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Polyurethane (PU) injection or grouting is a type of waterproofing solution to solve problems not limited to only water leakage, but also concrete cracks, depressed concrete slab, and settlement problems due to its high expansion properties and short reacting period. PU resin is a type of fluid resin that can expand in the concrete structure, and thus produce the polyurethane foam and fill the cracks or voids on it. However, the physical properties of PU will change from liquid to solid after undergoing a specific chemical transformation process.

PU injection has short curing and repairing time, therefore, it is highly recommended to be adopted in sealing the visible active leaks observed in the concrete slabs. PU injection is a type of cost efficient waterproofing method to solve the leakage issue in residential properties, especially if the water is coming from the outside. For industrial properties, PU injection can be used to repair flooring which the area being damaged after repetitive use of heavy machinery.

Polyurethane (PU) resin possesses many characteristics that are effective for waterproofing. The flexible properties of polyurethane allow the movement of resins with the wall during contraction and expansion while keeping the voids sealed.  PU is a versatile polymer that can also be used in industrial applications such as surface coating and insulation purposes. Besides, its fast drying properties enable it to stop active leaks that may not be achieved using other waterproofing solutions. The PU injection also requires lesser maintenance and therefore cost of repairing works can be saved. For the cons part, PU injection is a corrective measure instead of a preventive measure like the other waterproofing solution. It repairs only places where leakages occur. Therefore, other locations with potential water leakage issues may not be prevented in advance. Subsequently, trained and skillful labor is required in the PU injection process in order to ensure the correct and effectiveness of the waterproofing.

Firstly, decide the location to conduct the PU injection and clean the area. Then, drill the holes at selected locations for PU injection at 45 degrees angle or less and the drilling depth should be around 2/3 of the structure thickness. Then, insert the packers into the holes. After that, inject the PU grout from the lowest packer by using a high-pressure injection grouting machine. High pressure will raise the polyurethane resin from the lower side of concrete to the upper side of the concrete. After the leakage has stopped, remove the packers and clean the exposed resins. Lastly, patch the drilling holes with cement-based waterproof materials.