Masonry presents some inadequacies due to its almost total lack of tensile strength. Typical damage to multiple leaf walls during earthquakes is the loss of bond between the leaves with consequent collapse of the external leaf. Retrofitting or repair of this damage is a very difficult task. In many cases grout injection or wall jacketing fail due to incompatibility with the construction technique of the walls. A complementary technique to the grouting has been proposed by the authors. Experimental results and applications of the technique on site have shown positive characteristics and the results of tests carried out on site show, in some cases, increases in shear strength and stiffness of the masonry walls.