Abstract Appropriate surface saturation level is essential for the durability of the repaired structure. The repair material is often blamed for “not sticking”, although the general source of the trouble lies with the substrate surface conditioning. An extensive research project has been undertaken to develop specifications and performance criteria for surface preparation of concrete substrates. A field test was developed to evaluate the optimum moisture conditioning of the substrate concrete prior to application of repair material; this has been calibrated and compared with destructive and non-destructive on three types of concrete and two types of surface preparation. In order to evaluate different saturation levels, concrete samples have been stored in more than 12 modes of conservation. Finally, repair mortars have been applied on concrete substrates and adhesion was measured for different concrete surface saturation levels. Initial Surface Absorption Test (ISAT) can be used as an attractive quantitative test to evaluate saturation level of concrete substrate. Moreover, it is clearly shown that saturation levels higher than 50% and lower than 90% are requested for promoting adhesion of PCC mortars.