The efficiency of 16 products (with consolidating and/or water-repellency effects) applied to granites and limestones have been assessed by means of scanning electron microscopy (SEM). The technique offers the possibility of observing the porous system of the stone, the products' filming capacity, the penetration depth of the products into the stone, their distribution on the porous system, and their conservation degree through time. Scanning electron microscopy has to be considered as complementary to some other tests and techniques to assess the efficiency of conservation treatments, such as stone-water contact angle, water vapour permeability, and global colour variations, among others. The conclusion reached is that the SEM technique defines some of the parameters, properties, and characteristics that highly control the efficiency of the treatments. This work confirms the SEM technique, particularly using backscattering electrons, as a very useful and complementary tool to assess the efficiency of the conservation treatments applied to stone materials for restoration purposes.