Crack Injection Resin for Concrete: Products & Method

A crack that keeps coming back after you have filled it is almost always a crack that was never bonded through its depth. You fill the surface, paint over it, and within a season the line is back, sometimes wider than before.

This guide is about the permanent alternative: pressure-injected resin. It explains how injection differs from patching, how to tell a structural crack from a cosmetic one, when an engineer must be involved, which products suit which job, and how to inject concrete cracks in the right order. If your crack is leaking, there is a section on that too.

Crack Injection Resin for Concrete vs Surface Repair Mortar

Both methods repair concrete, but they solve different problems. Confusing them is the most common reason a "repaired" crack reopens.

How Pressure Injection Differs From a Surface Mortar

Pressure injection pushes a low-viscosity liquid resin, typically epoxy, into the crack through ports fixed along its length. The resin travels through the depth of the crack, fills it and bonds both faces back together, so the concrete can carry load across the line again.

A surface repair mortar does something else. It rebuilds the exposed face and edges of the concrete, and it does that well, but it sits on top of the crack rather than inside it.

A surface mortar alone does not bond a crack through its depth.

If you trowel mortar over a structural crack, the gap behind it stays open, water can still travel along it, and the repair will usually crack along the same line once the element moves again.

Where a Structural Repair Mortar Still Belongs

Mortar has its place, and the Mapei Lamposilex ZA structural repair mortar is a good example. It is listed for structural concrete repairs, with high mechanical strength and resistance to cracking and shrinkage, so it suits spalled corners, broken edges and damaged faces. A 5 kg unit costs around ZAR 441.72.

Where a crack has caused the surface to break away, the usual sequence is to inject the crack first and then reinstate the face with mortar. Injection does the bonding, and the mortar restores the profile.

Structural vs Non-Structural Cracks: Diagnose Before You Inject

Not every crack needs resin, and not every crack should be filled at all. Non-structural cracks are usually surface-level and stable, so they can often be filled and sealed without injection. Structural cracks tell a different story, and because the repair method depends entirely on which one you have, a careful look at the crack comes before any purchase.

Signs a Crack Is Structural, Not Cosmetic

Check the crack against these signs. Any one of them moves it out of the cosmetic category:

• It is widening or moving. If the crack grows over weeks or opens and closes with temperature, the cause is still active.
• The faces are offset. One side sits proud of the other, which means the concrete on either side is no longer moving together.
• Rust stains follow the line. Brown streaks mean water has reached the reinforcing steel and it is corroding.
• It sits in a load-carrying member. Cracks in beams, columns, lintels and suspended slabs carry more consequence than the same crack in a plaster skim.

A hairline crack that has not changed for a year, sits in a non-loaded wall and shows no staining is usually cosmetic. Mark its ends with a pencil and date them, then look again after a few weeks. That simple record tells you more than any guess.

When to Call a Structural Engineer

Call a structural engineer as soon as any structural sign shows. This applies above all to a crack that is still moving, one in a beam, column, lintel or load-carrying slab, and one showing signs of corrosion.

The reason is simple: resin cannot stop an active cause. If the crack is moving because of foundation settlement, overloading or failing reinforcement, injecting it only bonds the faces until the concrete cracks again beside the repair, so the engineer has to find the cause before you spend on materials.

What the Engineer Should Decide Before Any Resin Is Ordered

You want three answers on paper before you order anything:

1. Is the cause of the crack active, or has it stopped?
2. Is injection alone enough to restore the element, or does it need strengthening as well?
3. Which resin, injection pressure and cure conditions does the specification call for?

Some members need more than bonding. If the engineer decides a beam has lost capacity, injection may be paired with strengthening such as carbon fibre reinforcement for cracked concrete beams. Resin then restores continuity, and the reinforcement restores the strength.

This guide does not replace an engineer's assessment, and it is not a basis for deciding that a structural crack is safe to leave or safe to inject yourself.

Matching the Right Product to Each Concrete Crack

Pinnacle Construction Products is an authorised and certified distributor of brands including Mapei and ABE Construction Chemicals, and its team gives technical product advice. That means the choice below comes with manufacturer-approved backing rather than guesswork.

Epoxy Injection Resin for Structural Crack Repair

For a crack that needs bonding rather than facing, start with the ABE Epidermix 314 epoxy adhesive for structural concrete repair. It is listed for structural concrete repairs and surface reinstatement with reliable bonding performance. It comes in 2 l and 4 l sizes, at around ZAR 458.58 to ZAR 917.16.

Before you commit, read its technical data sheet for the injection details: mixing ratio, pot life, application conditions and cure. Those figures, not a general guide, set how you work. Our overview of epoxy adhesive options for concrete repair in South Africa goes deeper if you are comparing epoxies for different jobs.

If you are searching for Mapei crack injection systems specifically, send the crack details to the technical team and they will say which resin in the Mapei and ABE ranges fits your conditions. You can also see the full Mapei product range in South Africa for what that manufacturer covers.

Repair Mortars and Putty for Surface Work

Surface work divides into two jobs. Where concrete faces and edges need patching or restoring, the Lamposilex ZA mortar covered above is the option. Where the crack is cosmetic and non-structural, the goal is facing or filling, not injecting.

For those cosmetic cracks, Alcolin epoxy putty for cosmetic surface cracks is a mouldable putty listed for filling suitable cracks, holes and surface imperfections, with a smooth, paintable finish. A 2 x 60 g box costs around ZAR 62.72.

It is not a structural repair. Do not use it on a crack in a beam, column or slab that an engineer has flagged.

How to Inject Concrete Cracks, Step by Step

A proper injection follows a fixed order. Skipping a step, particularly sealing, is where most failed jobs go wrong, so work through the sequence below and follow the product's data sheet wherever it is more specific than this guide.

Prepare and Seal the Crack Before Injection

1. Clean and dry the crack as the datasheet requires. Dust, oil and standing water stop the resin from bonding to the faces.
2. Remove loose material. Chip away anything that is not sound concrete along the crack edges.
3. Seal both faces. Close the crack surface with a suitable sealing material so the resin cannot run out under pressure.
4. Fit injection ports along the line. Place them at the spacing the product data sheet or engineer's specification gives, and seal their bases firmly.

Because resin follows the path of least resistance, any gap in the seal becomes a leak the moment you apply pressure.

Pressure Injection, Curing and Final Checks

Mix the resin exactly to the datasheet, in the stated ratio and for the stated time. Mix only what you can inject within its pot life, since resin that starts to gel in the equipment is wasted and can block the ports.

On a vertical crack, start at the lowest port and work upward under controlled pressure. Keep going until resin shows at the next port, then cap the lower port and move to the next one. This pushes air ahead of the resin and out of the crack instead of trapping it.

Once every port has taken resin, leave it alone. Let it cure for the time the datasheet gives before you load the element or remove the ports. Then recheck the crack for any sign of reopening, and note the date of the repair.

Handle resin as the chemical it is. Wear gloves and eye protection, and work with good ventilation, especially in enclosed rooms and basements.

Polyurethane Injection for Water Leaks in Concrete

A crack that weeps or runs with water needs a different approach. Epoxies generally want a dry, clean crack, so a leaking crack calls for a resin chemistry suited to wet conditions, and polyurethane injection for water leaks in concrete is a common option because these resins can work where water is present. Check the datasheet of any resin you consider for its stated moisture tolerance, since this varies from product to product.

The surface is a separate matter. The Purtop 1000 N polyurethane waterproofing membrane is a Mapei membrane listed for demanding waterproofing applications, with high mechanical strength and durability. It protects the surface of a leaking area, but it does not fill the crack that carries the water.

If you coat a leaking crack without injecting it, water keeps finding its way through, and the membrane ends up fighting pressure from behind. Fill the crack first, then waterproof the surface.

For leaks in below-ground walls and floors, the wider options in our guide to waterproofing products for basements will help once the crack itself is dealt with.

Buying Crack Injection Resin in South Africa: Next Steps

Choosing crack injection resin for concrete in South Africa comes down to matching the product to the crack, not the other way round. The quickest route is to send Pinnacle's technical team the facts they need, so they can match a product to your job instead of offering a generic recommendation.

Include the following:

• Crack location: which element it is in, such as a slab, beam, column, lintel or wall, and whether it is internal or external.
• Photos: a close shot of the crack and a wider shot showing where it sits.
• Moisture condition: dry, damp, or actively leaking.
• Movement: whether it has widened, and any dated pencil marks or measurements you have.
• Engineer's specification: if an engineer has assessed it, send their instructions, since those govern the product choice.

The aim is a permanent fix, not another patch that you repeat next year. If you are a contractor buying for several jobs, ask the team about trade pricing when you send your details.

Send your crack details to the Pinnacle technical team today, and you will get a product match that fits the repair your concrete actually needs.

Frequently asked questions

Can I use repair mortar instead of injection resin on a structural crack?

No. A repair mortar rebuilds the exposed face and edges, but it does not fill or bond the crack through its depth. A structural crack needs resin injected under pressure so both faces are bonded, and mortar can then restore the surface afterwards.

How do I know if my concrete crack needs injection?

Look for widening or movement, offset faces, rust staining along the line, or a position in a beam, column, lintel or load-carrying slab. Any of these means it should be assessed by a structural engineer before you inject. A stable, surface-level hairline crack can usually just be filled and sealed.

Can I inject a crack that is leaking water?

Yes, but not with just any resin. A wet crack needs a chemistry suited to wet conditions, and polyurethane injection is a common choice. Check the datasheet for moisture tolerance, and use a waterproofing membrane only as a surface layer over the injected crack.

When can I load the element after injecting a crack?

Only once the resin has cured for the time given on its datasheet. Do not remove the ports or load the element earlier. After curing, recheck the crack for any sign of reopening.