Method Follows the Crack, Not the Other Way Round
There is no universal crack repair product. Each method addresses a specific combination of crack behaviour, material, and objective, and applying the wrong one produces a repair that fails without telling you why.
This guide describes the main methods and what each is for. Our crack repair page covers the service, and which method applies to a given crack comes from the assessment, covered in our guide on cosmetic versus structural crack repair.
Epoxy Injection
Objective: structural bonding. Restoring continuity across a crack in concrete so it is no longer a plane of weakness.
How it is done:
- The crack surface is cleaned and prepared.
- Injection ports are fixed along the crack at intervals.
- The surface between the ports is sealed so injected material cannot escape.
- Epoxy is injected under pressure at the lowest port, moving upward as it fills.
- Once cured, ports and surface seal are removed and the surface is dressed.
Why it works: cured epoxy is typically stronger than the concrete around it, so the repaired crack is no longer the weak line.
When it is right: dormant cracks in concrete where structural continuity matters.
When it is wrong: active cracks. Epoxy cures rigid, so continued movement produces a new crack alongside the repair. Also wrong in consistently wet conditions, because epoxy needs a dry, clean substrate to bond.
Polyurethane Injection and Sealing
Objective: water exclusion and tolerance of continued movement.
How it is done: injected or applied into the crack, where polyurethane reacts with moisture, expands, and cures to a flexible solid that fills the void and remains elastic.
Why it works: flexibility. The repair accommodates seasonal movement without debonding, and the expansion fills irregular voids the material finds.
When it is right: water-bearing cracks, cracks expected to continue moving seasonally, and any situation where excluding moisture rather than restoring capacity is the objective.
When it is wrong: where structural continuity is needed. A flexible material does not restore load capacity across a crack.
A useful property: polyurethane wants moisture to cure, which is why it works in conditions where epoxy would not.
Structural Carbon-Fiber Staples
Objective: reinforcing across a crack to resist further separation.
How it is done: the surface is ground back, a slot is cut across the crack perpendicular to its run, the surface is prepared, and the carbon-fiber staple is bedded in epoxy so it ties both sides together. Multiple staples are spaced along the crack.
Why it works: carbon fiber has very high tensile strength, and concrete’s weakness is tensile. The staple supplies what the concrete lacks across the crack.
When it is right: where a crack needs mechanical reinforcement rather than filling, and where adding thickness or excavating to install steel reinforcement is impractical.
When it is wrong: as a substitute for addressing an ongoing cause. Reinforcement resists movement; it does not remove whatever is driving it.
Mortar Joint Tuckpointing
Objective: restoring the weather seal and appearance of a masonry wall.
How it is done: deteriorated or cracked mortar is cut out to a sound depth, the joint is cleaned, and new mortar is packed in and finished to match the surrounding profile.
Why it works: it replaces failed mortar with sound mortar, which is what the joint needed.
When it is right: masonry joint failure where movement has stabilised.
When it is wrong: on a wall that is still moving. New mortar cracks along the same line, usually within a season or two.
Detail that matters: mortar mix compatibility. New mortar substantially harder than the surrounding masonry can damage the brick as it moves, particularly on older soft-fired brick.
Non-Shrink Grout
Used to fill voids and re-establish bearing where material has been lost, rather than as a crack filler. It appears in scopes where a bearing surface needs restoring.
Surface Filling
Flexible filler and paint for interior sheetrock cracking, where the objective is appearance on a stable crack. Legitimate and appropriate in that context. It is not a structural repair and a scope calling it one is wrong.
Moisture Conditions Matter
This is the detail that most often determines whether a repair holds.
Epoxy needs a dry, clean, sound substrate to bond. Polyurethane wants moisture, since that triggers its cure. Mortar needs the surrounding masonry appropriately dampened so it does not lose its water too quickly into dry brick.
Getting this wrong produces a repair that looks correct on completion day and debonds within a year. Surface preparation and moisture conditions belong in the method statement rather than being left to the day.
After the repair
Mark the repair and date it. Check after a season. A repair that holds confirms the crack was dormant and the method was right. A repair that reopens is not a workmanship failure, it is information: the movement is active and the question is a foundation question rather than a crack one.