Epoxy Injection Resin for Concrete Crack Repair
Low-viscosity two-component epoxy that travels into cracks from 0.05 mm and bonds the crack faces back together.
Specifications at a glance
FSE 523 is a two-component, solvent-free epoxy injection resin for restoring structural continuity across cracked concrete, masonry and timber. At a mixed viscosity of ≤ 300 mPa·s it travels into cracks as narrow as 0.05 mm under low-pressure injection, or 0.1 mm by gravity, and cures with ≤ 0.3% linear shrinkage so the crack faces stay in contact. Bond to concrete is ≥ 2.5 MPa dry and ≥ 1.8 MPa wet, both failing in the concrete rather than in the bond line (ASTM C882) — the repaired joint is stronger than the material around it.
| Property | Value |
|---|---|
| Model | FSE 523 |
| Type | Two-component, solvent-free epoxy injection resin |
| Mix Ratio | A : B = 2 : 1 by weight |
| Appearance | A: grey/white; B: grey/white; Mixed: grey/white |
| Mixed Viscosity | ≤ 300 mPa·s |
| Pot Life | 150 min (10°C) / 40 min (23°C) / 30 min (30°C) |
| Min. Crack Width | 0.05 mm (pressure) / 0.1 mm (gravity) |
| Tensile Strength | ≥ 25 MPa (ASTM D638) |
| Elastic Modulus | ≥ 1.5 GPa (ASTM D638) |
| Elongation at Break | ≥ 1.8% (ASTM D638) |
| Flexural Strength | ≥ 30 MPa (ASTM D790) |
| Compressive Strength | ≥ 80 MPa (ASTM D695) |
| Bond — Dry Concrete | ≥ 2.5 MPa, concrete failure (ASTM C882) |
| Bond — Wet Concrete | ≥ 1.8 MPa, concrete failure (ASTM C882) |
| Steel-to-Steel Shear | ≥ 25 MPa (ASTM D1002) |
| Linear Shrinkage | ≤ 0.3% |
| Density (Cured) | 1.1 ± 0.1 g/cm³ |
| Service Temperature | -5°C to +40°C |
| Packaging | 20 kg (A) + 10 kg (B) per kit; injection cartridges available |
| Shelf Life | 18 months (unopened, +4 to +32°C) |
Where It Is Used
Bridges, viaducts and parking decks
Flexural and shrinkage cracks in decks, beams and diaphragms, where sealing the crack keeps de-icing salt and standing water off the reinforcement.
Industrial floors and plant structures
Cracked slabs, machine bases and frames, restored before traffic and vibration open them further.
Basements, tanks and retaining walls
Cracks that leak. Filling the crack cuts the water path, and the cured resin resists water, acids, alkalis and salt.
Before bonded strengthening
Restoring load transfer across dormant cracks, so a carbon fabric or plate system bonds to a member that behaves as one piece rather than two.
Masonry and older structures
Concrete, masonry, stone and timber. Low viscosity matters most here, where cracks are irregular and often finer inside than they look on the surface.
Hot-climate sites
Service range −5 °C to +40 °C. Above 30 °C pot life drops to about 30 minutes, so batches get smaller and the work moves to the cooler hours.
Selection Guide
| Crack width | What to do | Watch out for |
|---|---|---|
| Below 0.05 mm | Not injectable. Seal or coat the surface instead. | Below the width at which resin can reliably travel the length of the crack, even under pressure. |
| 0.05 – 0.1 mm | Low-pressure injection only. Ports at 200 mm, crack face sealed with FSE 502. | Gravity filling will not enter a crack this fine. Inject slowly and give the resin time to travel. |
| 0.1 – 0.5 mm | Low-pressure injection on vertical and overhead work; gravity fill on horizontal slabs and decks. | The everyday case — most structural cracks land in this band. |
| 0.5 – 2 mm | Either method. Port spacing can go out to 300 mm. | Volume climbs quickly with width. Check the consumption table before you size the order. |
| Above 2 mm | Gravity fill, or rout the crack out and fill it. | At this width, ask why it opened before you fill it. A wide crack is usually a symptom of something else. |
| Any width, still moving | Do not inject. Use a flexible sealant. | Cured epoxy is rigid and stronger than the concrete, so an active crack re-opens beside the repair instead of through it. |
| Product | What it is | You need it when |
|---|---|---|
| FSE 523 | Injection resin · two-part, 2 : 1 by weight · ≤ 300 mPa·s | Always. This is the resin that goes into the crack and bonds the faces back together. |
| FSE 502 | Surface sealing paste · two-part, 2 : 1 by weight · trowel grade | On every pressure-injection job. It seals the crack face and holds the port bases, so the resin goes into the crack instead of out along it. Touch-dry in about 1.5 h at 23 °C — let it cure before you inject. |
| Injection ports | Manual low-pressure ports · clear barrel · 50 per box | On pressure work. The clear barrel is how you see resin arrive at the next port, which is how you know the section behind you is full. |
| Dispensing gun | Dual-component caulking gun for cartridges | Only if you take FSE 523 in cartridges. Kits are mixed in a pot and poured or pumped instead. |
Kits are 20 kg of Part A plus 10 kg of Part B; cartridges are available for small runs. Mix strictly 2 : 1 by weight — epoxy that is out of ratio does not cure to strength, it stays soft. Pot life is 150 min at 10 °C but 40 min at 23 °C and 30 min at 30 °C, so on a hot site mix small batches.
Injection restores load transfer across a crack that has stopped moving, and closes the path water and chloride take to the reinforcement. It does not add capacity to a member that was never strong enough. If the crack came from overload, insufficient reinforcement or foundation movement, that cause is the project engineer's to resolve first — injection is the last step, not the fix.
How Much Resin You Need
Resin volume by crack width and depth
| Crack width (mm) | 50 mm deep (mL/m) | 100 mm deep (mL/m) | 200 mm deep (mL/m) | 300 mm deep (mL/m) | 10 m run, 200 mm deep (mL) |
|---|---|---|---|---|---|
| 0.05 | 2.5 | 5 | 10 | 15 | 100 |
| 0.1 | 5 | 10 | 20 | 30 | 200 |
| 0.2 | 10 | 20 | 40 | 60 | 400 |
| 0.3 | 15 | 30 | 60 | 90 | 600 |
| 0.5 | 25 | 50 | 100 | 150 | 1000 |
| 1.0 | 50 | 100 | 200 | 300 | 2000 |
| 2.0 | 100 | 200 | 400 | 600 | 4000 |
Millilitres per linear metre = crack width in mm × crack depth in mm. A crack 0.2 mm wide through a 200 mm slab takes 40 mL for every metre of its length.
These are geometric volumes — what the crack would hold if it were a clean rectangular slot. Real cracks widen inside, branch, and lose resin at the ports and in the mixer nozzles, so order above the table. Even so the quantities are small: at 0.2 mm through 200 mm, one 30 kg kit holds roughly 680 m of crack in theory (cured density 1.1 g/cm³). Send us the crack length, width and element thickness and we will size the order with you rather than sell you a pallet you do not need.
Injection in Six Steps
Find out why it cracked
Before anything else, establish that the crack has stopped moving and that the member is not overloaded or under-reinforced. Injection restores continuity across a dormant crack; it is not a substitute for strengthening, and a crack that is still working needs a flexible sealant rather than resin.
Clean the crack
Wire-brush the crack and blow it out with oil- and water-free compressed air. It must be free of dust, laitance, oil and standing water. Resin will not bond through a dusty or oily crack face — the bond figures on the datasheet assume a clean one.
Set the ports
Fix injection ports along the crack at 200–300 mm centres — the closer spacing on fine cracks and thin sections. Start from the lowest point of a vertical crack; where a wall is cracked right through, port both faces.
Seal the crack face
Trowel FSE 502 over the crack between the ports and around each port base, and let it cure — about 1.5 h to touch-dry at 23 °C. This seal is what forces resin into the crack instead of out along the surface. Skipping it is the most common reason an injection never fills.
Inject from the bottom up
Fit the static mixer and dispense to waste until the colour runs uniform, then inject at the lowest port under slow, steady pressure. Stop when resin appears at the next port up, plug the port you were on, and move up. Working upward pushes the air out ahead of the resin. On horizontal cracks, gravity fill instead: vee-notch, clean with compressed air, and pour slowly until full.
Cure, then cut back
Leave it undisturbed. Application range is −5 °C to +35 °C, and full strength comes at 7 days at 23 °C. Once cured, grind off the ports and the FSE 502 seal and make the surface good.
Frequently Asked Questions
What is the narrowest crack you can inject?
0.05 mm under low-pressure injection, 0.1 mm by gravity. Both figures come from the FSE 523 datasheet and follow from the mixed viscosity, ≤ 300 mPa·s. Below 0.05 mm the resin cannot reliably travel the length of the crack, and a surface coating is a more honest answer than an injection that only fills the first few centimetres.
Can I inject a crack that is still moving?
No. Cured epoxy is rigid and stronger than the concrete around it, so a crack that is still working simply re-opens beside the repair. Movement from thermal cycling, live load or settlement calls for a flexible sealant. Establish that the crack is dormant first — by monitoring it over a period, or through an engineer's assessment.
Does injection make the member stronger?
It gives back what the crack took away: load transfer across the crack faces, and the barrier that keeps water and chloride off the reinforcement. It does not add capacity. Where an element has to carry more than it was designed for, injection is the preparation and external strengthening — bonded carbon fabric or plate — is the fix.
Does it work on damp concrete?
It bonds to damp concrete: ≥ 1.8 MPa wet against ≥ 2.5 MPa dry, both failing in the concrete rather than in the bond line (ASTM C882). What it will not do is displace standing or running water inside the crack. Blow the crack out and let it dry back before injecting.
Do I really need the surface sealing paste?
For pressure injection, yes. Without a seal the resin takes the easiest path, which is out along the face of the crack, and the crack never fills under pressure. Gravity filling of an open crack in a horizontal surface is the one case where you can work without it.
How much resin should I order?
Start from the consumption table above: millilitres per metre equals crack width in millimetres times crack depth in millimetres. Then add for branching and for what stays in the mixer nozzles. Send us the crack length, the width and the element thickness and we will work the quantity out with you.
Do you have a European Technical Assessment or an ICC-ES report for it?
No. FSE 523 ships against its own technical data sheet, with the property values tested to the ASTM methods named in the specification table on this page, plus a Mill Test Certificate and Certificate of Analysis for the batch. If your specification calls for a particular third-party approval, say so at enquiry stage and we will tell you plainly whether we can meet it.
Documents & Downloads
Two datasheets, not one
FSE 523 for the injection resin and FSE 502 for the surface sealing paste. Both carry the full property tables, pot life by temperature and the application procedure.
MTC + COA with every shipment
Every batch ships with a Mill Test Certificate and a Certificate of Analysis.
Request a Quote
Send the crack width, the length, the element thickness and whether it runs vertical or horizontal — an engineer comes back within one working day with the resin quantity, the port count, the quote and the datasheets. If injection is the wrong answer for your crack, we will say so.
