Part three in our series on Effective Crack Prevention, Control and Repair discusses Repairing Cracks. Check out our first two posts on Crack Prevention and Crack Control.
Repairing Cracks
If your efforts at prevention and control are unsuccessful, you may be faced with a leaking crack that needs to be repaired. The most common repair method is to inject a product into the crack in an attempt to fill it and make the crack waterproof. Typically, a series of holes are drilled along the crack length so that they intersect the crack beneath the surface. A port is then inserted into each hole and a product is pumped into the crack. Common products include slurry mixtures of cement and/or clay with water, which can be cost effective for situations of minimal water flow and low-pressure. For more challenging repairs, hydrophilic urethane products are recommended. These react with water to produce a foam that quickly sets within the crack to block water flow. Urethane foam injection will normally remain flexible and tolerate a slight amount of movement in the concrete; however, this flexibility deteriorates with time.
An injection product that should never be used for waterproofing is epoxy. Epoxy injection is designed and used for restoring the strength and integrity of cracked concrete structural elements. These cracks must be relatively dry for the epoxy to achieve adhesion. Epoxy will not displace or react with water and therefore is largely ineffective at waterproofing a leaking crack.
All injection products suffer from the disadvantage of being somewhat hit and miss because both the drilling of the holes and injection of the material is done blind. Although the success rate can be high, achieving 100 per cent effectiveness is extremely difficult. Due to this, waterproofing and creating a completely dry structure is equally challenging and unreliable. Attempting to re-inject missed and still leaking areas can also be very difficult.
The only way to make certain a leaking crack is made completely waterproof is to open the crack and repair it directly. Cracks can be quickly chiseled open using an electric chipping hammer. The most common repair method involves chiseling the entire length of the crack to create a deep and narrow chase. The chase is then filled with hydraulic grout and preferably with a crystalline waterproofing system.
Crystalline waterproofing systems provide both a short-term physical barrier to water and long-term chemical waterproofing through the growth of pore-blocking crystals. Crystalline waterproofing is roughly equal to injection in the skill and time required, but is significantly cheaper and far more reliable. The limitation of this repair method is that it is not intended for cracks or joints experiencing movement. With quality products and proper training, even badly cracked and leaking concrete can be successfully repaired to a dusty-dry state. Because repairs are inconvenient and often expensive, your best crack repair strategy is to focus on prevention and control.