Grout injection is a useful repair and strengthening technique to intervene in old masonry buildings. Until now, a very limited amount of work has been reported on the potential of geopolymers for consolidation of old stone masonry walls. In the last decades there has been several research initiatives focus on the development of materials involving a higher volume of supplementary cementitious materials that substitute the traditional binders. Geopolymers that were developed as a part of these efforts, can not only reduce the dependence on traditional binders, but also potentially present materials with less environmental impacts and improved performance. This study investigates the fresh and hardened properties of grouts composed of natural hydraulic lime (NHL) and geopolymer. The experiments were conducted using a geopolymer made of fly ash, sodium hydroxide and water. The effects of the replacement of NHL by the fly ash-based geopolymer (at the dosages of 0, 20, 50, 80 and 100%) on the rheological parameters, stability, water absorption, compressive strength and durability were investigated. The results showed that the geopolymer-based grout has several advantages regarding the mechanical strength, durability and fresh stability, but the improvement of their rheological performances proved to be a challenging task. Overall, the findings of this study will be useful in assessing the design of grouts incorporating alternative binders and consequently contribute to the improvement of the grouting technique.