PU Grouting and PU injection Waterproofing Services PU Grouting Concrete Crack Injection Technique: Cracks in concrete happen overtime due to environmental issues such as thermal movement, drying shrinkage and other causes like nearby construction works or renovation works. If its not severe, it will be a minor problem and they will cause no instant issues or problems. But after some time, these minor and small cracks often become bigger problems and huge headaches, where water damage causes structural problems including reduced structural integrity due to water seepage.