On-site repair of deteriorated concrete and stone and other masonry is being done by a new technique developed in Britain. The process uses vacuum to impregnate concrete or friable stone with silane formulations, thus consolidating and weatherproofing it. Defective areas of concrete pavements or structures can be filled and repaired with polymers by this method. The work involves only a few steps: the area or object is covered with polyethylene film; air is then extracted from the pores or cavities of the concrete or stone by vacuum pumps, creating a low-pressure area; a suitable impregnant is then introduced beneath the polyethylene cover normal atmospheric pressure causes the impregnant to penetrate the previously evacuated pores or cavities. Two projects undertaken in Britain show how the process can be used for remedial work with failing grout. Rust stains on a post-tensioned concrete bridge indicated failure of grout in the tensioning ducts (confirmed by local engineers). The failure of the initial grouting had allowed water to reach the steel tendons and cause them to rust. The duct was successfully impregnated with a resin formulation. A different problem was faced by a major British company when the grout beneath crane rails in their automated warehouse began to crumble. Grout was failing under rails in all seven of the 390-foot-long aisles of the warehouse, and conventional patching repairs had not been successful. A test of the vacuum process was made on one aisle and the success of the test resulted in a contract to repair the other six. Of course, this process is not an answer for all civil engineering problems. It cannot be used where air leakage prevents the development of a low pressure area within a structure. Aside from this restriction, the process has been successful in a wide range of applications.