Repair Materials & Methods
Curing cracks, concrete, dampness and corrosion.
With the diagnosis made, the cure must match the disease. A dormant crack is injected with epoxy; a moving one is routed and sealed or stitched. Spalled concrete is broken out, the steel cleaned and primed, and the section reinstated. Dampness is cured at its source, not painted over. Learn the methods, the repair materials and the rule that you always treat the cause, not the symptom.
Learning objectives
By the end of this lesson, you will be able to — mapped to the course outcomes for Building Maintenance & Repair:
Select a crack-repair method for a dormant or moving crack.
Sequence a concrete spall repair and treat the corroded steel.
Choose a dampness remedy that cures the source.
Apply corrosion protection and the main repair materials.
Crack & concrete repair
Rigid epoxy for dormant cracks, flexible methods for moving ones; for spalls, treat the steel first, then reinstate with polymer mortar or micro-concrete.[2]
Match the method to the crack
For a DORMANT structural crack, low-viscosity EPOXY INJECTION under pressure restores monolithic continuity. For a MOVING (active) crack, ROUTE AND SEAL (widen to a V-groove and fill with a flexible sealant) or STITCH it (metal dogs across the crack to restore tension). For SPALLED concrete the sequence is: break out the unsound concrete, clean and prime the exposed STEEL (treat the cause), then reinstate with a low-shrinkage POLYMER-MODIFIED MORTAR or MICRO-CONCRETE — or guniting/shotcrete and jacketing for larger areas.[2]
Dampness & corrosion
Dampness is cured at its source (DPC, tanking, drainage), and corroding steel is protected electrochemically — never just a coating over a live source.[1, 2]
Cure the source
Dampness is cured at its SOURCE, not painted over. For rising damp, insert a new DAMP-PROOF COURSE or CHEMICALLY INJECT a water-repellent to form one, and lower the external ground level. For below-grade walls, TANKING applies a continuous waterproof membrane. Surface and integral WATERPROOFING and corrected DRAINAGE manage the water. FLAG: the root cure is almost always managing the WATER (the gutter, the ground level, the flashing) — a surface coating over a live source only hides the problem until it returns worse.[1, 2]
At a glance
| Aspect | One | The other |
|---|---|---|
| Crack repair | Dormant: rigid epoxy injection | Moving: flexible route-and-seal / stitch |
| Spall repair | Treat the steel first (clean, prime) | Then reinstate (polymer mortar / micro-concrete) |
| Dampness | Myth: paint over the patch | Reality: cure the source (DPC, drainage) |
| Corrosion | Patch only: symptom returns | Cathodic protection: treats the cause |
| Material choice | Epoxy: structural, rigid | Sealant/fibre: movement & toughness |
Key terms
Pressure-injecting low-viscosity epoxy into a dormant structural crack to restore continuity.
Widening a moving crack to a V-groove and filling it with a flexible sealant.
Metal dogs/staples across a major crack to re-establish tensile continuity.
Cement mortar with a polymer for better adhesion and lower permeability — for patch repair.
A flowable, low-shrinkage material for reinstating larger spalled sections.
A barrier (inserted or chemically injected) stopping rising damp.
A continuous waterproof membrane applied to below-grade walls and basements.
Electrochemically polarising the steel so it cannot corrode — a permanent corrosion cure.
Studio task
For the spalled column you diagnosed earlier, write the repair specification step by step — the break-out, the steel treatment, the reinstatement material, and the corrosion protection — and name the repair material for each step.
Self-assessment
1. A fine, dormant structural crack in a concrete beam is best repaired by —
2. The root cure for rising damp is to —
3. Cathodic protection stops reinforcement corrosion by —
Recap
References & further reading
- [1]Barry A. Richardson, Defects and Deterioration in Buildings. Spon/Routledge, 2001.
- [2]Peter H. Emmons, Concrete Repair and Maintenance Illustrated. RSMeans/Wiley, 1993.
Further reading
- Peter Emmons, Concrete Repair and Maintenance Illustrated. Wiley.
- Concrete Society Technical Reports (repair). The Concrete Society.
- Barry Richardson, Defects and Deterioration in Buildings. Routledge.
Sources gathered and fact-checked June 2026. Published values vary by source, sample and method — treat as indicative and confirm against the cited standard before structural use.