For consolidation of weathered carbonate materials (such as marble, limestone and lime-based mortars) no fully satisfactory treatment currently exists. In this paper, an innovative phosphate treatment was investigated as a possible consolidant for limestone and compared with a commercial ethyl silicate (ES). The two treatments were evaluated in terms of effectiveness (i.e., ability to restore cohesion and mechanical properties, by measuring penetration depth, dynamic elastic modulus, tensile strength, resistance to abrasion) and compatibility (i.e., lack of any negative consequence on the original substrate, by assessing mechanical match, colour change, new phases composition, pore size distribution, water and water vapour transport properties, drying rate and thermal behaviour). The phosphate treatment proved to be very promising, being able to overcome some ES limitations.