In order to fill cracks, voids and discontinuities within masonry and marble architectural elements, documented after the fire of 1997 which damaged the Chapel of the Holy Shroud in Turin, the masonry at the lower part of the monument was grouted. The use of the hydraulic lime-based grout developed for the restoration of the Katholikon of Daphni Monastery, Greece, was selected. Laboratory tests of the selected grout have shown an evident flocculation, and the mixture was not injectable. In collaboration with the Hellenic Ministry of Culture, the materials and the applied procedures were meticulously examined, and it was proven that the main reason of failing to inject the grout was the use of low turbulence mixing, instead of the prescribed high turbulence one. Laboratory and in situ tests using a high turbulence mixer resulted to a grout of high injectability into voids of 0.2–0.4 mm. Its application to the masonry of the Chapel was successful, as proven by the results of sonic tomographies, before and after grouting application.