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Cracks Must be Repaired

A crack in concrete caused by movement in a structure can be a real problem. Walls and columns may be weakened by cracking. When strength is not a major issue, water enters through the crack can be even more troublesome than the crack itself. If a crack is not properly repaired, it will lead to extensive cracking and concrete spalling because steel reinforcement bars will be damaged by ingress of many corrosive minerals.

Epoxy Injection

Crack2.gif (62428 bytes)For sealing water leaks through cracks, epoxy injection gives the best results. Surface coatings will not usually seal cracks for long, neither the V-cut method. The side of the structure where water originates is called "positive" side and will normally inaccessible. However, waterproofing materials applied on "negative" side surface often fail because they depend on their bond strength to the surface.

The ideal injection is thin enough to penetrate small cracks and set quickly before any leaking water may push it out of the crack or away from the crack wall. To obtain a result of achieving structural strength, epoxy is a good material for the injection but it is only applied on dry or wet surface.

Injection Method

Injection is usually accompanied by machinery to obtain enough pressure to inject epoxy to the hairline cracks. Technique and patience are important for injection works. It is recommended that epoxy is injected along the crack at a certain interval of not less than the depth of the crack to ensure the crack is fully filled with. The injection process follows these simple steps:

  1. clean debris from the crack surface and try not to enlarge the crack surface. 

  2. flush the crack with water or compressed air if necessary to remove dust for easy  penetration. 

  3. injecting suitable epoxy.

Principle of Epoxy Injection

Epoxy injection is an effective method to seal up the crack completely and maintain the integrity of the structural, ensuring the best repairs to the crack in the concrete. It prevents the crack from further extending and stops water from leaking through the concrete. On the other hand, epoxy injection should be equipped with high pressure and low speed injection machine to achieve the best effects for filling up hairline concrete cracks. The theory is to inject epoxy at one point on the crack surface as beginning, the epoxy will gradually spread outward to another point for leaking (referring to below diagram that injection is carried out at point B and leaks at point C). With this procedure, epoxy injection is undertaken at one point by one point.


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Procedure :

Stick a plastic tape at an interval of 200mm (similar to the thickness of the concrete slab) along the crack as an inlet for injection or fix plastic tubes depending on the roughness of the concrete surface.

  1. Seal up the crack on concrete surface with epoxy E209 gel.

  2. After the E209 is dried up and hardened, the plastic tape can be torn out of the crack. (an inlet is left for injection on the crack as indicated at Point B in diagram.)

  3. With injection machine to inject epoxy E206 at the first point on the crack surface until the epoxy leaks at the second point. Using wax or soap to rub at the first point to stop the epoxy from running out temporarily.

  4. Repeat the above procedure to inject epoxy on the second point until epoxy leaks at third point and so on to the end of the crack.

  5. Finally, seal up the points of inlet for injection with the E209 on the crack.