Methods for measuring relative humidity (RH) in concrete floors - development and uncertainties

An RH method was proposed in the late 1970s to replace the traditional CM-method in Sweden and from 1984 the RH-method is the dominating method to measure moisture in concrete floors before applying a moisture sensitive floor covering. The required total uncertainty must be smaller than 2-3 % RH depending on the method used. The paper describes the historical development of RH measurements in concrete materials and structures as such and the development in Sweden for concrete floors during some 30 years. A number of decisive parameters are discussed and quantified such as sampling techniques, sample size, sample properties, moisture capacity of sensors and probes, calibration, drift of sensors and various temperature effects.