Concrete Crack Repair: Choosing a Method

Before you repair cracks in concrete

Start by identifying the element: wall, facade, slab, beam, balcony or another part of the building. Then record the crack's position, direction and visible length. A close photograph is useful, but include a wider view showing corners, openings, joints and nearby staining.

Note whether the crack is new, reopening after repair or changing over time. Record rust marks, loose material, displaced edges and water entry. Do not chip away a high facade or remove loose concrete overhead to get a better photograph. Keep people clear of falling-material risks and arrange assessment.

Width alone is not enough to choose a repair. Location, depth, movement, moisture and the role of the element all matter. If structural movement or a load-bearing element is involved, the repair scope may require an engineer's assessment.

Match the method to the purpose

These categories help you compare proposals. They are not interchangeable products for every crack. The material specification needs to match the actual defect and the intended result.

Concrete crack injection: epoxy and polyurethane

Injection places a selected resin into a crack through a controlled repair process. Epoxy systems are commonly associated with bonding suitable cracks, while polyurethane systems include products intended for water sealing. The exact product properties and conditions determine suitability.

Ask why injection is proposed, what the chosen material is intended to achieve and whether the crack is expected to move. Also ask how moisture, contaminants, access and preparation will be handled. A product name on a quote does not describe those decisions by itself.

Where water is the concern, the entry path may need investigation alongside the visible crack. Our leak investigation service considers affected building interfaces and targeted remediation.

What happens during epoxy crack injection?

A cartridge injection system uses entry ports along the crack, with a surface seal to keep resin within the repair. The prepared bonding surface must be sound and free of oil, dust and loose material. Port positions, sealing of accessible faces and the resin choice follow the specified system.

1. Prepare the surface, attach the ports and seal the exposed crack line.
2. Let the surface seal harden before introducing the injection resin.
3. Inject in a controlled sequence, allowing trapped air to escape and checking movement of resin between ports.
4. After the resin sets, remove the temporary fittings and complete the agreed surface finish.

This differs from pushing filler into the visible surface. A rigid bonding system requires a crack suitable for that purpose; continuing movement needs a different design. The contractor should explain how they will confirm suitability and check the repair, including any inaccessible faces.

A step-by-step repair planning checklist

1. Record the defect. Label the location and date the photographs.
2. Establish the cause and objective. Separate appearance, leakage, movement and structural concerns.
3. Confirm the substrate. Assess the surrounding concrete and any loose or deteriorated material.
4. Select the system. Match preparation, repair materials and finish to the conditions.
5. Plan access and protection. Identify occupied areas, public routes and nearby surfaces.
6. Complete and check. Agree what the finished repair should achieve and how it will be assessed.
7. Keep the record. Retain materials, locations and any monitoring or maintenance instructions.

For a small, accessible surface repair, a DIY product may have a defined application in its instructions. Read the permitted use, preparation, moisture conditions and curing requirements before choosing it. Active leaks, moving cracks, overhead defects and structural concerns need a more considered assessment than filling the visible line.

When cracking comes with spalling or rust

Cracking accompanied by loose concrete or rust staining may need broader remediation. See our spalling concrete guide for signs to record. A thin surface filling will not replace missing concrete or address every cause of deterioration underneath.

Tell us whether fragments have fallen, whether reinforcement is visible and whether the affected area is over a doorway, footpath or occupied space. Photographs taken safely from below can help us discuss access, but keep out of an area where material could fall.

Our concrete repairs in Wellington cover the discussion of facade cracking, spalling, injection and repair finishes. Rope access can be considered for elevated work as part of the task-specific access assessment.

What a useful quote should include

Ask for the repair locations and extent to be identified, with preparation, materials and finishing work described separately. Include access, protection, disposal and whether adjoining coatings will be reinstated. Where further deterioration may be uncovered, agree how changes will be reported and priced.

Compare the intended outcome. A repair to reduce water passage is a different brief from a specified structural repair or a cosmetic surface finish. Make sure each proposal answers the same problem before comparing totals.

The cost depends on the repair extent, depth and condition, method, access and finish. Send previous reports and repair records with the enquiry. An existing coating or earlier filler can affect preparation and may help explain why an old repair has reopened.

After the repair

Keep dated photographs that show the same locations before and after the work. Follow the curing, use and care instructions for the installed system. If monitoring is part of the scope, record the agreed intervals and what changes should be reported.

Report new cracking, water entry or movement beside the repair. A useful completion record makes that follow-up much clearer than an invoice that only says 'crack repaired'.