To help investigators determine the relative tightness of concrete details, surfaces, and surface treatments, a structural consulting company has developed a nondestructive instrument for use in quality control and forensic investigations. The portable, battery-operated instrument consists of a vacuum source and testing head. The instrument indicates tightness of concrete or concrete surface treatments in three ways: initial level of vacuum pressure reached, rate of vacuum pressure decline from the initial level, and, with the use of a foaming agent, the vigor of bubble formation. Some tests require interpretation and judgment by the investigator. When performing relative surface porosity tests, for example, and investigator can use a portion of the structure that is of known good quality as a reference. The tightness tester can quickly detect areas in the structure that may be more porous than the reference area.