.

4. Cutting out and filling with repair mortar (EN 1504-3)

Wider cracks, crumbled joint edges, holes and damaged surfaces are mechanically cut or milled out to sound concrete, vacuumed clean of dust, given a bonding primer and filled with a repair mortar. Structural concrete repair to EN 1504-3 uses mortars of class R3 or R4; for non-structural cosmetic work, R1 or R2 suffices.

An important detail: good repair mortars are themselves often polymer-modified and fibre reinforced. Micro fibres in the mortar limit the shrinkage of the repair, which is precisely the mechanism through which the original damage arose. If you mix your own mortar for larger repair work, you can include micro fibres in repair mortars to limit plastic shrinkage cracking in the new layer.

5. Crack stitching: reinforcing across a structural crack

When a crack has to carry tension again, filling it is not enough: reinforcement has to cross it. With crack stitching, slots are cut across the crack at intervals and steel bars (deformed bars or stainless helical bars) are bonded into them with epoxy or a resin grout, usually after the crack itself has been injected. The stitches are given varying lengths and spacing, so that the stress is not transferred along a single line where the next crack would form. This restores tensile capacity across the crack, but only on an engineer's design.

ACI guidance adds a caveat: stitching an active crack stiffens the slab locally and can simply move the cracking elsewhere, so the cause has to be removed first. Heavier strengthening, such as additional reinforcement or bonded carbon fibre strips, is engineer territory and beyond the scope of this article.

6. Overlaying with a fibre reinforced topping

If the damage is not local but spread across the entire surface (map cracking across the floor, a worn-out top layer, countless repair patches), repairing crack by crack is a losing battle. Overlaying is then the logical route: the existing floor is milled or blasted for bonding, and a new structural topping of (fibre) concrete is laid over it.

At limited layer thicknesses, traditional mesh reinforcement is difficult to position with sufficient cover. A fibre reinforced overlay of a worn floor with structural macro fibres (dosage indicatively 2 to 6 kg/m³, depending on layer thickness and loading) does not have that problem, because the reinforcement is distributed homogeneously through the whole of the thin layer. The same technique also exists on top of worn asphalt: white topping with fibre concrete. With any overlay, watch two points: the bond with the substrate and the residual load-bearing capacity of the existing structure. Both determine whether the new layer can do its job.

Repairing floor cracks before tiling, coating or a new floor finish

A crack in the slab does not stay hidden under a new finish: it reflects through tiles and resin coatings, and telegraphs through thin vinyl. How to deal with it depends on whether the crack is still moving.

• Dormant cracks: fill them rigidly with resin. Under tiles, also bridge the crack with a crack-isolation or uncoupling membrane, following the instructions of the tile system.

• Live cracks and joints: carry them through the finish as a movement joint. Never tile or coat rigidly over a moving crack; the finish will crack along the same line.

• Resin coatings: pre-treat the cracks with resin and let the repair cure fully before the coating goes on.

Concrete floor settlement repairs: stabilise first, then repair the crack

A settled floor shows more than a crack. Typical signs are a step at the crack (lipping), a floor that slopes as you walk across it, a gap opening under the skirting boards, doors that start to bind, and a hollow sound when you tap the slab, which points to a void underneath. The usual causes are poorly compacted or organic fill, a sub-base washed out by a leaking drain, and shrinkable clay drying out near trees. The repair follows a fixed order:

• 1. Find and stop the cause. Have the drains surveyed, deal with leaks and standing water, and assess the influence of trees.

• 2. Monitor until the movement has stopped, using the marks and gauges described above.

• 3. Lift or void-fill the slab. Expanding resin or cementitious grout is injected beneath the slab through small drilled holes (slabjacking). This fills the voids and can bring the floor back to level without breaking it out.

• 4. Break out and recast where lifting will not work, for instance when the slab is broken up or the fill is unsuitable. The new floor goes on a properly compacted sub-base, for example as a fibre reinforced slab; see how thick a concrete floor should be.

• 5. Only then repair the crack, by injection or with mortar, or overlay the floor.

Slab lifting has its limits: the slab itself must be sound, the lifting can open new cracks, and the floor will settle again if the ground below remains poorly compacted. Nor does lifting close shrinkage cracks: hairline cracks in a concrete patio without a step between the edges are no reason to raise the slab. If the settlement is ongoing or the walls are cracking as well, it is no longer a floor repair: bring in a structural engineer, as underpinning may be needed.

What do concrete repairs cost? Indicative prices 2026

The costs of concrete repair vary widely with extent, accessibility and whether the repair needs to be structural. The figures below are indicative 2026 prices at Dutch price level. Prices in the UK and other markets differ, so compare local quotes.

• Crack injection (epoxy/PU): indicatively a few tens to a few hundred euros per linear metre of crack, depending on crack width, slab thickness and length.

• Small, non-structural mortar repair (localised patches, easily accessible): €50 to €150 per m² of repair area.

• Structural repair to EN 1504-3 (class R3/R4, including preparation): €150 to €500 per m².

• Gravity filling, routing and sealing, and crack stitching: usually priced per linear metre or per stitch after an inspection; settlement repairs (void filling, slab lifting) are priced per project after a survey.

• Overlaying with a new fibre concrete layer: strongly dependent on layer thickness and area. Per square metre it is often cheaper than large-scale localised repair, precisely because the work happens in one continuous operation.

• Diagnosis beforehand (crack width measurement, core drilling, cover measurement): a few hundred euros, and almost always recouped because you do not repair too much or the wrong thing.

For comparison, prevention is indicatively a small fraction of this: micro fibres added to the fresh concrete against plastic shrinkage cracks cost far less than a later crack repair.

Repair or replace a concrete floor?

Sometimes continuing to repair no longer makes sense. Three signals that renovating a concrete floor (overlaying or replacing it) is wiser than yet more localised repair:

• Widespread damage: more than roughly a quarter of the surface shows cracks, delamination or wear. The sum of localised repairs then approaches the price of a new layer, with a patchwork as the result.

• Recurring damage: earlier repairs crack again, because the underlying cause (oversized joint bays, missing shrinkage reinforcement, weak subgrade) was never removed.

• Changed use: the floor must carry heavier loads, become liquid-tight or be flatter than the original ever could. A new, correctly dimensioned layer is then the only route that also meets the requirements.

With complete replacement, the same applies as with overlaying: this is the moment to make the new floor better than the old one, with the right joint layout, curing and fibre reinforcement from day one.

Concrete crack reinforcement: fibres in the repair and the new layer

Concrete crack reinforcement can mean two different things. Reinforcing an existing crack so that it carries tension again is stitching (method 5). Reinforcement against the next crack goes into the repair material or the new layer, and that is where fibres come in. No reinforcement prevents all cracking: it controls the width and spacing of cracks, which is what keeps them harmless. The mechanism is explained in how fibre reinforcement controls cracking.

The bitter lesson of many repaired floors: the repair itself is also young concrete, and therefore cracks for exactly the same reasons as the original. Anyone who repairs or overlays a floor without controlling the shrinkage lays the foundation for the next round of repairs. Limiting shrinkage cracks in the repair with fibre reinforcement tackles that at source, on three levels.

• Repair mortar and screed: PP micro fibres absorb the tensile stresses in the plastic phase, so the new layer is far less prone to plastic shrinkage cracking. Promicro (0.6 to 1.0 kg/m³) suits concrete floors, precast and shotcrete; Profib (0.9 to 1.0 kg/m³) suits sand-cement screed.

• Overlay and new floor: structural macro fibres such as TwistR (100% virgin polypropylene, non-corrosive, 2.0 to 6.0 kg/m³) reinforce the full layer thickness without fixing work. In moisture-laden floors they also rule out the corrosion failure path of a thin reinforcement mesh.

• Combination: micro fibre against the plastic shrinkage of the first 24 hours, macro fibre or mesh for the months after. For structural work, the dimensioning belongs with the structural engineer.

More background on fibre types, dosages and standards (EN 14889) can be found in our knowledge centre on fibre reinforced concrete.

From damage pattern to repair advice

Unsure which crack type you are looking at, or which fibre suits your repair mortar or overlay? Send a few photos and the dimensions with a quotation request. Our specialists advise free of charge on method, fibre choice and dosage, and calculate the required quantities for you straight away. Planning a new floor with macro fibres? The savings calculator compares the cost of TwistR fibre reinforcement with traditional steel reinforcement per m².