Restoring Structural Integrity in Cracked Concrete

Structural epoxy crack injection repairs dormant cracks in concrete slabs, beams, columns and walls by filling them with a low-viscosity epoxy resin that cures into a rigid, high-strength bond. When the crack is clean, dry and fully filled, the repair rebonds the two faces of the concrete so the member acts as one piece again. Cracks as narrow as 0.002 in. can be injected.

Nusite Group carries out epoxy injection as part of concrete and structural rehabilitation on parking structures, condominium, rental and office towers, and commercial, institutional and industrial buildings across the GTA and Southern Ontario. We work to the structural engineer’s assessment and repair specification.


Discuss Your Injection Waterproofing Project

A structural crack in an existing slab, beam, column or wall can usually be repaired in place, without demolition or taking the structure out of service for long.

Nusite Group can review the crack against the engineer’s assessment, confirm whether epoxy injection suits it, and plan the repair around the building’s operations.


When Epoxy Injection Is the Right Repair

Epoxy is the repair when strength is the problem and the crack has stopped moving. It suits:

  • Dormant structural cracks in slabs, beams, columns and walls
  • Cracks from overload, impact or a one-time settlement that has since stabilized
  • Cracks that must be rebonded to restore the member’s load path
  • Dry or near-dry cracks, from hairline width upward

It is the wrong repair in three situations:

  • Active leaks. Epoxy needs a dry crack to bond. Water in the crack weakens the bond and can wash resin out before it cures.
  • Moving cracks. Cured epoxy is often stronger than the surrounding concrete. If the crack is still opening and closing, a new crack forms beside the repair.
  • Corrosion cracks. Cracks caused by corroding reinforcement will return unless the corroded steel and delaminated concrete are repaired first through concrete restoration.

Epoxy and Water Leaks

Epoxy injection is a structural repair, not a leak repair. Where a structural crack is also leaking, the water is stopped first with polyurethane crack injection. Once the crack is dry, it is injected with epoxy to restore strength. Treating a wet structural crack with epoxy alone is one of the most common reasons crack repairs fail.


Engineering Review

A structural crack is a symptom. Before injection, the cause has to be understood: overload, restraint, settlement, corrosion or design. On most commercial and multi-residential projects that evaluation is made by the project’s structural engineer, who specifies the repair. We review the specification, confirm the crack is dormant and dry, and coordinate the work with the consultant and the property manager or general contractor.


The Epoxy Injection Process

  1. Assessment. The crack is mapped against the engineer’s specification and checked for movement and moisture.
  2. Cleaning. The crack surface is cleaned of dust, laitance and contaminants so the cap seal and resin bond properly.
  3. Ports and cap seal. Surface-mounted injection ports are set along the crack, and the crack face is sealed between them with an epoxy paste so resin cannot escape.
  4. Injection. Epoxy is injected at low, controlled pressure, starting at one end or the lowest port, and moved to the next port once resin appears there.
  5. Cure. The resin is left to cure fully in the crack.
  6. Finishing. Ports and cap seal are removed and the surface is ground flush.
  7. Verification. Where the engineer requires it, cores are taken across the crack to confirm the resin reached its full depth.

Selecting the Epoxy

Injection epoxies are selected by viscosity and by the conditions of the crack. Low-viscosity resins penetrate hairline cracks; thicker, gel-type resins hold in wider cracks and on vertical and overhead surfaces without running out. The engineer’s specification and the crack width set the material, and the cure time is planned around temperature, which matters on unheated parking levels through a Southern Ontario winter.


Where We Use Epoxy Injection

  • Parking structure slabs, beams and columns beneath condominium, rental and office towers, where cracking affects the structural members carrying traffic loads.
  • Podium and transfer slabs that support amenity decks, landscaping or the tower above.
  • Foundation and retaining walls with dormant structural cracks, once any active leak has been stopped.
  • Industrial and warehouse floor slabs cracked by heavy equipment and point loads.
  • Institutional buildings such as schools and hospitals, where repairs are phased around occupied space.

Epoxy vs. Polyurethane Crack Injection

Epoxy Polyurethane
Purpose Restores structural strength Stops water
Crack condition Dry, dormant Wet or actively leaking
Cured state Rigid, high-strength bond Flexible foam or gel
Movement Does not accommodate it Accommodates ongoing movement
Typical use Structural cracks in slabs, beams, columns and walls Shrinkage cracks, cold joints, penetrations

See Polyurethane Crack Injection, or the full comparison in Injection Waterproofing Materials: Polymer Gel vs. Polyurethane vs. Epoxy.


Cracks, Chlorides and Southern Ontario Parking Structures

In GTA parking structures, an open crack is a direct path for de-icing salt to reach the reinforcement. Sealing dormant structural cracks with epoxy closes that path and restores the member. Cracks that have already led to corrosion and delamination need concrete repair first, then crack injection, then a protective traffic coating where the slab is exposed to traffic and salt.


Why Project Teams Choose Nusite Group

  • Concrete and structural rehabilitation has been one of our core services since 1990
  • Fully bonded, licensed across Ontario, up to $10 million in liability coverage
  • Work carried out to the structural engineer’s specification, with coordination built into the schedule
  • Injection scopes self-performed by Nusite crews, not brokered to a third party
  • Material and labour warranties, with coverage varying by system and scope

Epoxy injection is one of four injection systems we install. See all methods on our Commercial Injection Waterproofing page.


FAQ

It is a structural repair in which a low-viscosity epoxy resin is injected under controlled pressure into a dormant crack in concrete. The resin fills the crack and cures into a rigid bond that rejoins the two faces, restoring the member’s integrity.

On actively leaking cracks, on cracks that are still moving, and on cracks caused by corroding reinforcement. Leaks are stopped first with polyurethane, moving cracks need a flexible repair, and corrosion cracks need concrete restoration before any injection.

Not on its own. Epoxy needs a dry crack to bond, so a leaking crack is sealed with polyurethane first. Once a dry, dormant crack is fully filled with epoxy, it no longer gives water a path through it.

Yes, when the crack is dormant, clean and fully filled. Cured epoxy bonds the concrete back together so the member carries load as one piece. The structural engineer determines whether injection alone is enough or whether additional strengthening is needed.

Cracks as narrow as 0.002 in. can be injected with low-viscosity epoxy. Wider cracks and vertical or overhead surfaces use thicker resins that stay in place while they cure.

In a dormant crack, cured epoxy is a long-term repair. A crack can reopen, usually beside the repair, if the cause is still active: continued movement, settlement or corrosion. That is why the cause is evaluated before injection. Our work carries material and labour warranties, with coverage varying by system and scope.

On most commercial and multi-residential structures, yes. A structural engineer evaluates the cause and specifies the repair, and we carry it out to that specification.

Epoxy restores strength and cures rigid, and is used on dry structural cracks. Polyurethane stops water and stays flexible, and is used on wet or moving cracks. Some cracks are treated with both.

We serve the Greater Toronto Area and Southern Ontario on commercial, institutional, industrial and multi-residential projects.


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