Brazil has one of the largest hydroelectric parks in the world and important ventures for the world ranking have been executed in the country – to cite the most recent, Jirau and Belo Monte Hydraulic Power Plants (HPP). This emphasizes the importance in the continuous study of techniques and theories commonly used, in order to improve the quality of the projects. This work proposed to implement the Grouting Intensity Number (GIN) methodology for the grouting of waterproofing curtains, through back analysis and estimation of the results of the Jirau HPP foundation treatment. The GIN was chosen from an analysis of curves plotted on a scatter plot as points representing the ratio between the grouting volume (grouting for further analysis) and water (water loss test for estimation) vs. the injection pressure. The maximum grouting intensity selected for the Jirau spillway was 50 MPa × L/ m, which according to the method authors, Lombardi and Deere represents low fracture of the rock mass. Other authors also applied this methodology, finding values higher than in this paper. Therefore, continuity in studies of the application of GIN in projects in Brazil is important to validate its efficiency and to promote progress in this area of dam engineering.